A heap-based buffer overflow flaw was reported in the Exim's internal function string_vformat(). Additionally, it was identified that the overflow can be triggered via specially crafted SMTP protocol EHLO message, which may lead to unauthenticated remote code execution.
Upstream bug report:
The issue was fixed upstream in version 4.92.3.
Created exim tracking bugs for this issue:
Affects: epel-all [bug 1756934]
Affects: fedora-all [bug 1756933]
This is flaw was introduced in upstream version 4.92, where string_vformat() function was changed to use growable stings:
Earlier versions, including the version of Exim as shipped with Red Hat Enterprise Linux 5, did not contain the vulnerable code and were not affected by this issue.
The discussion on the oss-security mailing list indicates that the attacked using the EHLO command as described in the upstream bug report affects a process running with dropped privileges as exim user rather than root. Upstream did not rule out that there may be other vectors affecting other processes running with higher privileges as root.
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):