Exim mail directory privilege escalation

exim-mail-directory-priv-escalation (59043) The risk level is classified as HighHigh Risk

Description:

Exim could allow a local attacker to gain elevated privileges on the system, caused by an error when handling hardlinks in the mail directory during the mail delivery process. If the mail directory is world-writable with a sticky-bit set, a local attacker could exploit this vulnerability to create hard links to arbitrary files of another user.

*CVSS:

Base Score: 4.6
  Access Vector: Local
  Access Complexity: Low
  Authentication: None
  Confidentiality Impact: Partial
  Integrity Impact: Partial
  Availability Impact: Partial
 
Temporal Score: 3.4
  Exploitability: Unproven
  Remediation Level: Official-Fix
  Report Confidence: Confirmed

Consequences:

Gain Privileges

Remedy:

Upgrade to the latest version of Exim (4.72 RC2 or later), available from the Exim Web site. See References.

References:

  • Exim Bugzilla Bug 988: CVE-2010-2023 - vulnerability with world-writable sticky mbox mail directory.
  • Exim Web site: exim Internet Mailer.
  • BID-40451: Exim Sticky Mail Directory Local Privilege Escalation Vulnerability
  • CVE-2010-2023: transports/appendfile.c in Exim before 4.72, when a world-writable sticky-bit mail directory is used, does not verify the st_nlink field of mailbox files, which allows local users to cause a denial of service or possibly gain privileges by creating a hard link to another user's file.
  • OSVDB ID: 65158: Exim transports/appendfile.c Hardlink Handling Arbitrary File Overwrite
  • SA40019: exim Hardlink Handling and MBX Locking Two Weaknesses

Platforms Affected:

  • Cambridge University Exim 4.66

Reported:

May 26, 2010

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