[NEWS] Apache ssl_callback_SSLVerify_CRL DoS

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Apache ssl_callback_SSLVerify_CRL DoS
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SUMMARY

"Apache is one of the the world's most widely used Web servers. Originally
developed in 1995 by a group that was to go on to become the The Apache
Group, the Apache HTTP Server is Open Source Software, and considered by
proponents to be fast, scalable and secure. The name was derived from the
project's less robust beginnings ('A patchy Web server')."

A buffer overrun vulnerability was recently reported in Apache, this
vulnerability could be exploited by malicious attackers to cause a denial
of service.

DETAILS

Vulnerable Systems:
* Apache HTTP Server version 2.0.54

Immune Systems:
* Apache HTTP Server version 2.0.55

A buffer overrun can be found in ssl_callback_SSLVerify_CRL( ) -
ssl_engine_kernel.c:
char buff[512]; /* should be plenty */
[...]
n = BIO_read(bio, buff, sizeof(buff));
buff[n] = '\0';

If there are more than 512 bytes the resulting value of n is 512, causing
us to write at location 512 (buff[512]) overflowing the buffer by one. The
line should read:
n = BIO_read(bio, buff, sizeof(buff) - 1);

ADDITIONAL INFORMATION

The original article can be found at:
<http://issues.apache.org/bugzilla/show_bug.cgi?id=35081>
http://issues.apache.org/bugzilla/show_bug.cgi?id=35081

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