CVE-2026-1102: GitLab CE/EE DoS Vulnerability

CVE-2026-1102 Overview

A denial of service vulnerability has been identified in GitLab CE/EE that allows unauthenticated attackers to disrupt service availability through malformed SSH authentication requests. This vulnerability affects a wide range of GitLab versions and poses a significant risk to organizations relying on GitLab for their development workflows.

The vulnerability enables remote attackers to send repeated malformed SSH authentication requests to GitLab instances, causing resource exhaustion and potential service disruption without requiring any authentication.

Critical Impact

Unauthenticated attackers can cause denial of service conditions on GitLab instances by sending malformed SSH authentication requests, potentially disrupting development operations and CI/CD pipelines.

Affected Products

• GitLab CE/EE versions 12.3 through 18.6.3
• GitLab CE/EE versions 18.7.0 through 18.7.1
• GitLab CE/EE versions 18.8.0 through 18.8.1

Discovery Timeline

• 2026-01-21 - GitLab releases security patch (versions 18.6.4, 18.7.2, and 18.8.2)
• 2026-01-22 - CVE CVE-2026-1102 published to NVD
• 2026-01-22 - Last updated in NVD database

Technical Details for CVE-2026-1102

Vulnerability Analysis

This vulnerability is classified under CWE-770 (Allocation of Resources Without Limits or Throttling). The flaw exists in GitLab's SSH authentication handling mechanism, which fails to properly limit or throttle incoming authentication requests.

When processing SSH authentication requests, GitLab does not adequately validate the format or implement sufficient rate limiting for malformed requests. This allows an attacker to consume server resources by flooding the SSH authentication endpoint with specially crafted requests, ultimately degrading service performance or causing complete unavailability.

The network-accessible nature of this vulnerability makes it particularly concerning, as attackers can launch attacks remotely without any prior authentication or special access to the target system.

Root Cause

The root cause of this vulnerability lies in insufficient resource allocation controls within GitLab's SSH authentication subsystem. Specifically, the system lacks proper validation and throttling mechanisms for incoming SSH authentication requests, allowing malformed requests to consume system resources without adequate bounds checking.

This represents a classic resource exhaustion scenario where the application fails to implement defensive measures against high-volume or malicious request patterns.

Attack Vector

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

1. Identifying a GitLab instance with SSH access enabled
2. Sending repeated malformed SSH authentication requests to the target
3. Overwhelming the authentication subsystem's ability to process requests
4. Causing degraded performance or complete denial of service

The attack does not require valid credentials or any special knowledge of the target system beyond network accessibility to the SSH service.

Detection Methods for CVE-2026-1102

Indicators of Compromise

• Unusual spikes in SSH authentication failures in GitLab logs
• High volume of connection attempts from single or multiple IP addresses to the SSH service
• Increased memory or CPU utilization on GitLab servers without corresponding legitimate activity
• SSH service becoming unresponsive or experiencing significant latency

Detection Strategies

• Monitor GitLab authentication logs for abnormal patterns of failed SSH authentication attempts
• Implement network-level monitoring for unusual traffic volumes targeting SSH ports
• Configure alerting thresholds for SSH connection rates that exceed normal baseline activity
• Review system resource metrics for unexpected consumption patterns correlated with SSH activity

Monitoring Recommendations

• Deploy intrusion detection systems (IDS) with rules to detect SSH authentication flood patterns
• Establish baseline metrics for normal SSH authentication traffic and alert on significant deviations
• Implement centralized logging to correlate SSH activity across multiple GitLab instances
• Consider using SentinelOne's network visibility capabilities to monitor for anomalous authentication patterns

How to Mitigate CVE-2026-1102

Immediate Actions Required

• Upgrade GitLab CE/EE to version 18.8.2, 18.7.2, or 18.6.4 depending on your current version branch
• Implement network-level rate limiting for SSH connections as a temporary mitigation
• Review firewall rules to restrict SSH access to trusted IP ranges where possible
• Monitor GitLab instances for signs of exploitation while patches are being applied

Patch Information

GitLab has released patched versions that address this vulnerability. Organizations should upgrade to one of the following versions:

• Version 18.8.2 - For organizations running the 18.8.x branch
• Version 18.7.2 - For organizations running the 18.7.x branch
• Version 18.6.4 - For organizations running versions 12.3 through 18.6.x

For detailed patch information, refer to the GitLab Patch Release Announcement and the GitLab Issue Discussion.

Workarounds

• Configure firewall rules to limit SSH access to known, trusted IP addresses or ranges
• Implement rate limiting at the network perimeter for SSH connections to GitLab servers
• Consider temporarily disabling SSH access and using HTTPS for Git operations until patches can be applied
• Deploy a reverse proxy or load balancer with connection rate limiting capabilities in front of GitLab

# Example: Rate limiting SSH connections using iptables
# Limit new SSH connections to 10 per minute per source IP
iptables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --set
iptables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --update --seconds 60 --hitcount 10 -j DROP