Multiple Shell Metacharacter Injections in AFFLIB

Release Date	2007-04-27
Product	AFFLIB
Versions	2.2.0-2.2.8 and likely earlier versions
Severity	Low to Medium
Author	Timothy D. Morgan <tmorgan {at} vsecurity.com>
Vendor Status	Vendor Notified
CVE Candidate	CVE-2007-2055
Reference	Original Advisory

Product Description

From the forensicswiki.org website:

"The Advanced Forensics Format (AFF) is an extensible open format for the storage of disk images and related forensic metadata. It was developed by Simson Garfinkel and Basis Technology."

AFFLIB™ is the reference implementation of the AFF™ format, written primarily by Simson Garfinkel. It comes in the form of an open source library and a set of command line tools used to manipulate AFF™ files.

Vulnerability Overview

In mid-March, 2007 Virtual Security Research, LLC (VSR) performed a security code review of AFFLIB™ as a part of an internal tool assessment process. As a result, multiple vulnerabilities of varying severities were discovered. The most significant of these vulnerabilities are being announced publicly to raise awareness and help end-users secure themselves against potential attack.

VSR found that user-supplied command line parameters were used in several popen() calls without validation or escaping. The attack vectors available are limited, which reduces the overall severity of these problems.

These vulnerabilities remain exploitable in the latest release (2.2.8), even though an attempt was made to check for a set of shell metacharacters. All line numbers listed below are from version 2.2.0.

Vulnerability Details

The following sections include detailed descriptions of the specific instances of shell metacharacter injection found during the assessment.

Shell Command Injections in Decompression Calls

File: tools/afconvert.cpp
Lines: 245 & 255
Platforms Affected: Unix

A command line parameter is used without validation or escaping in a popen() call. If this command (or this function) receives parameters from an untrusted source, code execution would be a major risk. Lines 240-257 are included below for illustration:

    /* Check to see if it is a gzip file... */
    if(probe_gzip(infile)
       && yesno("infile looks like a gzip file","Uncompress it","Uncompressing")){
	/* Open with a subprocess. We will need to use zlib when we move to Windows. */
	char buf[256];
	sprintf(buf,"gzcat %s",infile);
	a_in = af_popen(buf,"r");
    }

    /* Check to see if it is a bzip2 file... */
    if(!a_in
       && probe_bzip2(infile)
       && yesno("infile looks like a bzip2 file","Uncompress it","Uncompressing")){
	/* Open with a subprocess. We will need to use bzip2zlib when we move to Windows. */
	char buf[256];
	sprintf(buf,"bzcat %s",infile);
	a_in = af_popen(buf,"r");
    }

	char buf[256];
	sprintf(buf,"gzcat %s",infile);
	a_in = af_popen(buf,"r");

Since af_popen() ultimately uses the popen() system call, and infile comes directly from a command line parameter, command line special characters could be injected if an attacker could control the input.

Shell Command Injection in Unused get_parameter Function

File: aimage/ident.cpp
Line: 190
Platforms Affected: Unix

A function parameter is used without validation or escaping in a popen() call. If this function (get_parameter) received arguments from an untrusted source, code execution would be a major risk. This function does not appear to be called at this time.

Vendor Response

Simson Garfinkel was first contacted on 2007-03-31. The following timeline outlines the responses from the vendor regarding this issue:

2007-04-01	Vendor was provided details of all vulnerabilities identified.
2007-04-03	Continued vendor communication.
2007-04-05	Vendor released version 2.2.6, containing multiple security fixes.
2007-04-06	Vendor notified VSR that fixes were released.
2007-04-09	VSR notified vendor that 9 vulnerability instances still remained in latest release.
2007-04-12	Vendor confirmed that remaining vulnerabilities would be fixed in next release.
2007-04-25	Vendor released versions 2.2.7 and 2.2.8. Vendor did not notify VSR.
2007-04-27	VSR discovered new versions were released. VSR inspected version 2.2.8 and found that no additional vulnerabilities were fixed. VSR advisories published.

Recommendation

AFFLIB™ users should upgrade to the newest version. Third-party projects which rely on AFFLIB™ should encourage users to upgrade, and/or incorporate fixes into their distribution of the library.

The update is available via:

http://www.afflib.org/downloads/

Common Vulnerabilities and Exposures (CVE) Information

The Common Vulnerabilities and Exposures (CVE) project has assigned the following name to these issues. This is a candidate for inclusion in the CVE list (http://cve.mitre.org), which standardizes names for security problems.

    CVE-2007-2055

References

1.	AFF - Forensics Wiki http://www.forensicswiki.org/wiki/AFF

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This advisory is distributed for educational purposes only, and comes with absolutely NO WARRANTY; not even the implied warranty of merchantability or fitness for a particular purpose. Virtual Security Research, LLC nor the author accepts any liability for any direct, indirect, or consequential loss or damage arising from use of, or reliance on, this information.

Vulnerability Disclosure Policy

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AFF™ and AFFLIB™ are trademarks of Simson Garfinkel and Basis Technology Corp. Included source code excerpts are copyright Simson Garfinkel and Basis Technology Corp. This advisory is copyright © 2007 Virtual Security Research, LLC. All rights reserved.