CVE-2021-33912

Name: CVE-2021-33912
Creator: NVD / NIST
Published: 2022-01-19T18:15:07.783+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

CRITICALCVSS 9.8/10EPSS 9.64%

Last modified Jun 17, 2026

CVE-2021-33912 is a critical-severity vulnerability rated 9.8/10 on the CVSS scale. libspf2 before 1.2.11 has a four-byte heap-based buffer overflow that might allow remote attackers to execute arbitrary code (via an unauthenticated e-mail message from anywhere on the Internet) with a crafted SPF DNS record, because of incorrect sprintf usage in SPF_record_expand_data in spf_expand.c. The vulnerable code may be part of the supply chain of a site's e-mail infrastructure (e.g., with additional configuration, Exim can use libspf2; the Postfix web site links to unofficial patches for use of libspf2 with Postfix; older versions of spfquery relied on libspf2) but most often is not.. EPSS estimates a 9.64% chance of exploitation in the next 30 days.

Description

libspf2 before 1.2.11 has a four-byte heap-based buffer overflow that might allow remote attackers to execute arbitrary code (via an unauthenticated e-mail message from anywhere on the Internet) with a crafted SPF DNS record, because of incorrect sprintf usage in SPF_record_expand_data in spf_expand.c. The vulnerable code may be part of the supply chain of a site's e-mail infrastructure (e.g., with additional configuration, Exim can use libspf2; the Postfix web site links to unofficial patches for use of libspf2 with Postfix; older versions of spfquery relied on libspf2) but most often is not.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

9.64%

94.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-787

Affected Software

Vendor	Product	Versions
Libspf2 Project	Libspf2	< 1.2.11
Debian	Debian Linux	9.0

References

https://github.com/shevek/libspf2/tree/8131fe140704eaae695e76b5cd09e39bd1dd220bThird Party Advisory
https://lists.debian.org/debian-lts-announce/2022/01/msg00015.htmlMailing List, Third Party Advisory
https://nathanielbennett.com/blog/libspf2-cve-jan-2022-disclosureExploit, Third Party Advisory
https://security.gentoo.org/glsa/202401-22
https://github.com/shevek/libspf2/tree/8131fe140704eaae695e76b5cd09e39bd1dd220bThird Party Advisory
https://lists.debian.org/debian-lts-announce/2022/01/msg00015.htmlMailing List, Third Party Advisory
https://nathanielbennett.com/blog/libspf2-cve-jan-2022-disclosureExploit, Third Party Advisory
https://security.gentoo.org/glsa/202401-22

Timeline

Published: Jan 19, 2022
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-33912?

How severe is CVE-2021-33912?

CVE-2021-33912 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 9.64% probability of exploitation in the next 30 days.

How do I fix CVE-2021-33912?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-33912?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST