How severe is CVE-2021-21635?

CVE-2021-21635 has a CVSS score of 5.4/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2021-21635?

CVE-2021-21635 affects the following packages: io.jenkins.plugins:rest-list-parameter (Maven). Ecosystems affected: Maven.

How do I fix CVE-2021-21635?

Update io.jenkins.plugins:rest-list-parameter to 1.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21635 is resolved across your whole dependency graph.

How do I detect CVE-2021-21635 in my Maven dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.jenkins.plugins:rest-list-parameter, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-21635 if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is CVE-2021-21635 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-21635 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-21635?

CVE-2021-21635 has an EPSS (Exploit Prediction Scoring System) score of 8.8%, placing it in the 95th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-21635?

CVE-2021-21635 is classified as Cross-site Scripting (XSS) (CWE-79). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2021-21635 published, and has it been updated?

CVE-2021-21635 was published on March 30, 2021 and was last updated on October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

☕

☕ Maven

Not in CISA KEV

MEDIUM severity

CVE-2021-21635 — rest-list-parameter

MEDIUMFix: jenkinsci/rest-list-parameter-plugin@ff4bb2b

CVE-2021-21635 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in io.jenkins.plugins:rest-list-parameter. A fix is available for io.jenkins.plugins:rest-list-parameter — see the affected versions and patch details below.

Stored XSS vulnerability in Jenkins REST List Parameter Plugin

Also known asGHSA-x3m6-vcp7-98mr

Published

Mar 30, 2021

Updated

Oct 24, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

8.8%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs95th percentile — riskier than 95% of all scored CVEsHighest risk

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

1 pkg affected

☕io.jenkins.plugins:rest-list-parameter

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 REST List Parameter Plugin 1.3.0 and earlier does not escape a parameter name reference in embedded JavaScript.

This results in a stored cross-site scripting (XSS) vulnerability exploitable by attackers with Job/Configure permission.

Jenkins REST List Parameter Plugin 1.3.1 no longer identifies a parameter using user-specified content.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
☕Maven	`io.jenkins.plugins:rest-list-parameter`	all versions	1.3.1`io.jenkins.plugins:rest-list-parameter:1.3.1`

Affected Products

1 product · 1 configurations

Application

rest list parameterjenkins

≤ 1.3.0

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for io.jenkins.plugins:rest-list-parameter, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update io.jenkins.plugins:rest-list-parameter to 1.3.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-21635 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

Jenkins REST List Parameter Plugin 1.3.0 and earlier does not escape a parameter name reference in embedded JavaScript. This results in a stored cross-site scripting (XSS) vulnerability exploitable by attackers with Job/Configure permission. Jenkins REST List Parameter Plugin 1.3.1 no longer identifies a parameter using user-specified content.

O3 Security · Impact-Aware SCA

Is CVE-2021-21635 in your dependencies?

Find it across Maven, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

5.4/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

Low

User Interaction

Required

Scope

Changed

Confidentiality

Low

Integrity

Low

Availability

None

Raw vector

CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

CWE Classification

CWE-79Cross-site Scripting (XSS)

Weaponization

No Nuclei template, Metasploit module or public proof-of-concept found.

Timeline

Disclosed

Mar 30, 2021

Last updated

Oct 24, 2026

Identifiers

CVE-2021-21635

GHSA-x3m6-vcp7-98mr

References

Advisoryopenwall.com Advisoryjenkins.io · 2021 03 30 Advisorynvd.nist.gov · CVE 2021 21635 Webgithub.com · ff4bb2b44eb05b35bfb68a3a63ac7c5e72cb96b6 Packagegithub.com · rest list parameter plugin

Related vulnerabilities

Also affects rest-list-parameter

This CVE is medium severity; 1 of 1 other CVE affecting rest-list-parameter is rated as high or higher (top: high).

CVE-2022-34196

Same weakness: CWE-79

This CVE is medium severity; 5 of 7 other CVEs with CWE-79 are rated as high or higher (top: high).

CVE-2026-126075CVE-2026-126063CVE-2026-110802CVE-2026-123364CVE-2026-118670CVE-2026-88986CVE-2026-63197Browse all CWE-79

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedOct 24, 2026