Vulnerability · Published Apr 7, 2026 · Assigned by GitHub_M
CVE-2026-39373JWCrypto: JWE ZIP decompression bomb
Medium 5.3
In plain English
A medium-severity security flaw in jwcrypto from latchset. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.3% (higher than 23% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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.
Affected packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | python3-jwcrypto | 1.5.6-5.el10_2 | ALSA-2026:19042 |
| AlmaLinux:9 | python3-jwcrypto | 1.5.6-3.el9_8 | ALSA-2026:19197 |
| Debian:12 | python-jwcrypto | no fix listed | DEBIAN-CVE-2026-39373 |
| Debian:13 | python-jwcrypto | 1.5.6-1.1~deb13u1 | DEBIAN-CVE-2026-39373 |
| Debian:14 | python-jwcrypto | 1.5.6-1.1 | DEBIAN-CVE-2026-39373 |
| PyPI | jwcrypto | 1.5.7 | GHSA-fjrm-76x2-c4q4 |
| PyPI | jwcrypto | 1.5.7 | PYSEC-2026-70 |
| Rocky Linux:10 | python-jwcrypto | 0:1.5.6-5.el10_2 | RLSA-2026:19042 |
| Rocky Linux:9 | python-jwcrypto | 0:1.5.6-3.el9_8 | RLSA-2026:19197 |
| Ubuntu:22.04:LTS | python-jwcrypto | no fix listed | UBUNTU-CVE-2026-39373 |
| Ubuntu:24.04:LTS | python-jwcrypto | no fix listed | UBUNTU-CVE-2026-39373 |
| Ubuntu:25.10 | python-jwcrypto | no fix listed | UBUNTU-CVE-2026-39373 |
| Ubuntu:26.04:LTS | python-jwcrypto | no fix listed | UBUNTU-CVE-2026-39373 |
| Ubuntu:26.10 | python-jwcrypto | no fix listed | UBUNTU-CVE-2026-39373 |
Affected products (as reported)
Weakness: CWE-409 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
References
- https://github.com/latchset/jwcrypto/security/advisories/GHSA-fjrm-76x2-c4q4 x_refsource_CONFIRM