CVE-2026-39373
MEDIUMDescription
JWCrypto implements JWK, JWS, and JWE specifications using python-cryptography. Prior to 1.5.7, an unauthenticated attacker can exhaust server memory by sending crafted JWE tokens with ZIP compression. The existing patch for CVE-2024-28102 limits input token size to 250KB but does not validate the decompressed output size. An unauthenticated attacker can cause memory exhaustion on memory-constrained systems. A token under the 250KB input limit can decompress to approximately 100MB. This vulnerability is fixed in 1.5.7.
How to fix
This vulnerability affects an unusually large number of packages. The highest-confidence fixes are shown above; the full list is longer. Check the referenced advisories for complete coverage.
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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:N/A:L
Exploit Intelligence
Low risk: more likely to be exploited than 22% of all known CVEs.
References
Related Vulnerabilities
Other CWE-409 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2026-49975 | High | 7.5 | 34% | - | Fix |
| CVE-2026-21441 | High | 7.5 | 3.0% | - | Fix |
| CVE-2024-43499 | High | 7.5 | 2.6% | - | Fix |
| CVE-2024-28180 | Medium | 4.3 | 2.0% | - | Fix |
| CVE-2017-16129 | Medium | 5.9 | 1.8% | - | Fix |
| CVE-2022-29225 | High | 7.5 | 1.6% | - | Fix |
Common questions
How do I fix CVE-2026-39373?
Published advisories record a fix for 241 affected products. The "How to fix" section on this page lists the fixed version and source advisory for each one, so apply the entry matching what you actually run.
Is CVE-2026-39373 being actively exploited?
Not that we know of. CVE-2026-39373 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 0.29% is the estimated probability that it will be exploited in the next 30 days. That is higher than 22% of all scored CVEs.
How severe is CVE-2026-39373?
CVE-2026-39373 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-2026-39373 affect?
Published advisories record a fix for python-jwcrypto (Amazon), python3-jwcrypto (Amazon), python-jwcrypto (Debian), aap-metrics-utility (Red Hat / RHEL), and 237 more. 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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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 2026-07-24.