oCERT Advisories

#2009-013 yTNEF/Evolution TNEF attachment decoder input sanitization errors

Description:

yTNEF, an open source filter program that decodes Transport Neutral Encapsulation Format (TNEF) e-mail attachments, and the Evolution TNEF attachment decoder plugin suffer from directory traversal and buffer overflow vulnerabilities.

The vulnerabilities lead to arbitrary code execution with the privilege of the target user running the decoders.

The directory traversal vulnerability is caused by improper sanitization of the file name used for saving the attachments, as it is computed directly from properties contained in the TNEF structure without checking for conditions that allow to traverse outside the temporary directory used for attachment storage. This leads to arbitrary code execution in case the attacker crafts an attachment that would overwrite a file used for execution (as an example the bashrc profile).

Additionally buffer and heap overflow vulnerabilities can be triggered by passing a file name exceeding a fixed size of 256 bytes in the TNEF data structure. This can lead to arbitrary code execution if exploited.

Affected version:

yTNEF, all versions

Evolution TNEF plugin, all versions

Fixed version:

yTNEF, N/A

Evolution TNEF plugin, N/A

Credit: vulnerability report and PoC code received from Yorick Koster < yorick [at] akitasecurity [dot] nl >.

CVE: CVE-2009-3721 (buffer overflow), CVE-2009-3887 (directory traversal)

Timeline:

2009-07-09: vulnerability report received
2009-07-10: contacted ytnef and evolution maintainers
2009-07-11: former evolution plugin maintainer communicates that code is unmaintained, voluntarily deletes online copy
2009-07-21: contacted affected vendors, advising to remove or disable the unmaintained code
2009-09-05: advisory release
2009-10-28: assigned CVE
2009-11-06: assigned separate CVE for traversal issue

References:
http://www.akitasecurity.nl/advisory.php?id=AK20090601

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