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()
Keywords:
Status: CLOSED NOTABUG
Alias: CVE-2019-16928
Product: Security Response
Classification: Other
Component: vulnerability
Version: unspecified
Hardware: All
OS: Linux
urgent
urgent
Target Milestone: ---
Assignee: Red Hat Product Security
QA Contact:
URL:
Whiteboard:
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
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Environment:
Last Closed: 2019-09-30 12:45:34 UTC


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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:

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.

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

https://exim.org/static/doc/security/CVE-2019-16928.txt

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:

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.

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.

https://seclists.org/oss-sec/2019/q3/255

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):

https://access.redhat.com/security/cve/cve-2019-16928


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