LibSMI smiGetNode Buffer Overflow When Long OID Is Given In Numerical Form

LibSMI smiGetNode Buffer Overflow When Long OID Is Given In Numerical Form

Advisory ID Internal

1. Advisory Information

Title: LibSMI smiGetNode Buffer Overflow When Long OID Is Given In Numerical Form
Advisory Id: CORE-2010-0819
Date published: 2010-10-20
Date of last update: 2010-10-20
Vendors contacted: Libsmi team
Release mode: Coordinated release

2. Vulnerability Information

Class: Failure to Constrain Operations within the Bounds of a Memory Buffer [CWE-119]
Impact: Code execution
Remotely Exploitable: Yes
Locally Exploitable: Yes
CVE Name: CVE-2010-2891
Bugtraq ID: N/A

3. Vulnerability Description

A statically allocated buffer is overwritter in the case that a very long Object Identifier is specified in stringified dotted notation to the smiGetNode function of libsmi[1]. This may result in arbitraty code execution by cleverly overwriting key pointers in memory.

4. Vulnerable packages

  • libsmi 0.4.8.
  • Any software that uses the vulnerable function to find a definition from an Object Indentifier specified in stringified dotted notation that is given by the user. The SNMP packets from the protocol that travel over the network do not use this notation for OIDs.

5. Non-vulnerable packages

  • libsmi 0.4.8 patched with the supplied patch.
  • Any future release of libsmi, or current SVN head revision, since this patch was already commited to their repositories.

6. Vendor Information, Solutions and Workarounds

This patch was supplied by Juergen Schoenwaelder and fixes the bug:

Index: lib/smi.c =================================================================== --- lib/smi.c (revision 29144) +++ lib/smi.c (working copy) @@ -1793,10 +1793,15 @@ } if (isdigit((int)node2[0])) { - for (oidlen = 0, p = strtok(node2, ". "); p; + for (oidlen = 0, p = strtok(node2, ". "); + p && oidlen < sizeof(oid)/sizeof(oid[0]); oidlen++, p = strtok(NULL, ". ")) { oid[oidlen] = strtoul(p, NULL, 0); } + if (p) { + /* the numeric OID is too long */ + return NULL; + } nodePtr = getNode(oidlen, oid); if (nodePtr) { if (modulePtr) {


7. Credits

This vulnerability was discovered and researched by Andres Lopez Luksenberg from Core Security Technologies. The publication of this advisory was coordinated by Pedro Varangot.

8. Technical Description / Proof of Concept Code

The smiGetNode function returns a SmiNode struct given the name of a OID as a char * in both either numeric (i.e. "") or human readable format (i.e. "ipForwarding"). This function uses a static array of 128 elements of type unsigned int to hold the OID in numeric format:

 SmiSubid oid[128];


Note that SmiSubid is a typedef of unsigned int.

This array is populated by a loop that calls strtok and then subsecuently strtoul in the case that the OID supplied as a char * was in the form of subsecuent numbers separated by a period.

 if (isdigit((int)node2[0])) { for (oidlen = 0, p = strtok(node2, ". "); p; oidlen++, p = strtok(NULL, ". ")) { oid[oidlen] = strtoul(p, NULL, 0); } }


That loop clearly overwrites past oid boundaries when the string contained in node2 has more that 128 dots ("."). This constitutes a classical overflow that can likely be leveraged into arbitrary code execution reliably.

To verify if the version on libsmi installed on a unix based system is vulnerable, the code example (smisubtree) from man libsmi[2] can be used. This programs calls smiGetNode in the following way in line 17:

 for((smiNode = smiGetNode(NULL, argv[1])) &&}


The program crashes when called via commandline with an OID with more than 128 numeric tokens, like the OID outputed by the following Python script:

 #!/usr/bin/python # run ./smisubtree `./` if __name__ == "__main__": s = "" for i in xrange(158): s = s + "1." print s}


9. Report Timeline

  • 2010-09-06: Core Security contacts Vincent Bernat, the Debian Package Maintainer for libsmi, informing that a bug has been found in libsmi. Core Security Technologies asks for a security contact in upstream stating that finding a reliable one using Google or looking at mailing lists was difficult.
  • 2010-09-06: Vincent Bernat, the Debian Package Maintainer for libsmi, replies with two e-mail of aledged developers of libsmi, Juergen Schoenwaelder and Frank Strauss.
  • 2010-09-07: Core Security Technologies contacts Juergen Schoenwaelder and Frank Strauss at their supplies e-mail addresses, telling about a found vulnerability and offering an advisory draft in either plain or encripted form.
  • 2010-09-07: Frank Strauss' e-mail address bounces Core Security's e-mail back, informing about a new e-mail address. Core Security sends the message again to the new address.
  • 2010-09-07: Juergen Schoenwaelder replies with his PGP keys, and copies Vincent Bernat again in the conversation.
  • 2010-09-09: Core Security sends and encripted draft of this advisory to Juergen Schoenwaelder and Vincent Bernat, with apologies due to the delay caused by Pedro Varangot being on leave due to health issues. The advisory draft mentions Net-SNMP as possible vulnerabile software.
  • 2010-09-11: Juergen Schoenwaelder replies with a patch fixing the vulnerability, and correcting some tecnical information in the advisory draft regarding the impact of the vulnerability, stating that it is likely low and that Net-SNMP is not affected.
  • 2010-09-27: Core Security replies to Juergen Schoenwaelder and Vincent Bernat agreeing that the impact of the vulnerability is low and removes the mention of Net-SNMP in the avisory. Core Security Technologies asks for a timeline regarding the release of a fixed version of libsmi stating that this advisory will be released anyway, because someone may be using libsmi in his software introducing a vulnerability he may not know about. No reply is received for this e-mail.
  • 2010-10-04: Core Security notifies Juergen Schoenwaelder and Vincent Bernat that October the 18th has been set as a tentative release date for this advisory, and that the release date is open to discussion if commitment to release a fixed version of libsmi in a given timeframe is given.
  • 2010-10-08: Juergen Schoenwaelder replies with sugestions for the vulnerable packages and vendor information section of this advisory. He also mentions that Core Security Technologies should go with the October de 18th release date for this advisory.
  • 2010-10-08: Core Security incorporates Juergen Schoenwaelder's suggestions to the advisory, and again mentions that the advisory can be rescheduled if it is deemed necesary by the vendor.
  • 2010-10-20: Advisory CORE-2010-0819 is released.


10. References


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12. About Core Security 

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13. Disclaimer

The contents of this advisory are copyright (c) 2010 Core Security and (c) 2010 CoreLabs, and are licensed under a Creative Commons Attribution Non-Commercial Share-Alike 3.0 (United States) License: