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: https://bugs.exim.org/show_bug.cgi?id=2449 Upstream commit: https://git.exim.org/exim.git/commitdiff/478effbfd9c3cc5a627fc671d4bf94d13670d65f The issue was fixed upstream in version 4.92.3.
External References: https://exim.org/static/doc/security/CVE-2019-16928.txt
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: https://git.exim.org/exim.git/commitdiff/d12746bc15d83ab821be36975da0179672708bc1 https://git.exim.org/exim.git/commitdiff/1100a343aead3a686a31652d78e4b64dc5e982e5 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. https://seclists.org/oss-sec/2019/q3/255
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s): https://access.redhat.com/security/cve/cve-2019-16928
Statement: This issue did not affect Red Hat Enterprise Linux 5 as the exim package did not contain the vulnerable code in any of our supported products.