CVE-2026-21588 Overview
CVE-2026-21588 is a Denial of Service (DoS) vulnerability affecting Atlassian Confluence Data Center. An authenticated attacker can exploit this flaw over the network to make a resource unavailable to legitimate users by temporarily or indefinitely disrupting services on the affected host. The vulnerability was introduced across multiple release lines and reported through Atlassian's Penetration Testing program. It is categorized under [CWE-400] Uncontrolled Resource Consumption.
Critical Impact
An authenticated attacker with low privileges can disrupt availability of Confluence Data Center services over the network, impacting collaboration workflows and dependent business processes.
Affected Products
- Atlassian Confluence Data Center versions 8.9.0, 9.0.1, 9.1.0, 9.2.0, 9.3.1, 9.4.0, and 9.5.1
- Atlassian Confluence Data Center versions 10.0.2 and 10.1.0
- Atlassian Confluence Data Center version 10.2.0
Discovery Timeline
- 2026-09-15 - CVE-2026-21588 published to NVD
- 2026-09-16 - Last updated in NVD database
Technical Details for CVE-2026-21588
Vulnerability Analysis
CVE-2026-21588 is a Denial of Service condition in Confluence Data Center that an authenticated attacker can trigger over the network. Exploitation requires only low privileges and no user interaction, making it accessible to any user with a valid account on the target instance. Successful exploitation disrupts service availability without impacting confidentiality or integrity of stored data.
Atlassian identifies the weakness as Uncontrolled Resource Consumption [CWE-400]. This class of flaw occurs when the application fails to limit the allocation of a finite resource such as CPU, memory, threads, or file handles. Repeated or crafted requests exhaust the resource and prevent Confluence from serving legitimate users.
The issue affects multiple release lines simultaneously, indicating a code path present across several major versions. Atlassian has not published exploitation details, and no public proof-of-concept is available at this time.
Root Cause
The vulnerability stems from insufficient enforcement of resource limits within an authenticated Confluence Data Center code path. Atlassian tracks the fix internally as CONFSERVER-104451. Full technical details are restricted to preserve customer patching windows.
Attack Vector
The attack requires network access to the Confluence Data Center instance and a valid authenticated session with low privileges. The attacker sends requests that cause the server to consume excessive resources, degrading or halting service for other users. No user interaction is required, and the scope of impact is limited to availability of the affected host.
Because no verified proof-of-concept has been published, this article does not include exploitation code. Refer to the Atlassian Jira Issue CONFSERVER-104451 for vendor-tracked details.
Detection Methods for CVE-2026-21588
Indicators of Compromise
- Sudden spikes in CPU, memory, or thread utilization on Confluence Data Center nodes without corresponding legitimate user activity.
- Repeated requests from a single authenticated session immediately preceding service unresponsiveness or timeouts.
- Application logs showing thread pool exhaustion, out-of-memory errors, or database connection saturation.
Detection Strategies
- Correlate authenticated user sessions with resource utilization metrics to identify accounts generating disproportionate load.
- Baseline normal request rates per endpoint and alert on statistically significant deviations from low-privilege user accounts.
- Monitor the Confluence application server for repeated HTTP 5xx responses or unresponsive health checks that coincide with authenticated activity.
Monitoring Recommendations
- Enable verbose access logging on Confluence Data Center and forward logs to a centralized SIEM for correlation.
- Track JVM metrics including heap usage, garbage collection frequency, and active thread counts on all Confluence nodes.
- Alert on database connection pool saturation and long-running queries originating from Confluence application requests.
How to Mitigate CVE-2026-21588
Immediate Actions Required
- Inventory all Confluence Data Center deployments and identify instances running affected versions listed in the Atlassian advisory.
- Upgrade Confluence Data Center 9.2.x to a release greater than or equal to 9.2.24.
- Upgrade Confluence Data Center 10.2.x to a release greater than or equal to 10.2.17, or upgrade to the latest available version.
- Restrict network access to Confluence Data Center administrative interfaces to trusted networks where feasible.
Patch Information
Atlassian recommends upgrading to the latest version of Confluence Data Center. Fixed versions are 9.2.24 or later for the 9.2 line and 10.2.17 or later for the 10.2 line. Refer to the Atlassian Confluence Documentation and the Atlassian Jira Issue CONFSERVER-104451 for release details.
Workarounds
- Apply rate limiting at a reverse proxy or web application firewall in front of Confluence to constrain request volume per authenticated user.
- Enforce strong authentication controls and disable inactive accounts to reduce the population of users who could trigger the vulnerability.
- Monitor and cap resource utilization at the JVM and operating system level to contain the impact of exhaustion attempts until patching is complete.
# Configuration example
# Refer to vendor documentation for authoritative upgrade steps.
# Example: verify Confluence version prior to upgrade
grep -i 'confluence.version' /opt/atlassian/confluence/confluence/META-INF/maven/com.atlassian.confluence/confluence-webapp/pom.properties
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
