[17237] in Kerberos-V5-bugs
[krbdev.mit.edu #9251] git commit
daemon@ATHENA.MIT.EDU (Greg Hudson via RT)
Mon Nov 9 12:02:55 2026
From: "Greg Hudson via RT" <rt@krbdev.mit.edu>
In-Reply-To:
Message-ID: <rt-4.4.3-2-3131593-1794243770-1235.9251-5-0@mit.edu>
To: "AdminCc of krbdev.mit.edu Ticket #9251":;
Date: Mon, 09 Nov 2026 12:02:50 -0500
MIME-Version: 1.0
Reply-To: rt@krbdev.mit.edu
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Errors-To: krb5-bugs-bounces@mit.edu
<URL: https://krbdev.mit.edu/rt/Ticket/Display.html?id=9251 >
Prevent KDC read overrun in ASN.1 decoder
The KDC decodes requests using the libkrb5 ASN.1 DER decoder, but
obtains pointers to subsets of the encoding (such as the KDC-REQ-BODY)
via its own fetch_asn1_field(). This utility function does not
consider the input length, assumes the tag identifier is a single
byte, and supports indefinite length encoding. The libkrb5 decoder
accepts multi-byte tag identifiers and does not enforce minimality of
tag identifier encoding. A request packet crafted using a non-minimal
tag identifier can pass through the libkrb5 decoder, but fool
fetch_asn1_field() into indefinite length processing, which may send
it reading far beyond the bounds of the packet. Discovered by Claude
and Ada Logics.
In fetch_asn1_field(), error out if we see a tag identifier byte
indicating a multi-byte encoding. Also remove indefinite length
processing; the libkrb5 decoder stopped supporting it in commit
d9443a58cd364349b7d764f4e997f3af7d979a87.
CVE-2026-107364:
In all released versions of MIT krb5, an unauthenticated attacker can
cause a KDC process to perform a large read overrun, likely causing
the process to terminate.
(cherry picked from commit cf44b0658832871f739d5074e7d27288b2718bfb)
https://github.com/krb5/krb5/commit/4e941239157dd30969998f33db0708b8d297bd41
Author: Greg Hudson <ghudson@mit.edu>
Commit: 4e941239157dd30969998f33db0708b8d297bd41
Branch: krb5-1.22
src/kdc/kdc_util.c | 33 ++++++-------------------------
src/tests/Makefile.in | 1 +
src/tests/t_cve-2026-107364.py | 45 ++++++++++++++++++++++++++++++++++++++++++
3 files changed, 52 insertions(+), 27 deletions(-)
_______________________________________________
krb5-bugs mailing list
krb5-bugs@mit.edu
https://mailman.mit.edu/mailman/listinfo/krb5-bugs
