[31657] in CVS-changelog-for-Kerberos-V5
krb5 commit [krb5-1.22]: Check for keyed checksums in CAMMAC verifiers
daemon@ATHENA.MIT.EDU (ghudson@mit.edu)
Mon Nov 9 12:00:56 2026
From: ghudson@mit.edu
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Date: Mon, 9 Nov 2026 12:00:41 -0500 (EST)
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https://github.com/krb5/krb5/commit/d97f92d1afd8c44b84c43ef16eb3eb1d7ed879b4
commit d97f92d1afd8c44b84c43ef16eb3eb1d7ed879b4
Author: Greg Hudson <ghudson@mit.edu>
Date: Sun Aug 2 21:39:23 2026 -0400
Check for keyed checksums in CAMMAC verifiers
In libkrb5's check_svcver() and in the KDC's cammac_check_kdcver(),
return an error if the verifier uses an unkeyed checksum.
CVE-2026-71199:
In MIT krb5 release 1.14 and later (since authentication indicator
support was added), an authenticated attacker can bypass
authentication indicator requirements using an unkeyed checksum in the
CAMMAC authdata container. Discovered by Claude and Ada Logics, and
by Alejandro Pacheco.
(cherry picked from commit 18142c9c3a3c2e16d8469aff342b02a28f0b468c)
ticket: 9228
version_fixed: 1.22.3
src/kdc/cammac.c | 2 +-
src/lib/krb5/krb/cammac_util.c | 2 ++
2 files changed, 3 insertions(+), 1 deletion(-)
diff --git a/src/kdc/cammac.c b/src/kdc/cammac.c
index df5fe966f..c0d5b6f66 100644
--- a/src/kdc/cammac.c
+++ b/src/kdc/cammac.c
@@ -144,7 +144,7 @@ cammac_check_kdcver(krb5_context context, krb5_cammac *cammac,
memset(&tgtkey, 0, sizeof(tgtkey));
- if (ver == NULL)
+ if (ver == NULL || !krb5_c_is_keyed_cksum(ver->checksum.checksum_type))
goto cleanup;
/* Fetch the krbtgt key indicated by the KDC verifier. Only allow the
diff --git a/src/lib/krb5/krb/cammac_util.c b/src/lib/krb5/krb/cammac_util.c
index ab9da05a7..32748e4ae 100644
--- a/src/lib/krb5/krb/cammac_util.c
+++ b/src/lib/krb5/krb/cammac_util.c
@@ -44,6 +44,8 @@ check_svcver(krb5_context context, const krb5_cammac *cammac,
if (ver == NULL)
return EINVAL;
+ if (!krb5_c_is_keyed_cksum(ver->checksum.checksum_type))
+ return KRB5KRB_AP_ERR_BAD_INTEGRITY;
ret = encode_krb5_authdata(cammac->elements, &der_authdata);
if (ret)
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