CVE-2026-11850

Name	CVE-2026-11850
Description	An integer underflow vulnerability was found in MIT krb5 in the berval2tl_data() function in plugins/kdb/ldap/libkdb_ldap/ldap_principal2.c. The function performs an unsigned subtraction (bv_len - 2) without a prior bounds check. When bv_len is 0 or 1, the subtraction wraps to a large value which is then truncated to uint16_t, yielding 0xFFFE (65534) or 0xFFFF (65535). The subsequent malloc succeeds and memcpy reads up to 65534 bytes from a 0-1 byte buffer, resulting in a heap out-of-bounds read. The attack vector involves a malicious or compromised LDAP KDB backend returning a krbExtraData attribute with bv_len < 2, triggering the underflow when the KDC or kadmind reads principal data.
Source	CVE (at NVD; CERT, ENISA, LWN, oss-sec, fulldisc, Debian ELTS, Red Hat, Ubuntu, Gentoo, SUSE bugzilla/CVE, GitHub advisories/code/issues, web search, more)
Debian Bugs	1139821

Vulnerable and fixed packages

The table below lists information on source packages.

Source Package	Release	Version	Status
krb5 (PTS)	bullseye	1.18.3-6+deb11u5	vulnerable
	bullseye (security)	1.18.3-6+deb11u8	vulnerable
	bookworm	1.20.1-2+deb12u4	vulnerable
	bookworm (security)	1.20.1-2+deb12u5	vulnerable
	trixie	1.21.3-5	vulnerable
	trixie (security)	1.21.3-5+deb13u1	vulnerable
	forky, sid	1.22.1-2.1	vulnerable

The information below is based on the following data on fixed versions.

Package	Type	Release	Fixed Version	Urgency	Origin	Debian Bugs
krb5	source	(unstable)	(unfixed)			1139821

Notes

[trixie] - krb5 <no-dsa> (Minor issue)
[bullseye] - krb5 <postponed> (Minor issue)
https://krbdev.mit.edu/rt/Ticket/Display.html?id=9206
https://github.com/krb5/krb5/commit/2a5fd83d4436583f2ddc0e193269a4d800ee45c4