|Category:||Ubuntu Local Security Checks|
|Title:||Ubuntu USN-170-1 (gnupg)|
|Summary:||Ubuntu USN-170-1 (gnupg)|
The remote host is missing an update to gnupg
announced via advisory USN-170-1.
A security issue affects the following Ubuntu releases:
Ubuntu 4.10 (Warty Warthog)
Ubuntu 5.04 (Hoary Hedgehog)
The following packages are affected: gnupg
Serge Mister and Robert Zuccherato discovered a weakness of the
symmetrical encryption algorithm of gnupg. When decrypting a message,
gnupg uses a feature called quick scan
this can quickly check
whether the key that is used for decryption is (probably) the right
one, so that wrong keys can be determined quickly without decrypting
the whole message.
A failure of the quick scan will be determined much faster than a
successful one. Mister/Zuccherato demonstrated that this timing
difference can be exploited to an attack which allows an attacker to
decrypt parts of an encrypted message if an oracle is available, i.
e. an automatic system that receives random encrypted messages from
the attacker and answers whether it passes the quick scan check.
However, since the attack requires a huge amount of oracle answers
(about 32.000 for every 16 bytes of ciphertext), this attack is mostly
theoretical. It does not have any impact on human operation of gnupg
and is not believed to be exploitable in practice.
The updated packages disable the quick check, which renders this
timing attack impossible.
The problem can be corrected by upgrading the affected package to
version 1.2.4-4ubuntu2.1 (for Ubuntu 4.10), or 1.2.5-3ubuntu5.1 (for
Ubuntu 5.04). In general, a standard system upgrade is sufficient to
effect the necessary changes.
Risk factor : Medium
BugTraq ID: 12529|
Common Vulnerability Exposure (CVE) ID: CVE-2005-0366
SuSE Security Announcement: SUSE-SR:2005:007 (Google Search)
CERT/CC vulnerability note: VU#303094
|Copyright||Copyright (c) 2005 E-Soft Inc. http://www.securityspace.com|
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