CVE-2020-2100 is a medium-severity (CVSS 5.8) 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.
Jenkins vulnerable to UDP amplification reflection attack
EPSS Exploitation Probability
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
org.jenkins-ci.main:jenkins-core☕org.jenkins-ci.main:jenkins-coreReal-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 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 broadcast/multicast). These are the same system properties that controlled whether these features were enabled in the past, so any instances explicitly enabling these features by setting these system properties will continue to have them enabled.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| ☕Maven | org.jenkins-ci.main:jenkins-core | all versions | 2.204.2org.jenkins-ci.main:jenkins-core:2.204.2 |
| ☕Maven | org.jenkins-ci.main:jenkins-core | ≥ 2.205&&< 2.219 | 2.219org.jenkins-ci.main:jenkins-core:2.219 |
Affected Products
jenkinsjenkinsDetection & mitigation playbook
Open-source dependencyDetect
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.
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 CVE-2020-2100 is resolved across your whole dependency graph.
Workarounds
Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.
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.
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat OpenShift Container Platform 3.11 | atomic-enterprise-service-catalog-1:3.11.170-1.git.1.91db82e.el7 | RHBA-2020:0402 |
| Red Hat OpenShift Container Platform 4.3 | jenkins-0:2.204.2.1583446818-1.el7 | RHBA-2020:0675 |
| Red Hat OpenShift Container Platform 4.4 | openshift4/ose-aws-machine-controllers:v4.4.0-202004261927 | RHBA-2020:0581 |
| Red Hat OpenShift Container Platform 4.5 | openshift4/ose-aws-machine-controllers:v4.5.0-202007012112.p0 | RHBA-2020:2409 |
Frequently Asked Questions
Is CVE-2020-2100 in your dependencies?
Find it across Maven, including transitive dependencies.