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Fencer Vulns
critical 9.8

CVE-2021-33912 json

libspf2 before 1.2.11 has a four-byte heap-based buffer overflow that might allow remote attackers to execute arbitrary code (via an unauth…

published 2022-01-19 4 y ago modified 2026-06-17 4 mo ago also EUVD-2021-20584

cvss
9.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
9.6%
EPSS 9.6% chance of exploitation in 30 days, percentile 95%
public exploits
0
none known

Summary

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.

Patch / fix

  • libspf2_project libspf2 1.2.11
  • libspf2 Debian 14, Debian 13, Debian 12 1.2.10-7.1

debian advisories DEBIAN-CVE-2021-33912

  • libspf2 Ubuntu 20.04 LTS 1.2.10-7+deb9u2build0.20.04.1
  • libspf2 Ubuntu Pro 16.04 LTS 1.2.10-6ubuntu0.1~esm2
  • libspf2 Ubuntu Pro 18.04 LTS 1.2.10-7ubuntu0.18.04.1~esm1

ubuntu advisories UBUNTU-CVE-2021-33912

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • libspf2 Alpine 3.24, Alpine 3.23, Alpine 3.22 +8 more 1.2.11-r0

alpine advisories ALPINE-CVE-2021-33912

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-33912 updated

libspf2: Four-byte heap-based buffer overflow in SPF_record_expand_data in spf_expand.c

  • Red Hat All currently supported Red Hat products
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

Exploit prediction

9.64% chance of exploitation in the next 30 days, higher than 95% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • nathanielbennett.com https://nathanielbennett.com/blog/libspf2-cve-jan-2022-disclosure referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
NVD 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 2.0 9.3 AV:N/AC:M/Au:N/C:C/I:C/A:C

Classification

Weakness

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.