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CVE-2026-21580 – Unauthenticated Stored XSS with Privilege Escalation – Atlassian Confluence Data Ce

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Summary

CVE-2026-21580 is a high-severity vulnerability in Atlassian Confluence Data Center and Server that combines a stored Cross-Site Scripting (XSS) flaw with a privilege escalation issue and a security misconfiguration weakness. It allows an unauthenticated attacker to inject arbitrary HTML or JavaScript that executes in a victim’s browser, potentially enabling actions to be performed as a higher-privileged user. The issue was reported through Atlassian’s Bug Bounty program and carries a CVSS score of 8.6 (High).

Technical details

  • Root cause: A combination of insufficient input sanitization (enabling stored XSS) and a security misconfiguration that exposes functionality otherwise protected by security best practices.
  • Trigger conditions: An unauthenticated attacker submits or persists malicious HTML/JavaScript content on a vulnerable Confluence instance; the payload later executes when a victim (potentially a higher-privileged user) views the affected page.
  • Attack vector: Network-based; no authentication is required to inject the payload (PR:N, UI:N per the CVSS vector), making the flaw exploitable against internet-exposed instances.
  • Impact: Successful exploitation can allow the attacker’s script to run in the browser context of another user, and combined with the privilege escalation component, to act with that user’s elevated privileges — potentially leading to full compromise of confidentiality, integrity, and availability of affected data.

Affected software

  • Confluence Data Center: 7.19.27–7.19.30, 8.5.15–8.5.31, 8.9.6–8.9.8, 9.0.3, 9.1.0–9.1.1, 9.2.0–9.2.20, 9.3.1–9.3.2, 9.4.0–9.4.1, 10.0.2–10.0.3, 10.1.0–10.1.2, 10.2.0–10.2.11
  • Confluence Server: 7.19.27–7.19.30, 8.5.15–8.5.31

Severity

CVSS v4.0 Base Score: 8.6 (High)
Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Mitigation and recommended actions

  • Immediate: Upgrade Confluence Data Center/Server to a fixed release — 9.2.21 or later (for the 9.2 line) or 10.2.13 or later (for the 10.2 line). Customers on other affected version lines should upgrade to the latest available fixed release for their line as published by Atlassian.
  • If immediate patching is not possible: Restrict network exposure of the Confluence instance (e.g., limit access to trusted internal networks or VPN), enforce strict content security policies where supported, and monitor for anomalous content submissions or privilege changes until the upgrade can be applied.

References

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