CVE-2026-21577: Confluence Data Center DoS Vulnerability

CVE-2026-21577 Overview

CVE-2026-21577 is a high severity Denial of Service (DoS) vulnerability affecting Atlassian Confluence Data Center. The flaw allows an authenticated attacker to make a resource unavailable to legitimate users by disrupting services on the host. Atlassian discovered the issue through its Penetration Testing program. The vulnerability is classified under CWE-400 (Uncontrolled Resource Consumption). Affected releases include 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.

Critical Impact
An authenticated attacker can temporarily or indefinitely disrupt Confluence Data Center services, impacting availability for all users of the platform.

Affected Products

Atlassian Confluence Data Center 9.0.1, 9.1.0, 9.2.0, 9.3.1, 9.4.0, 9.5.1
Atlassian Confluence Data Center 10.0.2, 10.1.0
Atlassian Confluence Data Center 10.2.0

Discovery Timeline

2026-07-21 - CVE-2026-21577 published to NVD
2026-07-22 - Last updated in NVD database

Technical Details for CVE-2026-21577

Vulnerability Analysis

The vulnerability enables an authenticated user to trigger uncontrolled resource consumption within Confluence Data Center. Exploitation targets service availability rather than confidentiality or integrity. The attack is remotely reachable over the network and requires low privileges with no user interaction. Successful exploitation can render Confluence unavailable to legitimate users, blocking collaboration and knowledge base access across an enterprise.

Atlassian classifies the issue under CWE-400, which covers scenarios where an application fails to properly limit the allocation or consumption of a finite resource. The EPSS probability is currently 0.235% (percentile 14.4), reflecting a low observed likelihood of near-term exploitation.

Root Cause

The root cause is uncontrolled resource consumption in Confluence Data Center request handling. The affected code paths do not adequately constrain the CPU, memory, or thread resources consumed when processing specific requests from authenticated users. Repeated or crafted requests can drive resource exhaustion until the service becomes unresponsive.

Attack Vector

Exploitation requires an authenticated Confluence account and network reachability to the Confluence Data Center instance. The attacker sends requests that trigger the resource-exhausting code paths. No user interaction is required. Because Confluence Data Center is often deployed for internal collaboration, insider accounts and compromised low-privilege credentials are the primary threat vectors.

No public proof-of-concept exploit is available at this time. Technical details are limited to the Atlassian advisory and JIRA issue CONFSERVER-104334.

Detection Methods for CVE-2026-21577

Indicators of Compromise

Sudden spikes in CPU, memory, or thread utilization on Confluence Data Center nodes without corresponding legitimate traffic patterns.
Repeated requests to the same Confluence endpoint from a single authenticated user session over a short interval.
Elevated response latency or HTTP 5xx errors across Confluence services correlating with a specific user account.

Detection Strategies

Baseline normal Confluence request rates per authenticated user and alert on statistical outliers.
Correlate application server resource metrics with access logs to identify user accounts that precede resource spikes.
Review Confluence access logs for authenticated sessions that generate abnormally high request volumes to expensive endpoints.

Monitoring Recommendations

Ingest Confluence access logs, application logs, and JVM metrics into a centralized SIEM for correlation.
Monitor Tomcat/JVM thread pool saturation and garbage collection pauses on Confluence nodes.
Configure alerts for sustained CPU utilization above defined thresholds on Confluence Data Center hosts.

How to Mitigate CVE-2026-21577

Immediate Actions Required

Identify all Confluence Data Center instances running affected versions and prioritize them for patching.
Restrict Confluence Data Center network exposure so only authorized users on trusted networks can authenticate.
Review Confluence user accounts and disable or rotate credentials for inactive or unnecessary accounts.
Enable rate limiting on the reverse proxy or web application firewall in front of Confluence.

Patch Information

Atlassian recommends upgrading Confluence Data Center to the latest available release. Customers who cannot move to the latest version should upgrade to a fixed maintenance release: Confluence Data Center 9.2 users should upgrade to 9.2.17 or later, and Confluence Data Center 10.2 users should upgrade to 10.2.7 or later. Refer to the Confluence release notes and download fixed versions from the Atlassian download archives.

Workarounds

Apply strict rate limits at the reverse proxy or load balancer to constrain requests per authenticated session.
Enforce least privilege on Confluence accounts and remove unnecessary users to reduce the authenticated attack surface.
Place Confluence Data Center behind a VPN or zero-trust network access solution to limit exposure to trusted users.
Monitor JVM heap and thread usage and configure automatic restart policies to recover from resource exhaustion conditions.

bash

# Example NGINX rate limiting for Confluence Data Center
http {
    limit_req_zone $binary_remote_addr zone=confluence_limit:10m rate=30r/m;

    server {
        location / {
            limit_req zone=confluence_limit burst=20 nodelay;
            proxy_pass http://confluence_backend;
        }
    }
}