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MEDIUM severity

Non-constant time HMAC comparisonGHSA-fj6f-6933-839j

MEDIUMFix: jenkinsci/jenkins@6f35dbb

GHSA-fj6f-6933-839j is a medium-severity (CVSS 5.3) CWE-203 vulnerability in org.jenkins-ci.main:jenkins-core. A fix is available for org.jenkins-ci.main:jenkins-core — see the affected versions and patch details below.

Also known asBIT-jenkins-2020-2102CVE-2020-2102
Published
Updated
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Nov 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.4%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs72th percentile — riskier than 72% of all scored CVEsHighest risk
0.90%1.27%1.65%2.02%1.5%1.4%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

2 pkgs affected
☕org.jenkins-ci.main:jenkins-core☕org.jenkins-ci.main:jenkins-core

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

Description

Jenkins 2.218 and earlier, LTS 2.204.1 and earlier does not use a constant-time comparison when checking whether two HMACs are equal. This could potentially allow attackers to use statistical methods to obtain a valid HMAC for an attacker-controlled input value.

Jenkins 2.219, LTS 2.204.2 now uses a constant-time comparison when validating HMACs.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
☕Mavenorg.jenkins-ci.main:jenkins-coreall versions2.204.2org.jenkins-ci.main:jenkins-core:2.204.2
☕Mavenorg.jenkins-ci.main:jenkins-core≥ 2.205&&< 2.2192.219org.jenkins-ci.main:jenkins-core:2.219

Affected Products

1 product · 2 configurations
Application
jenkinsjenkins
≤ 2.218
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 org.jenkins-ci.main:jenkins-core, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update org.jenkins-ci.main:jenkins-core to 2.204.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-fj6f-6933-839j 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.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate
ProductFixed inAdvisory
Red Hat OpenShift Container Platform 3.11atomic-enterprise-service-catalog-1:3.11.170-1.git.1.91db82e.el7RHBA-2020:0402
Red Hat OpenShift Container Platform 4.3jenkins-0:2.204.2.1583446818-1.el7RHBA-2020:0675
Red Hat OpenShift Container Platform 4.4openshift4/ose-aws-machine-controllers:v4.4.0-202004261927RHBA-2020:0581
Red Hat OpenShift Container Platform 4.5openshift4/ose-aws-machine-controllers:v4.5.0-202007012112.p0RHBA-2020:2409

Frequently Asked Questions

Jenkins 2.218 and earlier, LTS 2.204.1 and earlier does not use a constant-time comparison when checking whether two HMACs are equal. This could potentially allow attackers to use statistical methods to obtain a valid HMAC for an attacker-controlled input value. Jenkins 2.219, LTS 2.204.2 now uses a constant-time comparison when validating HMACs.
O3 Security · Impact-Aware SCA

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Non-constant time HMAC comparison (Medium 5.3)