What’s Vulnerable › Vulnerabilities

CVE-2021-33913

• 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 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 SPF_record_expand_data in spf_expand.c. The amount of overflowed data depends on the relationship between the length of an entire domain name and the length of its leftmost label. 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

• 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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