MITKRB5-SA-2026-001 MIT krb5 Security Advisory 2026-001 Original release: 2026-11-09 Last update: 2026-11-09 Topic: Multiple vulnerabilities fixed in patch 1.22.3 SUMMARY ======= Like many open source projects, MIT krb5 has faced greatly increased scrutiny over the past few months from researchers employing large language models. As a result, release 1.22.3 fixes many more vulnerabilities than a typical MIT krb5 patch release. This advisory discusses the combined impact of those vulnerabilities on unpatched components. AUTHORIZATION BYPASS ATTACKS ============================ An authenticated attacker can bypass authentication indicator enforcement by requesting a service ticket with fake CAMMAC authorization data. Updating to the 1.22.3 release on the KDC is sufficient to prevent this attack. An authenticated attacker can bypass an application server's PAC authorization data checks by requesting a service ticket with a fake PAC. Updating to the 1.22.3 release on either the KDC or the affected application server will prevent this attack. An authenticated attacker with administrative privileges can bypass the lockdown_keys attribute by using the password change protocol instead of the kadmin protocol to modify a principal's keys. The CVEs in this category include: CVE-2026-71199 CVE-2026-107884 CVE-2026-111423 DENIAL OF SERVICE ATTACKS ========================= The KDC, kadmind, and GSS-API application servers are all vulnerable to denial of service attacks by unauthenticated attackers. The CVEs in this category include: CVE-2026-40355 CVE-2026-40356 CVE-2026-71200 CVE-2026-107364 CVE-2026-107708 CVE-2026-107778 CVE-2026-112314 CVE-2026-112315 CVE-2026-112316 CVE-2026-112317 CVE-2026-112318 CVE-2026-112319 CVE-2026-112320 CVE-2026-112321 CVE-2026-112322 CVE-2026-112323 CVE-2026-119079 GSS-RPC USE OF UNVERIFIED SERVICE TYPE ====================================== Application servers using libgssrpc with RPCSEC_GSS protection may be vulnerable to an active network attack that fools the server into disabling cryptographic protection of RPC arguments and return values. The primary component affected by this vulnerability is kadmind, which serves the kadm5 and iprop RPC protocols. Using this vulnerability, an active network attacker on the path between a replica KDC and the primary KDC can cause kadmind to reveal the contents of an incremental update reply in plain text. This update may contain sensitive Kerberos database material. Any key information in the incremental update will be encrypted in the master key, but if the master password is not strong, a dictionary attack may reveal the unencrypted key data. Updating to the 1.22.3 release on the primary kadmin server is sufficient to prevent this attack. We believe that this vulnerability is not exploitable in the kadm5 protocol, because the kadmin client makes an INIT remote procedure call before issuing any substantive RPCs. Because only the server is fooled into disabling encryption, the client will abort the kadmin session when it tries to decode the INIT reply. We also considered scenarios where an attacker replays a modified copy of a recorded kadmin session, but we believe that the replay cache and the use of subkeys prevent this variant of the attack. The CVE in this category is CVE-2026-118380. WINDOWS CLIENT VULNERABILITIES ============================== Applications using leashdll are vulnerable to a buffer overflow (possibly leading to code execution) if the KDC supplies a very long prompt banner. Exploitating this vulnerability may be impossible because only the FAST OTP preauth mechanism permits large prompt banners, and the leashdll APIs do not set a FAST armor cache. If an application supplies principal names from an untrusted source to leashdll initial ticket functions (such as Leash_kinit_dlg()), an attacker could cause buffer overflows by supplying long names, possibly leading to code execution. On a Windows host with untrusted users, an attacker could potentially trick kfwlogon into setting ACL rights on a file of the attacker's choice via a hard link. On a Windows host with untrusted users, a user could create a krb5.ini file in the default per-machine location prior to Kerberos for Windows installation. This file would then be used by other users, allowing code execution via module loading. ACKNOWLEDGEMENTS ================ The following individuals and organizations contributed to the discovery of the vulnerabilities fixed in the 1.22.3 release: Arthur Chan Rahul Hoysala Alexandru-Ionut Jipa Cem Onat Karagun David Korczynski Erin Liman Tristan Madani Alejandro Pacheco Julien Rische Moritz Theile Rickey Visinski Ada Logics AISLE Anthropic AWS Security Deutsche Bank Red Hat Talence Security REVISION HISTORY ================ 2026-11-09 original release Copyright (C) 2026 Massachusetts Institute of Technology