What is CVE-2017-16943?

CVE-2017-16943 is a critical-severity vulnerability in Exim, classified under Use After Free. CVSS score: 9.8/10. Published 2017-11-25.

How severe is CVE-2017-16943?

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

Is CVE-2017-16943 known to be exploited?

10 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.

Use After Free in Exim

CVE-2017-16943

The receive_msg function in receive.c in the SMTP daemon in Exim 4.88 and 4.89 allows remote attackers to execute arbitrary code or cause a denial of service (use-after-free) via vectors involving BDAT commands.

Vulnerability class: Use-After-Free

Published 2017-11-25 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 9.8 (Critical). Vector: CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.471 (98.8th percentile), scored 2026-10-19.

Moderate probability of exploitation in the next 30 days — watch for active exploitation reports. 99th percentile — 98.8% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.467 · newest: 0.471 · change: +0.004

Affected products

Exim — versions 4.88, 4.89
Debian Linux — versions 9.0

Weakness classification (CWE)

CWE-416 — Use After Free

Public proof-of-concept exploits

References

www.securitytracker.com/id/1039872 (VDB Entry, Third Party Advisory, vdb-entry)
lists.exim.org/lurker/message/20171125.034842.d1d75cac.en.html (Mailing List)
git.exim.org/exim.git/commit/4090d62a4b25782129cc1643596dc2f6e8f63bde (Patch)
openwall.com/lists/oss-security/2017/11/25/3 (Mailing List)
github.com/LetUsFsck/PoC-Exploit-Mirror/tree/master/CVE-2017-16944 (Exploit)
openwall.com/lists/oss-security/2017/11/25/1 (Mailing List)
git.exim.org/exim.git/commitdiff/4e6ae6235c68de243b1c2419027472d7659aa2b4 (Patch)
openwall.com/lists/oss-security/2017/11/25/2 (Mailing List)
www.debian.org/security/2017/dsa-4053 (vendor-advisory, Third Party Advisory)
bugs.exim.org/show_bug.cgi (Exploit, Issue Tracking)

Frequently asked questions

What is CVE-2017-16943?: CVE-2017-16943 is a critical-severity vulnerability in Exim, classified under Use After Free. CVSS score: 9.8/10. Published 2017-11-25.
How severe is CVE-2017-16943?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2017-16943 known to be exploited?: 10 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.