CVE-2025-13927: GitLab CE/EE DoS Vulnerability

CVE-2025-13927 Overview

CVE-2025-13927 is a Denial of Service vulnerability affecting GitLab Community Edition (CE) and Enterprise Edition (EE) that allows an unauthenticated attacker to disrupt service availability by sending crafted requests containing malformed authentication data. This vulnerability affects all GitLab versions from 11.9 through multiple release branches, representing a significant attack surface for organizations running unpatched GitLab instances.

The vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling), indicating that the authentication parsing mechanism fails to properly limit resource consumption when processing malicious input.

Critical Impact

Unauthenticated attackers can cause denial of service conditions on GitLab instances, potentially disrupting critical development and CI/CD workflows for entire organizations without requiring any credentials.

Affected Products

• GitLab CE/EE versions 11.9 to 18.6.3 (fixed in 18.6.4)
• GitLab CE/EE versions 18.7 to 18.7.1 (fixed in 18.7.2)
• GitLab CE/EE versions 18.8 to 18.8.1 (fixed in 18.8.2)

Discovery Timeline

• 2026-01-21 - GitLab releases security patch in version 18.8.2
• 2026-01-22 - CVE-2025-13927 published to NVD
• 2026-01-22 - Last updated in NVD database

Technical Details for CVE-2025-13927

Vulnerability Analysis

This vulnerability stems from improper resource allocation handling when GitLab processes authentication requests containing malformed data. The flaw allows unauthenticated remote attackers to exhaust server resources by sending specially crafted HTTP requests that exploit weaknesses in the authentication parsing logic.

The network-accessible nature of this vulnerability means any GitLab instance exposed to the network can be targeted. No user interaction or authentication is required to exploit this flaw, making it particularly dangerous for public-facing GitLab deployments. The impact is limited to availability—there is no compromise of confidentiality or integrity—but the disruption to development operations can be severe.

Organizations running affected GitLab versions face the risk of complete service unavailability if targeted by this attack, potentially halting code commits, merge requests, CI/CD pipelines, and collaborative development activities.

Root Cause

The root cause is classified as CWE-770: Allocation of Resources Without Limits or Throttling. The authentication processing component in GitLab fails to implement proper bounds checking or rate limiting when parsing authentication data structures. When malformed authentication payloads are received, the system attempts to process them without adequate safeguards, leading to excessive resource consumption.

This type of vulnerability typically occurs when input validation assumes well-formed data or when resource allocation is proportional to attacker-controlled input without upper bounds.

Attack Vector

The attack vector is network-based, requiring no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Identifying a target GitLab instance accessible over the network
2. Crafting HTTP requests with malformed authentication data in request headers or body
3. Sending a volume of these crafted requests to overwhelm server resources
4. Causing legitimate users to experience service degradation or complete unavailability

The vulnerability was reported through GitLab's HackerOne bug bounty program, as documented in HackerOne Report #3439683. Technical details and vendor discussion can be found in GitLab Issue #582737.

Detection Methods for CVE-2025-13927

Indicators of Compromise

• Unusual volume of authentication-related HTTP requests from single or limited IP addresses
• Server resource exhaustion (CPU, memory, or connection pool depletion) coinciding with authentication traffic patterns
• Application logs showing repeated malformed authentication attempts or parsing errors
• Increased latency or timeout errors reported by legitimate GitLab users

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block requests with abnormally large or malformed authentication headers
• Monitor GitLab application logs for authentication parsing errors or exceptions that may indicate exploitation attempts
• Configure network intrusion detection systems (IDS) to alert on high-frequency request patterns targeting authentication endpoints
• Deploy behavioral analysis to identify deviations from baseline authentication traffic patterns

Monitoring Recommendations

• Enable detailed logging for GitLab authentication subsystems to capture request metadata
• Set up alerting thresholds for server resource utilization metrics (CPU, memory, active connections)
• Monitor GitLab-specific health endpoints for service degradation indicators
• Implement real-time dashboards to visualize authentication request rates and error patterns

How to Mitigate CVE-2025-13927

Immediate Actions Required

• Upgrade GitLab CE/EE to version 18.8.2, 18.7.2, or 18.6.4 immediately depending on your release branch
• If immediate patching is not possible, implement network-level rate limiting on authentication endpoints
• Review firewall rules to restrict GitLab access to trusted networks where feasible
• Enable enhanced logging to detect potential exploitation attempts during the upgrade window

Patch Information

GitLab has released patched versions addressing this vulnerability. Organizations should upgrade to the following versions based on their current release branch:

The official patch release announcement is available in the GitLab Patch Release 18.8.2 documentation. Organizations are strongly encouraged to follow GitLab's standard upgrade procedures and test in staging environments before production deployment.

Workarounds

• Deploy a reverse proxy or WAF to filter requests with malformed or oversized authentication data before they reach GitLab
• Implement IP-based rate limiting at the network perimeter for requests to authentication endpoints
• Temporarily restrict GitLab access to VPN or internal networks if the instance does not require public accessibility
• Configure connection limits on load balancers to prevent resource exhaustion from reaching backend GitLab servers

# Example nginx rate limiting configuration for GitLab authentication endpoints
limit_req_zone $binary_remote_addr zone=gitlab_auth:10m rate=10r/s;

server {
    location ~ ^/(users/sign_in|oauth/token|api/v4/session) {
        limit_req zone=gitlab_auth burst=20 nodelay;
        limit_req_status 429;
        proxy_pass http://gitlab_backend;
    }
}