What is CVE-2020-28024?

CVE-2020-28024 is a critical-severity vulnerability in Exim, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2021-05-06.

How severe is CVE-2020-28024?

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

Is CVE-2020-28024 known to be exploited?

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

Buffer overflow in Exim

CVE-2020-28024

Exim 4 before 4.94.2 allows Buffer Underwrite that may result in unauthenticated remote attackers executing arbitrary commands, because smtp_ungetc was only intended to push back characters, but can actually push back non-character error codes such as EOF.

Vulnerability class: Buffer Overflow

Published 2021-05-06 · 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: 0.042 (90.7th percentile), scored 2026-10-19.

Low probability of exploitation in the next 30 days, but still tracked. 91st percentile — 90.7% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.042 · newest: 0.042 · change: 0.000

Affected products

Exim

Weakness classification (CWE)

CWE-787 — Out-of-bounds Write

Public proof-of-concept exploits

References

www.exim.org/static/doc/security/CVE-2020-qualys/CVE-2020-28024-UNGET.txt (Third Party Advisory)

Frequently asked questions

What is CVE-2020-28024?: CVE-2020-28024 is a critical-severity vulnerability in Exim, classified under Out-of-bounds Write. CVSS score: 9.8/10. Published 2021-05-06.
How severe is CVE-2020-28024?: Critical severity. CVSS v3 base score is 9.8 out of 10.
Is CVE-2020-28024 known to be exploited?: 5 public proof-of-concept repositories are indexed. Not currently listed in the CISA KEV catalog.