exploit the possibilities
Home Files News &[SERVICES_TAB]About Contact Add New

Broadcom Stack Buffer Overflow

Broadcom Stack Buffer Overflow
Posted Mar 23, 2017
Authored by Google Security Research, laginimaineb

Broadcom suffers from a buffer overflow vulnerability when parsing CCKM re-association responses.

tags | advisory, overflow
advisories | CVE-2017-6957
SHA-256 | c1de43d11bbe31e6686f56be6626ddf1603a025a1ae28eefb31e7a73be6cd66d

Broadcom Stack Buffer Overflow

Change Mirror Download
Broadcom: Stack buffer overflow when parsing CCKM reassociation response 

CVE-2017-6957


Broadcom produces Wi-Fi HardMAC SoCs which are used to handle the PHY and MAC layer processing. These chips are present in both mobile devices and Wi-Fi routers, and are capable of handling many Wi-Fi related events without delegating to the host OS.

In order to allow fast roaming between access points in a wireless network, the Broadcom firmware supports Cisco's "CCKM Fast and Secure Roaming" feature, allowing a client to roam to a new AP quickly. Note this is a different implementation to IEEE 802.11r-2008 FT.

When a client decides to roam to a different AP in a CCKM network, they first send a reassociation request to the AP containing a Cisco-specific information element. This AP responds by sending a reassociation response frame also containing a Cisco-specific IE (156). This IE is then parsed by the firmware in order to make sure it is valid, before completing the reassociation process. A packet capture containing this process can be found here: <a href="https://mrncciew.files.wordpress.com/2014/09/7921-cckm-roaming-to-lap1.zip" title="" class="" rel="nofollow">https://mrncciew.files.wordpress.com/2014/09/7921-cckm-roaming-to-lap1.zip</a>

On the BCM4339 SoC with firmware version 6.37.34.40 the reassociation response in handled by ROM function 0x78D04. This function first retrieves the Cisco-specific IE. Then, it proceeds to check that the IE is valid, by calling function 0x794F8. This function performs four validations:

1. Bytes [2:4] of the IE match Cisco's OUI (00-40-96)
2. Byte 5 of the IE is zero
3. (IE[20] | (IE[21] << 8)) + 30 == IE[1] + 2 (where IE[1] is the IE's length field)
4. Bytes [6:9] of the IE match bytes [14:17] of the IE in the reassociation request (see packet capture)

If the IE passes the checks described above, the function proceeds to call ROM function 0x79390. This function unpacks data from the IE, and has approximately the following high-level logic:

1. void function_79390(void* unk, char* ie, char* buf) {
2. char buffer[128];
3. memcpy(buffer, ..., 6); buffer += 6;
4. ...
5. memcpy(buffer, ie + 6, 4); buffer += 4;
6. *buffer = ie[10]; buffer += 1;
7. *buffer = ie[11]; buffer += 1;
8. memcpy(buffer, ie + 12, 8); buffer += 8;
9. memcpy(buffer, ie + 20, 2); buffer += 2;
10. memcpy(buffer, ie + 30, ie[20] | (ie[21] << 8));
11. ...
12. }

As can be seen above, line 10 performs a memcpy into the stack-allocated buffer ("buffer"), using the value "ie[20] | (ie[21] << 8)" as the length field. However, as we've previously seen, the only validation performed on these two bytes is that:

(ie[20] | (ie[21] << 8)) + 30 == ie[1] + 2

This means an attacker could craft a reassociation response frame containing a Cisco IE (156) as follows:

1. IE[2:4] = 0x00 0x40 0x96
2. IE[5] = 0
3. IE[20] | (IE[21] << 8) = 227
4. IE[1] = 255
5. IE[6:9] = REQIE[14:17]

This IE satisfies all the constraints validated by function 0x794F8. However, when the IE is the passed into function 0x79390, it will cause memcpy operation at line 10 in the code above to exceed the buffer's bounds, trigger a stack buffer overflow with attacker controlled data. It should be noted that there is no stack cookie mitigation in the BCM4339 firmware, meaning an attacker would not require an additional vulnerability primitive in order to gain code execution using this vulnerability.

I've verified this vulnerability statically on the BCM4339 chip with firmware version 6.37.34.40 (as present on the Nexus 5). However, I believe this vulnerability's scope includes a wider range of Broadcom SoCs and versions.

This bug is subject to a 90 day disclosure deadline. If 90 days elapse
without a broadly available patch, then the bug report will automatically
become visible to the public.



Found by: laginimaineb

Login or Register to add favorites

File Archive:

June 2022

  • Su
  • Mo
  • Tu
  • We
  • Th
  • Fr
  • Sa
  • 1
    Jun 1st
    19 Files
  • 2
    Jun 2nd
    16 Files
  • 3
    Jun 3rd
    28 Files
  • 4
    Jun 4th
    0 Files
  • 5
    Jun 5th
    0 Files
  • 6
    Jun 6th
    19 Files
  • 7
    Jun 7th
    23 Files
  • 8
    Jun 8th
    11 Files
  • 9
    Jun 9th
    10 Files
  • 10
    Jun 10th
    4 Files
  • 11
    Jun 11th
    0 Files
  • 12
    Jun 12th
    0 Files
  • 13
    Jun 13th
    0 Files
  • 14
    Jun 14th
    0 Files
  • 15
    Jun 15th
    0 Files
  • 16
    Jun 16th
    0 Files
  • 17
    Jun 17th
    0 Files
  • 18
    Jun 18th
    0 Files
  • 19
    Jun 19th
    27 Files
  • 20
    Jun 20th
    65 Files
  • 21
    Jun 21st
    10 Files
  • 22
    Jun 22nd
    8 Files
  • 23
    Jun 23rd
    6 Files
  • 24
    Jun 24th
    6 Files
  • 25
    Jun 25th
    0 Files
  • 26
    Jun 26th
    0 Files
  • 27
    Jun 27th
    0 Files
  • 28
    Jun 28th
    0 Files
  • 29
    Jun 29th
    0 Files
  • 30
    Jun 30th
    0 Files

Top Authors In Last 30 Days

File Tags

Systems

packet storm

© 2022 Packet Storm. All rights reserved.

Hosting By
Rokasec
close