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SYNTHESIS OF THE VULNERABILITY

An attacker can send a malformed UTF-8 character during a SIP
session, in order to block the SIP service of WebSphere
Application Server.

Severity: 2/4

Creation date: 01/08/2011

IMPACTED PRODUCTS

– IBM WebSphere Application Server

DESCRIPTION OF THE VULNERABILITY

The WebSphere Application Server product implements a SIP service.

The UTF-8 encoding can be used to represent Unicode characters on
several bytes:
– 1 to 7 bits : 0xxxxxxx
– 8 to 11 bits : 110xxxxx 10xxxxxx
– 12 to 16 bits : 1110xxxx 10xxxxxx 10xxxxxx
– 17 to 21 bits : 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

UTF-8 limits the encoding to 4 bytes and forbids usage of more
bytes than necessary. Bytes starting with bits 111110xx (or
superior bytes) thus cannot be used in a UTF-8 sequence.

However, when the SIP service of WebSphere AS receives a high
UTF-8 byte, it blocks instead of rejecting the sequence.

An attacker can therefore send a malformed UTF-8 character during
a SIP session, in order to block the SIP service of WebSphere
Application Server.

ACCESS TO THE COMPLETE VIGIL@NCE BULLETIN

http://vigilance.fr/vulnerability/WebSphere-AS-denial-of-service-via-SIP-UTF-8-10882