CVE-2021-33912

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.