CVE-2021-21691Network attack vector

Controller file access via unchecked symlink creation

Published Nov 4, 2021 · Updated Aug 3, 2024

Authorization bypass in Jenkins 2.318 and earlier and LTS 2.303.2 and earlier allows attackers to create controller-side symbolic links. The agent-to-controller FilePath filter performs symbolic-link creation without checking the dedicated symlink permission. Exploitation requires control of an agent process and can expose controller files to read or write operations through crafted links.

CVSS severity9.8
Critical
EPSS probability2.10%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authorization bypass in Jenkins 2.318 and earlier and LTS 2.303.2 and earlier allows attackers to create controller-side symbolic links. The agent-to-controller FilePath filter performs symbolic-link creation without checking the dedicated symlink permission. Exploitation requires control of an agent process and can expose controller files to read or write operations through crafted links.

The record

CVE
CVE-2021-21691
Published
Nov 4, 2021
Updated
Aug 3, 2024
Vendor
Jenkins Project
Product
Jenkins
Classifications
CWE-59, T1005
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Nov 4, 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 <=2.318
  2. Affected versionversion=unspecified <=LTS 2.303.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Jenkins Project · Jenkinsversion=unspecified <=2.318; version=unspecified <=LTS 2.303.2

Published CVSS scores

9.8NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
9.0GitHub Advisory DatabaseCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:H
7.5NIST NVDAV:N/AC:L/Au:N/C:P/I:P/A:P

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 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-59Improper Link Resolution Before File Access ('Link Following')
T1005Data from Local System

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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