Known exploited · Atlassian

CVE-2021-26086: Atlassian Jira Server and Data Center Path Traversal Vulnerability

What it is

Atlassian Jira Server and Data Center contain a path traversal vulnerability that allows a remote attacker to read particular files in the /WEB-INF/web.xml endpoint.

Added November 12, 2024Due December 3, 2024CISA KEV catalog 2026.10.01

Vendor: Atlassian
Product: Jira Server and Data Center
Added to KEV: November 12, 2024
CISA due date: December 3, 2024
Ransomware use: Unknown
Weakness: CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

What CISA requires

Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.

Forensic triage

What to do now

Find every instance of Jira Server and Data Center you run, including the forgotten ones, and check its version against the vendor advisory.
Apply the vendor's fix or mitigation, before December 3, 2024 if you are bound by CISA's deadline, sooner if it faces the internet.
Assume it was tried against you already: look for signs of exploitation from the date it was added, not from the day you patched.
Until every instance is patched, block the attack at the edge: a WAF in blocking mode stops path traversal attempts.

References

CVE-2021-26086 in the National Vulnerability Database

The Dome

Block it at the edge while you patch

The Dome's WAF runs the OWASP Core Rule Set in blocking mode and stops path traversal attempts before they reach your application.

See the Dome

T Academy

Train the engineers who fix it

Security engineering on real hosts in the browser, every objective checked on the machine. The first two lessons of Linux 1 are free.

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Source: CISA Known Exploited Vulnerabilities Catalog (public domain), catalog version 2026.10.01.