CVE-2025-6016: GitLab Denial of Service Vulnerability

CVE-2025-6016 Overview

CVE-2025-6016 is a Resource Exhaustion vulnerability affecting GitLab Community Edition (CE) and Enterprise Edition (EE). The vulnerability exists due to insufficient resource allocation limits when retrieving notes under certain conditions, allowing an authenticated user to cause a denial of service condition. This vulnerability impacts all GitLab versions from 9.2 through 18.9.5, 18.10 through 18.10.3, and version 18.11.0.

Critical Impact

Authenticated attackers can exhaust server resources by exploiting the notes retrieval functionality, potentially causing service disruption for all GitLab users on the affected instance.

Affected Products

• GitLab Community Edition (CE) versions 9.2 to 18.9.5
• GitLab Enterprise Edition (EE) versions 9.2 to 18.9.5
• GitLab CE/EE versions 18.10 to 18.10.3
• GitLab CE/EE version 18.11.0

Discovery Timeline

• 2026-04-22 - CVE-2025-6016 published to NVD
• 2026-04-22 - GitLab releases security patch (versions 18.11.1, 18.10.4, 18.9.6)
• 2026-04-23 - Last updated in NVD database

Technical Details for CVE-2025-6016

Vulnerability Analysis

This vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling). The core issue stems from the notes retrieval functionality in GitLab failing to properly limit the resources allocated during processing. When an authenticated user requests notes under specific conditions, the application does not enforce adequate bounds on resource consumption, allowing an attacker to trigger excessive memory or CPU usage.

The network-accessible nature of this vulnerability means that any authenticated user with access to a GitLab instance can potentially exploit it remotely. While the attack requires valid authentication credentials, the low complexity of exploitation makes it relatively straightforward for malicious insiders or compromised accounts to trigger the denial of service.

The impact is primarily on availability, with no direct effect on data confidentiality or integrity. However, a successful attack could render the GitLab instance unavailable to all users, disrupting development workflows, CI/CD pipelines, and collaboration activities.

Root Cause

The root cause is insufficient resource allocation limits (CWE-770) in the notes retrieval component. GitLab failed to implement proper throttling or boundaries when processing note retrieval requests, allowing unbounded resource consumption. This type of vulnerability typically occurs when input size or quantity is not validated against reasonable limits, or when recursive or iterative operations lack termination controls based on resource consumption.

Attack Vector

The attack can be executed over the network by any authenticated user. The attacker exploits the notes retrieval functionality by crafting requests that trigger excessive resource allocation. Given that this is a resource exhaustion attack, the exploitation involves making requests under conditions that maximize resource consumption without proper rate limiting or quota enforcement.

An authenticated attacker could:

1. Authenticate to the GitLab instance using valid credentials
2. Identify the vulnerable notes retrieval endpoint or functionality
3. Submit requests designed to trigger maximum resource consumption
4. Repeat requests to exhaust server resources and cause denial of service

The vulnerability was reported through GitLab's HackerOne bug bounty program, as documented in HackerOne Report #3160363.

Detection Methods for CVE-2025-6016

Indicators of Compromise

• Unusual spikes in memory or CPU usage on GitLab servers during notes retrieval operations
• Increased response times or timeouts when accessing GitLab functionality
• Application logs showing excessive note retrieval requests from specific authenticated users
• Server resource exhaustion alerts correlating with authenticated user activity

Detection Strategies

• Monitor GitLab application logs for anomalous patterns in notes-related API requests
• Implement alerting on server resource utilization thresholds (CPU, memory, connections)
• Track per-user request rates to the notes retrieval functionality for unusual volumes
• Deploy application performance monitoring to detect degradation patterns associated with this attack vector

Monitoring Recommendations

• Enable detailed logging for GitLab API endpoints, particularly those related to notes and comments
• Configure infrastructure monitoring to alert on sudden resource consumption spikes
• Implement rate limiting visibility to identify users exceeding expected request patterns
• Review GitLab Rails logs for errors or warnings related to resource allocation

How to Mitigate CVE-2025-6016

Immediate Actions Required

• Upgrade GitLab CE/EE to version 18.11.1, 18.10.4, or 18.9.6 immediately
• Review recent authentication logs to identify any potential exploitation attempts
• Consider implementing additional rate limiting at the network/proxy level as a temporary measure
• Monitor server resources closely until patching is complete

Patch Information

GitLab has released patched versions addressing this vulnerability. Organizations should upgrade to the following versions:

• GitLab 18.11.1 - For organizations running the 18.11.x branch
• GitLab 18.10.4 - For organizations running the 18.10.x branch
• GitLab 18.9.6 - For organizations running versions 9.2 through 18.9.x

The official patch release announcement is available at the GitLab Patch Release 18.11.1 page. Technical details about the fix can be found in GitLab Work Item #548940.

Workarounds

• Implement network-level rate limiting for authenticated GitLab API requests
• Configure reverse proxy (nginx, Apache) to limit request rates per authenticated session
• Restrict access to GitLab instances to trusted networks where possible
• Monitor and alert on abnormal resource consumption patterns to enable rapid response

# Example nginx rate limiting configuration for GitLab
# Add to nginx configuration for GitLab
limit_req_zone $binary_remote_addr zone=gitlab_notes:10m rate=10r/s;

# Apply to GitLab location block
location / {
    limit_req zone=gitlab_notes burst=20 nodelay;
    proxy_pass http://gitlab-workhorse;
}