CVE-2026-21577 in Confluence Data Center
Summary
by MITRE • 07/21/2026
This High severity DoS (Denial of Service) vulnerability was introduced in versions 9.0.1, 9.1.0, 9.2.0, 9.3.1, 9.4.0, 9.5.1, 10.0.2, 10.1.0 and 10.2.0 of Confluence Data Center.
This DoS (Denial of Service) vulnerability, with a CVSS Score of 7.1, allows an authenticated attacker to cause a resource to be unavailable for its intended users by temporarily or indefinitely disrupting services of a host connected to a network.
Atlassian recommends that Confluence Data Center customers upgrade to latest version, if you are unable to do so, upgrade your instance to one of the specified supported fixed versions: Confluence Data Center 9.2: Upgrade to a release greater than or equal to 9.2.17
Confluence Data Center 10.2: Upgrade to a release greater than or equal to 10.2.7
See the release notes ([https://confluence.atlassian.com/doc/confluence-release-notes-327.html]). You can download the latest version of Confluence Data Center from the download center ([https://www.atlassian.com/software/confluence/download-archives]).
This vulnerability was reported via our Penetration Testing program.
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Analysis
by VulDB Data Team • 07/21/2026
This denial of service vulnerability affects Atlassian Confluence Data Center versions 9.0.1 through 10.2.0, representing a significant security concern with a CVSS score of 7.1 that falls into the high severity category. The flaw specifically targets authenticated attackers who can exploit this weakness to disrupt services by making system resources unavailable to legitimate users. This vulnerability operates as a resource exhaustion attack that can temporarily or indefinitely interrupt service availability for users connected to the network infrastructure hosting Confluence Data Center instances.
The technical nature of this vulnerability stems from improper handling of specific input patterns within the Confluence processing pipeline, creating conditions where authenticated users can manipulate system resources through crafted requests that trigger excessive memory consumption or thread blocking. This type of flaw typically aligns with CWE-400 vulnerability categories related to resource exhaustion and can be categorized under ATT&CK technique T1499.1 for network denial of service attacks. The vulnerability's impact extends beyond simple service interruption as it can potentially affect system stability, user productivity, and overall business operations when exploited successfully.
The operational implications of this vulnerability are substantial for organizations relying on Confluence Data Center for collaborative documentation and knowledge management. Attackers with valid authentication credentials can leverage this weakness to cause sustained disruptions that may require manual intervention to resolve, including system restarts or resource cleanup procedures. Organizations using affected versions face potential business continuity issues, as the denial of service can impact access to critical documentation systems, collaboration features, and enterprise knowledge repositories that depend on Confluence for their operation.
Mitigation strategies should prioritize immediate upgrading to patched versions as recommended by Atlassian, specifically targeting Confluence Data Center 9.2.17 or higher for version 9.2 installations, and 10.2.7 or higher for version 10.2 deployments. Organizations unable to perform immediate upgrades should implement network-level controls including rate limiting, access control lists, and monitoring solutions to detect anomalous patterns that may indicate exploitation attempts. The vulnerability's discovery through Atlassian's penetration testing program indicates it was identified through systematic security assessment rather than accidental discovery, emphasizing the importance of regular security evaluations and timely patch management processes. Organizations should also consider implementing additional logging and monitoring capabilities to detect potential exploitation attempts before they can cause significant service disruption.