Session-signature disclosure via nonconstant HMAC comparison
Published Dec 9, 2025 · Updated Dec 11, 2025
A timing side channel in Plack::Middleware::Session before 0.17 allows remote attackers to infer HMAC signature bytes through cookie checks. Cookie.pm compares a computed signature with attacker-supplied cookie data using Perl's early-exit string equality operator, leaking match-length timing. A reachable PSGI application must use signed session cookies and permit repeated verification attempts; the bounded consequence is information leakage about a valid signature.
Summary
What happened
A timing side channel in Plack::Middleware::Session before 0.17 allows remote attackers to infer HMAC signature bytes through cookie checks. Cookie.pm compares a computed signature with attacker-supplied cookie data using Perl's early-exit string equality operator, leaking match-length timing. A reachable PSGI application must use signed session cookies and permit repeated verification attempts; the bounded consequence is information leakage about a valid signature.
The record
- CVE
- CVE-2013-10031
- Published
- Dec 9, 2025
- Updated
- Dec 11, 2025
- Vendor
- Tatsuhiko Miyagawa
- Product
- Plack::Middleware::Session
- Classifications
- CWE-1254
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Dec 9, 2025CVE publishedPublication date reported by the CVE source.
- Dec 11, 2025Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
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- Affected versionversion=0.01 <0.17
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
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Weakness, pattern, technique
Public exploit references
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Technologies
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