CVE-2026-39373 | JWCrypto: JWE ZIP decompression bomb

Exp

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.

Published: 2026-04-07 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-39373 is rated Exploit Available (50/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.29%). 1 public exploit reference(s) are indexed (Exploit-DB). Public exploits are available—assess exposure, apply mitigations, and prioritize patching.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Public exploit references (Exploit-DB) for CVE-2026-39373

EDB-ID Source Kind Published Link
— nvd_ref exploit_tag Exploit-DB ↗

Exploit prediction scoring system (EPSS) score for CVE-2026-39373

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.07% 0.29% +0.22%
2 2026-04-16 0.04% 0.07% +0.03%
3 2026-04-08 — 0.04% —

Full EPSS history (3 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-39373

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.3 3.1 MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:L)
Might cause slowdowns, glitches, or partial disruption—not a full brick.
 3.9 1.4 [email protected]

Weakness enumeration for CVE-2026-39373

GitHub Security Advisory for CVE-2026-39373

GHSA-fjrm-76x2-c4q4 · Severity: medium · Ecosystem: pip — JWCrypto: JWE ZIP decompression bomb

OS Trackers for CVE-2026-39373

vendor priority summary link
debian not yet assigned CVE-2026-39373 not yet assigned priority: Debian including 1 source packages (python-jwcrypto), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): open 5. https://security-tracker.debian.org/tracker/CVE-2026-39373
redhat medium — https://access.redhat.com/security/cve/CVE-2026-39373
suse high CVE-2026-39373 severity important: SUSE including 1 source package names (python3-jwcrypto-0.7-bp156.4.3.1), 2 product×package rows across 2 product lines (SUSE Package Hub 15 SP6, openSUSE Leap 15.6): Fixed 2. https://www.suse.com/security/cve/CVE-2026-39373/
ubuntu medium CVE-2026-39373 medium priority: Ubuntu including 1 source packages (python-jwcrypto), 7 status rows across 7 suites (bionic, focal, jammy, noble, questing, upstream, xenial): needs-triage 7. https://ubuntu.com/security/CVE-2026-39373

Affected software / configurations for CVE-2026-39373

Vendor Product Version Raw CPE
latchset jwcrypto < 1.5.7 cpe:2.3:a:latchset:jwcrypto:*:*:*:*:*:*:*:*

References for CVE-2026-39373

cvelogic Threat Intelligence