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MEDIUM severity

CVE-2018-1000539 — json-jwt

MEDIUMFix: nov/json-jwt#62

CVE-2018-1000539 is a medium-severity (CVSS 5.3) CWE-347 vulnerability in json-jwt. A fix is available for json-jwt — see the affected versions and patch details below.

Json-jwt did not verify the cryptographic signature for data

Also known asGHSA-mj4x-wcxf-hm8x
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 6, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
0.8%probability of exploitation in next 30 days
Lower Risk-0.01%
Lower risk than most CVEs56th percentile — riskier than 56% of all scored CVEsHighest risk
0.00%0.43%0.85%1.28%0.1%0.8%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
💎json-jwt

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.

Description

The json-jwt rubygem version >= 0.5.0 && < 1.9.4 contains a CWE-347: Improper Verification of Cryptographic Signature vulnerability in Decryption of AES-GCM encrypted JSON Web Tokens that can result in Attacker can forge a authentication tag. This attack appear to be exploitable via network connectivity. This vulnerability appears to have been fixed in 1.9.4 and later.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
💎RubyGemsjson-jwt≥ 0.5.1&&< 1.9.41.9.4bundle update json-jwt --conservative

Affected Products

1 product · 1 configurations
Application
json-jwtjson-jwt_project
≥ 0.5.0 && < 1.9.4
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for json-jwt, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update json-jwt to 1.9.4 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2018-1000539 is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Frequently Asked Questions

The json-jwt rubygem version >= 0.5.0 && < 1.9.4 contains a CWE-347: Improper Verification of Cryptographic Signature vulnerability in Decryption of AES-GCM encrypted JSON Web Tokens that can result in Attacker can forge a authentication tag. This attack appear to be exploitable via network connectivity. This vulnerability appears to have been fixed in 1.9.4 and later.
O3 Security · Impact-Aware SCA

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CVE-2018-1000539: json-jwt — Fixed in 1.9.4