Token forgery via non-constant-time HMAC comparison
Published Jul 17, 2026 · Updated Jul 17, 2026
Observable timing discrepancy in Mojo::JWT before 1.02 allows remote attackers to recover HMAC signatures and forge tokens. The decode() method compares a supplied symmetric signature with the recomputed HMAC through Perl's early-exit eq operator, exposing matching-prefix length in response timing. Exploitation requires an application to decode attacker-supplied tokens repeatedly through a measurable remote path; a recovered signature permits forged tokens with claims accepted under the shared key.
Summary
What happened
Observable timing discrepancy in Mojo::JWT before 1.02 allows remote attackers to recover HMAC signatures and forge tokens. The decode() method compares a supplied symmetric signature with the recomputed HMAC through Perl's early-exit eq operator, exposing matching-prefix length in response timing. Exploitation requires an application to decode attacker-supplied tokens repeatedly through a measurable remote path; a recovered signature permits forged tokens with claims accepted under the shared key.
The record
- CVE
- CVE-2026-9537
- Published
- Jul 17, 2026
- Updated
- Jul 17, 2026
- Vendor
- Joel Berger
- Product
- Mojo::JWT
- Classifications
- CWE-208, T1550.001
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jul 17, 2026CVE publishedPublication date reported by the CVE source.
- Jul 17, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=0 <1.02
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Public exploit references
No public exploit references are available in this record.
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo