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Vulnerability record · CVE-2021-33912 · published 19 January 2022

CVE-2021-33912: Libspf2 project libspf2 out-of-bounds write vulnerability

LLibspf2 Project · Libspf2

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.

9.8 CVSS 3.1 Critical EPSS 9.6% · top 4.7% CWE-787 · Out-of-bounds write
9.8CVSS 3.1 base score, v2 9.3
9.6%EPSS exploitation probability, 30 days
NoNot in CISA KEV
2Affected product versions listed by NVD
8References, 2 tagged exploit
17 Jun 2026Last modified by NVD

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.

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

Affected products

2 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/shevek/libspf2/tree/8131fe140704eaae695e76b5cd09e39bd1dd220b Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/01/msg00015.html Mailing ListThird Party Advisory
https://nathanielbennett.com/blog/libspf2-cve-jan-2022-disclosure ExploitThird Party Advisory
https://security.gentoo.org/glsa/202401-22
https://github.com/shevek/libspf2/tree/8131fe140704eaae695e76b5cd09e39bd1dd220b Third Party Advisory
https://lists.debian.org/debian-lts-announce/2022/01/msg00015.html Mailing ListThird Party Advisory
https://nathanielbennett.com/blog/libspf2-cve-jan-2022-disclosure ExploitThird Party Advisory
https://security.gentoo.org/glsa/202401-22

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Source: NIST National Vulnerability Database (record CVE-2021-33912), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.