CVE-2026-21588 in Confluence Data Center
Summary
by MITRE • 09/15/2026
This High severity DoS (Denial of Service) vulnerability was introduced in versions 8.9.0, 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 9.2.24
Confluence Data Center 10.2: Upgrade to a release greater than or equal to 10.2.17
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.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 09/15/2026
A high severity Denial of Service vulnerability has been identified within Atlassian Confluence Data Center, affecting multiple versions including 8.9.0 through 10.2.0. This flaw carries a CVSS score of 7.1 and is classified as critical due to its potential to disrupt business operations by rendering the service unavailable to legitimate users. The vulnerability allows an authenticated attacker to trigger conditions that cause significant resource exhaustion or processing loops, effectively halting normal functionality for all connected clients. Because authentication is required, this represents a threat from insider actors or compromised user accounts rather than unauthenticated external attackers, yet the impact remains severe given the central role Confluence plays in many enterprise knowledge management workflows.
The technical nature of this vulnerability aligns with CWE-400, which describes Uncontrolled Resource Consumption leading to Denial of Service conditions. When triggered, the flaw likely causes excessive memory allocation, CPU saturation, or thread blocking within the application server layers that support Confluence Data Center clusters. This results in a temporary or indefinite disruption of services for hosts connected to the network. The operational impact is substantial as it prevents authorized personnel from accessing documentation, collaborating on projects, and retrieving critical information stored within the platform. In a data center environment where high availability is paramount, such disruptions can lead to significant productivity losses and potential SLA violations depending on the duration of the outage.
From an offensive security perspective, this vulnerability maps to MITRE ATT&CK technique T1499, Endpoint Denial of Service, specifically under sub-techniques involving resource exhaustion or service disruption. The fact that it was reported via a penetration testing program indicates that the attack vector is exploitable through standard application interactions once valid credentials are obtained. This highlights the importance of strict access controls and monitoring for anomalous behavior from authenticated users who may attempt to abuse system resources. Attackers with legitimate but potentially compromised accounts can leverage this flaw as part of a broader campaign to degrade service availability, thereby creating chaos that might mask other malicious activities or simply serve as an act of sabotage.
Atlassian has acknowledged the severity of this issue and recommends immediate remediation by upgrading Confluence Data Center to one of the specified fixed versions. For customers running version 9.2.x, it is necessary to upgrade to a release greater than or equal to 9.2.24. Similarly, those on the 10.2 branch must upgrade to at least version 10.2.17. These updates contain code changes that address the underlying logic flaw responsible for the resource exhaustion. Organizations unable to perform an immediate full upgrade should consider applying these specific patch levels as a priority mitigation strategy. The release notes and download archives provided by Atlassian serve as the authoritative sources for obtaining these corrected binaries, ensuring that the deployed instances are resilient against this specific denial of service attack vector.
To further mitigate risk while planning upgrades, organizations should implement network-level controls such as rate limiting on API endpoints and application traffic to prevent any single user or session from overwhelming system resources. Additionally, enforcing multi-factor authentication and reviewing account permissions can reduce the likelihood that an attacker gains the necessary authenticated access to exploit this flaw. Continuous monitoring of server metrics for unusual spikes in CPU or memory usage associated with specific Confluence sessions can also aid in early detection of exploitation attempts. By combining timely software updates with robust operational security practices, enterprises can effectively neutralize the threat posed by this vulnerability and maintain the integrity and availability of their collaboration platforms.