libspf2: DNS response buffer overflow

Background

libspf2 is a library that implements the Sender Policy Framework, allowing mail transfer agents to make sure that an email is authorized by the domain name that it is coming from. Currently, only the exim MTA uses libspf2 in Gentoo.

Description

libspf2 uses a fixed-length buffer to receive DNS responses and does not properly check the length of TXT records, leading to buffer overflows.

Impact

A remote attacker could store a specially crafted DNS entry and entice a user or automated system using libspf2 to lookup that SPF entry (e.g. by sending an email to the MTA), possibly allowing for the execution of arbitrary code.

Workaround

There is no known workaround at this time.

Resolution

All libspf2 users should upgrade to the latest version:

 # emerge --sync
 # emerge --ask --oneshot --verbose ">=mail-filter/libspf2-1.2.8"