Slapper worm spanks Apache servers
A virulent Linux worm is creating an attack network on the
Internet, security clearing house CERT
warned this weekend.
Slapper exploits a previously-disclosed
OpenSSL vulnerability, to create an attack platform for
distributed denial-of-service (DDoS) attacks against other
sites. The worm also has backdoor functionality,
according to, security tools vendor ISS. It describes the
malicious code as a variation of the much less virulent Apache
"Scalper" BSD worm.
The OpenSSL server vulnerability exploit exists on a wide
variety of platforms, but Slapper appears to work only on
Linux systems running Apache with the OpenSSL module (mod_ssl)
on Intel architectures.
The Slapper worm was first seen on Friday the 13th. Since then
it has infected thousands of web servers around the world and
continues to spread. By late last night
servers were infected with the worm, according to AV
The worm scans for potentially vulnerable systems on 80/tcp
using an invalid HTTP GET request (GET /mod_ssl:error:HTTP-request
When an Apache system is detected, it attempts to send exploit
code to the SSL service via 443/tcp. If successful, a copy of
the malicious source code is then placed on the victim server,
where the attacking system tries to compile and run it. Once
infected, the victim server begins scanning for additional
hosts to continue the worm's propagation.
During the infection process, the attacking host instructs the
newly infected victim to initiate traffic on 2002/UDP back to
the attacker. Once this communications channel has been
established, the infected system becomes part of the worm's
For this reason blocking port 2002/UDP at enterprise firewalls
may be a good idea.
While the Windows-affecting Nimda nor Code Red worms attacked
nearby subnets indiscriminately, Slapper creates a
peer-to-peer network that an attacker can harness for attacks.
This troubling development sets Slapper apart from other
Binary and source code versions of the worm are available and
are being actively circulated - and access to the source code
might lead to the development of more powerful variants.
The vulnerability exploited by the Slapper (Apache/mod_ssl)
worm was fixed beginning with OpenSSL version 0.9.6e.
Administrators may want to upgrade to the latest version as of
this writing the latest version of OpenSSL is 0.9.6g.
Users should also update their AV software to detect the worm.
Internet Security Systems Security Alert
September 14, 2002
"Slapper" OpenSSL/Apache Worm
ISS X-Force has learned of the active
propagation of a worm which exploits a previously disclosed
vulnerability in Secure Sockets Layer 2.0 (SSLv2) handshake
process. The worm is a modified derivative of the Apache
"Scalper" BSD worm. Current versions of the Slapper worm that
are in the wild are targeting Linux servers running Apache
with mod_ssl. The worm has distributed denial of service
(DDoS) capabilities, as well as backdoor functionality.
Netcraft.com reports that over 66% of all active Web servers
on the Internet are running Apache. Securityspace.org reports
that there are nearly 1.4 million OpenSSL installations on the
Apache/mod_ssl servers with affected
OpenSSL versions are being actively compromised. Once a server
is infected, the backdoor can be accessed without any
authentication. This may lead to third-parties using infected
hosts to launch future DDoS attacks. X-Force has received
reports that the DDoS capabilities associated with this worm
are very powerful and have already been used to attack and
disable high-profile targets. Binary and source code versions
of the worm are available and are being actively circulated.
Widespread access to the source code of this worm may lead to
the development of more powerful variants.
OpenSSL versions up to and including
0.9.6d and 0.9.7 beta1
Current versions of the Slapper worm
only target the following Linux distributions. The worm may
trigger unpredictable results on additional Unix platforms.
Other Unix platforms, as well as Apache with OpenSSL for
Windows may also be vulnerable to the OpenSSL vulnerability.
Debian Linux, Apache 1.3.26
RedHat Linux, Apache 1.3.6
RedHat Linux, Apache 1.3.9
RedHat Linux, Apache 1.3.12
RedHat Linux, Apache 1.3.19
RedHat Linux, Apache 1.3.20
RedHat Linux, Apache 1.3.23
SuSE Linux, Apache 1.3.12
SuSE Linux, Apache 1.3.17
SuSE Linux, Apache 1.3.19
SuSE Linux, Apache 1.3.20
SuSE Linux, Apache 1.3.23
Mandrake Linux, Apache 1.3.14
Mandrake Linux, Apache 1.3.19
Mandrake Linux, Apache 1.3.20
Mandrake Linux, Apache 1.3.23
Slackware Linux, Apache 1.3.26
Gentoo Linux (Apache version
For the complete ISS X-Force Security
Advisory, please visit: