Inbound TCP Agent Protocol/3 authentication bypass in Jenkins

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

8.6 · CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

EPSS

• CVE-2020-2099: 1.01% estimated exploitation activity in the next 30 days; percentile 63.25 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Jenkins 2.213 and earlier, LTS 2.204.1 and earlier includes support for the Inbound TCP Agent Protocol/3 for communication between controller and agents. While this protocol has been deprecated in 2018 and was recently removed from Jenkins in 2.214, it could still easily be enabled in Jenkins LTS 2.204.1, 2.213, and older. This protocol incorrectly reuses encryption parameters which allow an unauthenticated remote attacker to determine the connection secret. This secret can then be used to connect attacker-controlled Jenkins agents to the Jenkins controller. Jenkins 2.204.2 no longer allows for the use of Inbound TCP Agent Protocol/3 by default. The system property jenkins.slaves.JnlpSlaveAgentProtocol3.ALLOWUNSAFE can be set to true to allow enabling the Inbound TCP Agent Protocol/3 in Jenkins 2.204.2, but doing so is strongly discouraged. Inbound TCP Agent Protocol/3 was removed completely from Jenkins 2.214 and will not be part of Jenkins LTS after the end of the 2.204.x line.

Published by the source

24 May 2022, 17:07 UTC

Last modified by the source

13 Dec 2023, 11:54 UTC

Source last checked

26 Oct 2026, 16:20 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-qp4f-2w67-c8hw

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# Patch Next advisory brief: CVE-2020-2099

Advisory: Inbound TCP Agent Protocol/3 authentication bypass in Jenkins
IDs: CVE-2020-2099, GHSA-qp4f-2w67-c8hw
Record: https://patchnext.com/advisories/cve-2020-2099 (revision 1, source checked 26 Oct 2026, 16:20 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: org.jenkins-ci.main:jenkins-core 2.214, 2.204.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Maven org.jenkins-ci.main:jenkins-core: affected < 2.204.2; >= 2.205, < 2.214; fixed in 2.204.2, 2.214

## Suggested inspection (read-only)
- Maven org.jenkins-ci.main:jenkins-core: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on org.jenkins-ci.main:jenkins-core.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-qp4f-2w67-c8hw (GitHub-reviewed advisory GHSA-qp4f-2w67-c8hw lists affected ranges: Maven org.jenkins-ci.main:jenkins-core >=0 =2.205 <2.214)

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