CVE-2020-2100: Medium severity Jenkins Jenkins vulnerability
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.
Other sources
Jenkins 2.218 and earlier, LTS 2.204.1 and earlier was vulnerable to a UDP amplification reflection denial of service attack on port 33848.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
maven/org.jenkins-ci.main:jenkins-coreto a version that resolves this vulnerability.Fixed in 2.219 - Upgrade
Upgrade
maven/org.jenkins-ci.main:jenkins-coreto a version that resolves this vulnerability.Fixed in 2.204.2 - Upgrade
Upgrade
jenkinsto a version that resolves this vulnerability.Fixed in 2.219 - Upgrade
Upgrade
jenkinsto a version that resolves this vulnerability.Fixed in 2.204.2 - Configuration
Ensure DNS multicast discovery is disabled by setting the system property hudson.DNSMultiCast.disabled to true (Jenkins 2.219 / LTS 2.204.2 disables DNS multicast by default).
Jenkins hudson.DNSMultiCast.disabled = true - Configuration
Ensure UDP broadcast/multicast discovery is disabled by setting the system property hudson.udp to 33848 (or another port) as shown in the text for UDP broadcast/multicast; avoid explicitly enabling UDP multicast/broadcast on the vulnerable discovery endpoint (Jenkins 2.219 / LTS 2.204.2 disables UDP multicast/broadcast by default).
Jenkins hudson.udp = 33848
Event History
Frequently Asked Questions
What is the severity of CVE-2020-2100?
CVE-2020-2100 has a medium severity rating due to its potential for abuse in amplification reflection attacks.
How do I fix CVE-2020-2100?
To mitigate CVE-2020-2100, upgrade Jenkins to version 2.219 or later, or to 2.204.2 if using an LTS version.
What are the affected versions for CVE-2020-2100?
CVE-2020-2100 affects Jenkins versions 2.218 and earlier, including LTS versions up to 2.204.1.
What types of attacks are associated with CVE-2020-2100?
CVE-2020-2100 is associated with amplification reflection attacks that exploit its UDP multicast/broadcast service.
Does CVE-2020-2100 affect all Jenkins instances?
CVE-2020-2100 affects Jenkins instances running versions 2.218 and earlier by default, particularly those using enabled network discovery services.