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Message-ID: <9cf95a36-fa06-4a05-a491-f44de77b17b3@cpansec.org>
Date: Fri, 17 Jul 2026 16:31:19 +0100
From: Robert Rothenberg <rrwo@...nsec.org>
To: cve-announce@...urity.metacpan.org, oss-security@...ts.openwall.com
Subject: CVE-2026-9537: Mojo::JWT versions before 1.02 for Perl verify HMAC
signatures with a non-constant-time string comparison
========================================================================
CVE-2026-9537 CPAN Security Group
========================================================================
CVE ID: CVE-2026-9537
Distribution: Mojo-JWT
Versions: before 1.02
MetaCPAN: https://metacpan.org/dist/Mojo-JWT
VCS Repo: http://github.com/jberger/Mojo-JWT
Mojo::JWT versions before 1.02 for Perl verify HMAC signatures with a
non-constant-time string comparison
Description
-----------
Mojo::JWT versions before 1.02 for Perl verify HMAC signatures with a
non-constant-time string comparison.
The decode() method compares the supplied signature to the recomputed
HMAC with Perl's eq operator, which stops at the first differing byte,
so the comparison time varies with the number of matching leading
bytes.
A caller that decodes attacker supplied tokens leaks the expected
signature through this timing variation, which can be aggregated over
many requests to recover the signature and forge a token.
Problem types
-------------
- CWE-208 Observable Timing Discrepancy
Solutions
---------
Upgrade to Mojo-JWT 1.02, which compares signatures with the
constant-time Mojo::Util::secure_compare.
References
----------
https://github.com/jberger/Mojo-JWT/commit/b8aefb846613e44b5b12bc170898ffd5b05094a2.patch
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