[ISN] Another big Apache hole found

[InfoSec News]

http://www.computerworld.com/securitytopics/security/story/0,10801,94191,00.html

By Matthew Broersma
JUNE 28, 2004
TECHWORLD.COM

LONDON - Linux and Unix vendors are releasing fixes for a critical bug
in the popular Web server Apache that could allow attackers to crash
the system or execute malicious code.

The bug affects Apache 1.3.x installations configured to act as proxy
servers, which relay requests between a Web browser and the Internet.  
When a vulnerable server connects to a malicious site, a specially
crafted packet can be used to exploit the vulnerability, according to
security researcher Georgi Guninski, who has publicly released exploit
code.

The bug is most serious on BSD installations, where it may allow code
execution, while on other platforms the most likely effect is a system
crash, researchers said. A reference in the Common Vulnerabilities and
Exposures database can be found here.

Guninski released information about the proxy-server bug earlier this
month, and last month discovered a similar vulnerability in an Apache
component offering Secure Sockets Layer encryption, but he said the
bugs don't reflect on Apache's overall security relative to
competitors such as Microsoft's Internet Information Services. "Still
Apache is much better than Windows," he said in an advisory.

Debian released a patch for the bug today, and Gentoo Linux released
its own patch last week. Red Hat Inc., OpenBSD and OpenPKG have also
released updates fixing the bug, while Novell Inc.'s Suse Linux said
in an advisory last week it is testing a patch. Researchers said
Apple's BSD-based Mac OS X is likely affected, but Apple has not yet
released a patch.

Apache versions 1.3.31, 1.3.29, 1.3.28, 1.3.27 and 1.3.26 are
affected, while the bug has been fixed in 1.3.32-dev, according to
security experts. System administrators can also get around the
problem by switching off Apache's proxy-server module.

"If I were running a BSD system, I would be very careful with this,"  
said Thomas Kristensen, CTO of Secunia, which maintains a database
tracking vulnerability advisories. "It's important to note that the
potential for code execution has not been proven to be exploitable,
but it pays to be safe." BSD is frequently used by Web hosting
companies, he said.

Kristensen said that despite the recent bugs, Apache's security is
solid overall. Both Apache and IIS have been so thoroughly studied
that few vulnerabilities are now discovered in their core components,
he said - with both servers, problems are now mostly found in
extensions such as mod_ssl and mod_proxy. "It's pretty solid as long
as you remember to configure it correctly and to disable the
extensions that are not necessary for your business," Kristensen said.

The bug in Apache's mod_proxy module means that a negative
user-specified length value may be used in a memory copy operation,
leading to corruption of memory and a buffer overflow. The exploit can
take effect when a remote server sends a negative Content-Length: HTTP
header field to the proxy server.

The proxy bug is the sixth vulnerability in Apache 1.3.x reported this
year, according to Secunia, which has recorded 10 such advisories in
2003 and 2004. Half of these were moderately or highly critical,
usually meaning they allowed remote access to the system or denial of
service. For comparison, IIS 5.x also had 10 advisories in the same
period, 40% of which were highly or extremely critical, Secunia said.

In 2002, the Slapper worm took advantage of a month-old bug in
Apache's mod_ssl component, causing widespread disruption.