CVE-2026-9537
MEDIUMDescription
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.
How to fix
TridentStack Control can deploy fixes like this automatically across your Windows, macOS, and Linux fleet. See how it works
Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.
CVSS v3 Vector
Exploitability
Impact
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
Exploit Intelligence
Low risk: more likely to be exploited than 25% of all known CVEs.
References
Related Vulnerabilities
Other CWE-208 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2019-9494 | Medium | 5.9 | 3.9% | - | Fix |
| CVE-2019-16782 | Medium | 6.3 | 3.7% | - | Fix |
| CVE-2025-53940 | Unscored | - | 2.8% | - | - |
| CVE-2020-1926 | Medium | 5.9 | 2.5% | - | Fix |
| CVE-2021-43298 | Critical | 9.8 | 2.3% | - | Fix |
| CVE-2024-29995 | High | 8.1 | 1.5% | - | Fix |
Common questions
How do I fix CVE-2026-9537?
Upgrade libmojo-jwt-perl on debian unstable to 1.02-1 or later.
Is CVE-2026-9537 being actively exploited?
Not that we know of. CVE-2026-9537 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.32% is the estimated probability that it will be exploited in the next 30 days. That is higher than 25% of all scored CVEs.
How severe is CVE-2026-9537?
CVE-2026-9537 has a CVSS v3 base score of 5.3, rated medium. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
What does CVE-2026-9537 affect?
Published advisories record a fix for libmojo-jwt-perl (Debian). Only products with a sourced advisory are listed, so treat this as what we can cite rather than a complete inventory.
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Markdown
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-07-20.