What is CVE-2019-16928?

CVE-2019-16928 is a critical-severity vulnerability in Exim, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2019-09-27.

How severe is CVE-2019-16928?

Critical severity. CVSS v3 base score is 9.8 out of 10.

Is CVE-2019-16928 known to be exploited?

Yes. CVE-2019-16928 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-03-03), indicating it is being actively exploited. 10 public proof-of-concept repositories are indexed.

Buffer overflow in Exim

CVE-2019-16928

Exim 4.92 through 4.92.2 allows remote code execution, a different vulnerability than CVE-2019-15846. There is a heap-based buffer overflow in string_vformat in string.c involving a long EHLO command.

Vulnerability class: Buffer Overflow

Published 2019-09-27 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.416 (98.7th percentile), scored 2026-10-18.

Moderate probability of exploitation in the next 30 days — watch for active exploitation reports. 99th percentile — 98.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.416 · newest: 0.416 · change: 0.000

Affected products

Exim
Canonical Ubuntu Linux — versions 19.04
Debian Linux — versions 10.0
Fedoraproject Fedora — versions 29, 30, 31

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

CISA KEV (Known Exploited Vulnerabilities)

This CVE is on the CISA KEV catalog, added on 2022-03-03. CISA KEV inclusion means CISA has confirmed in-the-wild exploitation; US federal agencies are required to remediate within a published due date.

BOD 22-01 due date: 2022-03-17.

Required action: Apply updates per vendor instructions.

Public proof-of-concept exploits

References

lists.exim.org/lurker/message/20190927.032457.c1044d4c.en.html (Vendor Advisory)
bugs.exim.org/show_bug.cgi (Patch, Issue Tracking, Vendor Advisory)
git.exim.org/exim.git/commit/478effbfd9c3cc5a627fc671d4bf94d13670d65f (Patch)
www.openwall.com/lists/oss-security/2019/09/28/1 (mailing-list, Exploit, Mailing List, Third Party Advisory, Mitigation)
www.openwall.com/lists/oss-security/2019/09/28/2 (mailing-list, Exploit, Mailing List, Third Party Advisory)
www.openwall.com/lists/oss-security/2019/09/28/3 (mailing-list, Mailing List, Third Party Advisory)
www.debian.org/security/2019/dsa-4536 (vendor-advisory, Third Party Advisory)
usn.ubuntu.com/4141-1/ (vendor-advisory, Third Party Advisory)
www.openwall.com/lists/oss-security/2019/09/28/4 (mailing-list, Mailing List, Third Party Advisory)
seclists.org/bugtraq/2019/Sep/60 (mailing-list, Mailing List, Third Party Advisory)

Frequently asked questions

What is CVE-2019-16928?: CVE-2019-16928 is a critical-severity vulnerability in Exim, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2019-09-27.
How severe is CVE-2019-16928?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2019-16928 known to be exploited?: Yes. CVE-2019-16928 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2022-03-03), indicating it is being actively exploited. 10 public proof-of-concept repositories are indexed.