What’s Vulnerable › Vulnerabilities

CVE-2021-33912

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 9.6% probability of exploitation in the next 30 days
• Public exploit or detection template: yes
• Published: 2022-01-19 · updated 2026-06-17
• Weakness: CWE-787

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.

Affected products

• Debian Linux: 9.0
• Exim libspf2: before 1.2.11 — fixed in 1.2.11

How to fix

Upgrade to a fixed version: Exim libspf2 1.2.11. Check the vendor advisory for mitigations.

References

• https://github.com/shevek/libspf2/tree/8131fe140704eaae695e76b5cd09e39bd1dd220b
• https://lists.debian.org/debian-lts-announce/2022/01/msg00015.html
• https://nathanielbennett.com/blog/libspf2-cve-jan-2022-disclosure
• https://security.gentoo.org/glsa/202401-22
• https://github.com/shevek/libspf2/tree/8131fe140704eaae695e76b5cd09e39bd1dd220b
• https://lists.debian.org/debian-lts-announce/2022/01/msg00015.html
• https://nathanielbennett.com/blog/libspf2-cve-jan-2022-disclosure
• https://security.gentoo.org/glsa/202401-22

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