Jenkins vulnerable to UDP amplification reflection attack

Exploitation

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

CVSS

5.8 · CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:L

EPSS

• CVE-2020-2100: 3.44% estimated exploitation activity in the next 30 days; percentile 89.01 (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 2.218 and earlier, LTS 2.204.1 and earlier supports two network discovery services (UDP multicast/broadcast and DNS multicast) by default. The UDP multicast/broadcast service can be used in an amplification reflection attack, as very few bytes sent to the respective endpoint result in much larger responses: A single byte request to this service would respond with more than 100 bytes of Jenkins metadata which could be used in a DDoS attack on a Jenkins controller. Within the same network, spoofed UDP packets could also be sent to make two Jenkins controllers go into an infinite loop of replies to one another, thus causing a denial of service. Jenkins 2.219, LTS 2.204.2 now disables both UDP multicast/broadcast and DNS multicast by default. Administrators that need these features can re-enable them again by setting the system property hudson.DNSMultiCast.disabled to false (for DNS multicast) or the system property hudson.udp to 33848, or another port (for UDP…

Published by the source

24 May 2022, 17:07 UTC

Last modified by the source

22 Dec 2023, 13:57 UTC

Source last checked

26 Oct 2026, 16:24 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-gpxv-776p-7gc7

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# Patch Next advisory brief: CVE-2020-2100

Advisory: Jenkins vulnerable to UDP amplification reflection attack
IDs: CVE-2020-2100, GHSA-gpxv-776p-7gc7
Record: https://patchnext.com/advisories/cve-2020-2100 (revision 1, source checked 26 Oct 2026, 16:24 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Medium (CVSS 5.8)
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 2.219, 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, < 2.219; fixed in 2.204.2, 2.219

## 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-gpxv-776p-7gc7 (GitHub-reviewed advisory GHSA-gpxv-776p-7gc7 lists affected ranges: Maven org.jenkins-ci.main:jenkins-core >=0 =2.205 <2.219)

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