Two weaknesses and a vulnerability have been reported in Exim, which can be exploited by malicious, local users to perform certain actions with escalated privileges and by malicious people to compromise a vulnerable system.
1) An error when handling hardlinks within the mail directory during the mail delivery process can be exploited to e.g. append information to arbitrary files of another user.
Successful exploitation of this weakness requires that the mail directory is world-writable with the sticky bit set.
2) A race condition related to the MBX locking can be exploited to e.g. change the permissions of another user's file via symlink attacks.
Successful exploitation of this weakness requires that MBX locking is used.
3) An error in the "string_vformat()" function in src/string.c can be exploited to cause a buffer overflow e.g. when headers of a specially crafted, rejected email are being logged.
Successful exploitation of this vulnerability allows execution of arbitrary code.
This vulnerability is reported in versions prior to 4.70.
Provided and/or discovered by: 1, 2) Dan Rosenberg
3) Reported as an 0-day.
Original Advisory: http://lists.exim.org/lurker/message/20100524.175925.9a69f755.en.html
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Subject: Exim Weaknesses and Buffer Overflow Vulnerability
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