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Zero Day DOS Vulnerability In Apache Leaves Half Of Internet Vulnerable

Few days ago a massive DOS vulnerability was found in Apache's version 1.3 and 2.x, leaving more than 50% of the internet vulnerable to DOS attack, This Dos attack is so powerful that a single computer can take down the whole server. A new tool named Apachekiller has been observed actively in wild.

According to Apache:

Apache HTTPD Security ADVISORY
Title: Range header DoS vulnerability Apache HTTPD 1.3/2.x
CVE: CVE-2011-3192:
Date: 20110824 1600Z
Product: Apache HTTPD Web Server
Versions: Apache 1.3 all versions, Apache 2 all versions
A denial of service vulnerability has been found in the way the multiple
overlapping ranges are handled by the Apache HTTPD server:

An attack tool is circulating in the wild. Active use of this tools has
been observed.
The attack can be done remotely and with a modest number of requests can
cause very significant memory and CPU usage on the server.

The default Apache HTTPD installation is vulnerable.
There is currently no patch/new version of Apache HTTPD which fixes this
vulnerability. This advisory will be updated when a long term fix
is available.

A full fix is expected in the next 48 hours.

Apache Killer

Apache killer is a DDOS/DOS tool written in Perl which sends HTTP GET REQUESTS with multiple byte ranges, These byte ranges occupy a wide variety of portions in the memory space which when abused causes Apache to malfunction.

Currently there is no patch released by Apache regarding this issue, However apache have suggested some immediate mitigation tips. Which are stated as follows:

However there are several immediate options to mitigate this issue until
a full fix is available:
1) Use SetEnvIf or mod_rewrite to detect a large number of ranges and then
either ignore the Range: header or reject the request.
Option 1: (Apache 2.0 and 2.2)
# Drop the Range header when more than 5 ranges.
# CVE-2011-3192
SetEnvIf Range (,.*?){5,} bad-range=1
RequestHeader unset Range env=bad-range
# optional logging.
CustomLog logs/range-CVE-2011-3192.log common env=bad-range
Option 2: (Also for Apache 1.3)
# Reject request when more than 5 ranges in the Range: header.
# CVE-2011-3192
RewriteEngine on
RewriteCond %{HTTP:range} !(^bytes=[^,]+(,[^,]+){0,4}$|^$)
RewriteRule .* - [F]
The number 5 is arbitrary. Several 10's should not be an issue and may be
required for sites which for example serve PDFs to very high end eReaders
or use things such complex http based video streaming.
2) Limit the size of the request field to a few hundred bytes. Note that while
this keeps the offending Range header short - it may break other headers;
such as sizeable cookies or security fields.

LimitRequestFieldSize 200
Note that as the attack evolves in the field you are likely to have
to further limit this and/or impose other LimitRequestFields limits.
See: http://httpd.apache.org/docs/2.2/mod/core.html#limitrequestfieldsize
3) Use mod_headers to completely dis-allow the use of Range headers:
RequestHeader unset Range

Note that this may break certain clients - such as those used for
e-Readers and progressive/http-streaming video.
4) Deploy a Range header count module as a temporary stopgap measure:
Precompiled binaries for some platforms are available at:
5) Apply any of the current patches under discussion - such as:

Apache Killer In Action

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