[17205] in Kerberos-V5-bugs
[krbdev.mit.edu #9251] git commit
daemon@ATHENA.MIT.EDU (Greg Hudson via RT)
Mon Nov 9 11:59:48 2026
From: "Greg Hudson via RT" <rt-comment@krbdev.mit.edu>
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Date: Mon, 09 Nov 2026 11:59:43 -0500
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Mon Nov 09 11:59:43 2026: Request 9251 was acted upon.
Transaction: Ticket created by ghudson@mit.edu
Queue: krb5
Subject: git commit
Owner: ghudson@mit.edu
Requestors:
Status: new
Ticket <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.
https://github.com/krb5/krb5/commit/cf44b0658832871f739d5074e7d27288b2718bfb
Author: Greg Hudson <ghudson@mit.edu>
Commit: cf44b0658832871f739d5074e7d27288b2718bfb
Branch: master
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(-)
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