Release Date: 2004/11/22
   Author: [4]Stefan Esser [s.esser@ematters.de]
   Application: Cyrus IMAP Server <= 2.2.8
   Severity: Several vulnerabilities within Cyrus IMAP Server allow
   remote execution of arbitrary code
   Risk: Critical
   Reference: [5]http://security.e-matters.de/advisories/152004.html 
   Last Modified:   2004/11/22




   Overview
   IMAP (Internet Message Access Protocol) is an Internet standards-
   track protocol for accessing messages (mail, bboards, news, etc). The
   Cyrus IMAP server differs from other IMAP server implementations in
   that it is generally intended to be run on sealed servers, where
   normal users are not permitted to log in. The mailbox database is
   stored in parts of the filesystem that are private to the Cyrus IMAP
   system. All user access to mail is through the IMAP, POP3, or KPOP
   protocols.
   During an audit of imapd several vulnerabilities were discovered
   ranging from a standard stack overflow, over out of bounds heap
   corruptions, to a bug caused by the use of programming constructs that
   are undefined according to the C standard.
   All these bugs can lead to remote execution of arbitrary code
   depending on the skills of the attacker.



   Details
[01 - IMAPMAGICPLUS preauthentification overflow]

Affected Versions: 2.2.4 - 2.2.8

   When the option imapmagicplus is activated on a server the PROXY and
   LOGIN commands suffer a standard stack overflow, because the username
   is not checked against a maximum length when it is copied into a
   temporary stack buffer. This bug is especially dangerous because it
   can be triggered before any kind of authentification took place.
[02 - PARTIAL command out of bounds memory corruption]

Affected Versions: <= 2.2.6 (because unexploitable in 2.2.7, 2.2.8)

   Due to a bug within the argument parser of the partial command an
   argument like "body[p" will be wrongly detected as "body.peek".
   Because of this the bufferposition gets increased by 10 instead of 5
   and could therefore point outside the allocated memory buffer for the
   rest of the parsing process. In imapd versions prior to 2.2.7 the
   handling of "body" or "bodypeek" arguments was broken so that the
   terminating ']' got overwritten by a '\0'. Combined the two problems
   allow a potential attacker to overwrite a single byte of malloc()
   control structures, which leads to remote code execution if the
   attacker successfully controls the heap layout.
[03 - FETCH command out of bounds memory corruption]

Affected Versions: <= 2.2.8

   The argument parser of the fetch command suffers a bug very similiar
   to the partial command problem. Arguments like "body[p", "binary[p" or
   "binary[p" will be wrongly detected and the bufferposition can point
   outside of the allocated buffer for the rest of the parsing process.
   When the parser triggers the PARSE_PARTIAL macro after such a
   malformed argument was received this can lead to a similiar one byte
   memory corruption and allows remote code execution, when the heap
   layout was successfully controlled by the attacker.
[04 - APPEND command uses undefined programming construct ]

Affected Version: 2.2.7, 2.2.8

   To support MULTIAPPENDS the cmd_append handler uses the global stage
   array. This array is one of the things that gets destructed when the
   fatal() function is triggered. When the Cyrus IMAP code adds new
   entries to this array this is done with the help of the postfix
   increment operator in combination with memory allocation functions.
   The increment is performed on a global variable counting the number of
   allocated stages. Because the memory allocation function can fail and
   therefore internally call fatal() this construct is undefined
   arcording to ANSI C. This means that it is not clearly defined if the
   numstage counter is already increased when fatal() is called or not.
   While older gcc versions increase the counter after the memory
   allocation function has returned, on newer gcc versions (3.x) the
   counter gets actually increased before. In such a case the stage
   destructing process will try to free an uninitialised and maybe
   attacker supplied pointer. Which again could lead to remote code
   execution. (Because it is hard for an attacker to let the memory
   allocation functions fail in the right moment no PoC code for this
   problem was designed)



   Proof of Concept
   e-matters is not going to release exploits for any of these
   vulnerabilities to the public.



   Disclosure Timeline
   06. Nov 2004 Sent an email to the Cyrus IMAP team
   11. Nov 2004 Got reply from the Cyrus developers and shared the
   information with vendor-sec
   17. Nov 2004 Cyurs IMAP team contacted vendor-sec with the official
   patch
   22. Nov 2004 Cyrus IMAP Server 2.2.9 released
   22. Nov 2004 Public Disclosure




   CVE Information
   The Common Vulnerabilities and Exposures project (cve.mitre.org) has
   assigned the name CAN-2004-1011 to issue 01, the name CAN-2004-1012 to
   issue 02 and the name CAN-2004-1013 to issue 03.



   Recommendation
   It is strongly recommended to upgrade to the updated version of Cyrus
   IMAP Server as soon as possible because there is no workaround.



   GPG-Key
   [6][DOWNLOAD NEW GPG-KEY]
   pub 1024D/3004C4BC 2004-05-17 e-matters GmbH - Securityteam
   Key fingerprint = 3FFB 7C86 7BE8 6981 D1DA A71A 6F7D 572D 3004 C4BC



   Copyright 2004 [7]Stefan Esser. All rights reserved.