CVE-2026-11850: Krb5: krb5: integer underflow in berval2tl_data() leads to heap out-of-bounds read

Severity: medium (CVSS 5.0 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.3% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-06-11 · updated 2026-10-31
Weakness: CWE-191

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.

Affected products

Red Hat OpenShift Container Platform 4.18: all versions
Red Hat Enterprise Linux 10: all versions
Red Hat Enterprise Linux 6: all versions
Red Hat Enterprise Linux 7: all versions
Red Hat Enterprise Linux 8: all versions
Red Hat Enterprise Linux 9: all versions
Red Hat Hardened Images: all versions — fixed in 1.22.2-8.hum1
Red Hat OpenShift Container Platform 5: all versions

How to fix

Upgrade to a fixed version: Red Hat Hardened Images 1.22.2-8.hum1. Check the vendor advisory for mitigations.

References

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