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CVE-2026-27099 is a stored cross-site scripting vulnerability in Jenkins Core affecting Jenkins 2.483 through 2.550 inclusive and Jenkins LTS 2.492.1 through 2.541.1 inclusive. The flaw is in the handling of the user-supplied description for the "Mark temporarily offline" offline cause on Jenkins agents/nodes. Since Jenkins 2.483, offline cause descriptions allowed HTML content, but in affected versions that input was not properly escaped before being rendered. An attacker with Agent/Configure or Agent/Disconnect permission can store crafted HTML/JavaScript in the offline cause description, causing script execution in the browsers of other users who view the affected Jenkins UI.
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No public exploit code observed for this vulnerability.
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A stored XSS vulnerability in Jenkins' 'Mark temporarily offline' field that can enable session hijacking for users with agent configure permissions.
A high-severity stored cross-site scripting vulnerability in Jenkins Core where user-controlled “node offline cause description” HTML is not properly escaped, enabling JavaScript injection and potential session compromise of other users.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.