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PatchSiren cyber security CVE debrief

CVE-2026-39373 Latchset CVE debrief

CVE-2026-39373 is a vulnerability in JWCrypto, a Python library for implementing JWK, JWS, and JWE specifications. The vulnerability allows an unauthenticated attacker to 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, leading to potential memory exhaustion on memory-constrained systems. Users of JWCrypto library, especially those using versions prior to 1.5.7, should be aware of this vulnerability and take necessary precautions to prevent potential memory exhaustion attacks.

Vendor
Latchset
Product
Jwcrypto
CVSS
MEDIUM 5.3
CISA KEV
Not listed in stored evidence
Original CVE published
2026-04-07
Original CVE updated
2026-07-24
Advisory published
2026-04-07
Advisory updated
2026-07-24

Who should care

Users of JWCrypto library, especially those using versions prior to 1.5.7, should be aware of this vulnerability and take necessary precautions to prevent potential memory exhaustion attacks. System administrators and security teams should review system configurations and monitor for potential memory exhaustion attacks.

Technical summary

The vulnerability exists in JWCrypto's handling of JWE tokens with ZIP compression. An attacker can send a crafted token that, when decompressed, can exceed the 250KB input limit and potentially cause memory exhaustion. The vulnerability is fixed in version 1.5.7. Users of JWCrypto library, especially those using versions prior to 1.5.7, should be aware of this vulnerability and take necessary precautions to prevent potential memory exhaustion attacks.

Defensive priority

Medium

Recommended defensive actions

  • Upgrade to JWCrypto version 1.5.7 or later
  • Implement input validation and size limits for JWE tokens
  • Monitor system memory usage and implement alerting for potential memory exhaustion
  • Consider implementing compensating controls, such as rate limiting or IP blocking, to prevent potential attacks
  • Review system configurations for potential vulnerabilities
  • Track exceptions and retest remediated assets
  • Check relevant monitoring, detection, and logs for exposed assets that need extra review

Evidence notes

The vulnerability is described in the CVE record and the NVD detail page. The patch for CVE-2024-28102 is mentioned as limiting input token size to 250KB but not validating decompressed output size. An unauthenticated attacker can cause memory exhaustion on memory-constrained systems by sending crafted JWE tokens with ZIP compression. A token under the 250KB input limit can decompress to approximately 100MB. Users should verify system configurations and monitor for potential memory exhaustion attacks.

Sources and references

Verified primary and authoritative sources

  • CVE-2026-39373 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2026-39373

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2026-39373 NVD vulnerability detail

    Publisher, destination, and source semantics verified

    URL: https://nvd.nist.gov/vuln/detail/CVE-2026-39373

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

Supplemental references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.