Bug 1756930 (CVE-2019-16928) - CVE-2019-16928 exim: remotely triggerable buffer overflow in string_vformat()
Summary: CVE-2019-16928 exim: remotely triggerable buffer overflow in string_vformat()
Alias: CVE-2019-16928
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
Depends On: 1756933 1756934
Blocks: 1756931
TreeView+ depends on / blocked
Reported: 2019-09-30 09:00 UTC by Tomas Hoger
Modified: 2019-09-30 12:45 UTC (History)
4 users (show)

Fixed In Version: exim 4.92.3
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Last Closed: 2019-09-30 12:45:34 UTC

Attachments (Terms of Use)

Description Tomas Hoger 2019-09-30 09:00:57 UTC
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:


Upstream commit:


The issue was fixed upstream in version 4.92.3.

Comment 1 Tomas Hoger 2019-09-30 09:03:49 UTC
External References:


Comment 2 Tomas Hoger 2019-09-30 09:04:11 UTC
Created exim tracking bugs for this issue:

Affects: epel-all [bug 1756934]
Affects: fedora-all [bug 1756933]

Comment 3 Tomas Hoger 2019-09-30 09:10:32 UTC
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.

Comment 5 Tomas Hoger 2019-09-30 10:49:43 UTC
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.


Comment 6 Product Security DevOps Team 2019-09-30 12:45:34 UTC
This bug is now closed. Further updates for individual products will be reflected on the CVE page(s):


Note You need to log in before you can comment on or make changes to this bug.