CVE-2021-21610Network attack vector

Reflected XSS via unrestricted markup preview URL

Published Jan 13, 2021 · Updated Aug 3, 2024

Reflected XSS in Jenkins 2.274 and earlier and LTS 2.263.1 and earlier allows remote attackers to execute JavaScript via a crafted preview URL. The markup preview URL renders query-parameter markup without method restrictions or a restrictive Content Security Policy. Exploitation requires a configured formatter that permits JavaScript and user interaction with the crafted URL; the script runs in the user's Jenkins origin.

CVSS severity6.1
Medium
EPSS probability1.19%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Reflected XSS in Jenkins 2.274 and earlier and LTS 2.263.1 and earlier allows remote attackers to execute JavaScript via a crafted preview URL. The markup preview URL renders query-parameter markup without method restrictions or a restrictive Content Security Policy. Exploitation requires a configured formatter that permits JavaScript and user interaction with the crafted URL; the script runs in the user's Jenkins origin.

The record

CVE
CVE-2021-21610
Published
Jan 13, 2021
Updated
Aug 3, 2024
Vendor
Jenkins Project
Product
Jenkins
Classifications
CWE-79, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jan 13, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <=2.274
  2. Affected versionversion=unspecified <=LTS 2.263.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Jenkins Project · Jenkinsversion=unspecified <=2.274; version=unspecified <=LTS 2.263.1

Published CVSS scores

6.1NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
4.3NVDAV:N/AC:M/Au:N/C:N/I:P/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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