CVE-2026-11850

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.

Red Hat rates this issue as Moderate impact. In krb5's LDAP KDB plugin, berval2tl_data() subtracts two from a BER value length without checking it is at least two. A malicious or compromised LDAP KDB backend returning krbExtraData with length 0 or 1 causes unsigned underflow and a large heap out-of-bounds read when the KDC or kadmind loads principal data. Exploitation requires compromise of or write access to the LDAP backend used as the Kerberos database. Deployments using file-based KDB backends rather than LDAP are not affected by this code path.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.

Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base or stability.