SA04-002 - Apache config file env variable buffer overflow
* SITIC Vulnerability Advisory *
Advisory Name: Apache config file env variable buffer overflow
Advisory Reference: SA04-002
Date of initial release: 2004-09-15
Product: Apache 2.0.x
Platform: Linux, BSD systems, Unix, Windows
Effect: Code execution when processing .htaccess files
Vulnerability Identifier: CAN-2004-0747
Overview:
Apache suffers from a buffer overflow when expanding environment variables
in configuration files such as .htaccess and httpd.conf. In a setup typical
of ISPs, for instance, users are allowed to configure their own public_html
directories with .htaccess files, leading to possible privilege escalation.
Details:
The buffer overflow occurs when expanding ${ENVVAR} constructs in .htaccess
or httpd.conf files. The function ap_resolve_env() in server/util.c copies
data from environment variables to the character array tmp with strcat(3),
leading to a buffer overflow.
HTTP requests that exploit this problem are not shown in the access log. The
error log will show Segmentation faults, though.
Mitigating factors:
Exploitation requires manual installation of malicious .htaccess files by
someone with normal user rights.
Affected versions:
o Apache 2.0.50
o many other 2.0.x versions
Recommendations:
o A fix for this issue is incorporated into Apache 2.0.51
o For Apache 2.0.*: The Apache Software Foundation has published a patch
which is the official fix for this issue.
Patch information:
o The Apache 2.0.51 release is available from the following source:
http://httpd.apache.org/
o For Apache 2.0.*, the patch is available from the following source:
http://www.apache.org/dist/httpd/patches/apply_to_2.0.50/
Acknowledgments:
This vulnerability was discovered by Ulf Harnhammar for SITIC, Swedish IT
Incident Centre.
Contact information:
Swedish IT Incident Centre, SITIC
P O Box 5398, SE-102 49 Stockholm, Sweden
Telephone: +46-8-678 5799
Email: sitic at pts dot se
http://www.sitic.se
Revision history:
Initial release 2004-09-15
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