CVE-2026-1456 – This vulnerability allows unauthenticated attac... (How to Fix)

Q: What is the severity of CVE-2026-1456?

CVE-2026-1456 has a CVSS score of 6.5 (MEDIUM). This vulnerability allows unauthenticated attackers to cause denial of service through CPU exhaustion by submitting specially crafted markdown files to GitLab instances. The exponential processing in markdown preview can be triggered remotely, affecting all GitLab CE/EE installations running vulnerable versions. Organizations using affected GitLab versions for source code management are at risk.

📋 TL;DR

This vulnerability allows unauthenticated attackers to cause denial of service through CPU exhaustion by submitting specially crafted markdown files to GitLab instances. The exponential processing in markdown preview can be triggered remotely, affecting all GitLab CE/EE installations running vulnerable versions. Organizations using affected GitLab versions for source code management are at risk.

💻 Affected Systems

Products:

GitLab Community Edition
GitLab Enterprise Edition

Versions: 18.7.0 to 18.7.3, 18.8.0 to 18.8.3

Operating Systems: All

Default Config Vulnerable: ⚠️ Yes

Notes: All deployments with markdown preview functionality enabled are vulnerable. Self-managed and cloud instances both affected.

📦 What is this software?

Gitlab by Gitlab

GitLab is a complete DevOps platform providing source code management, CI/CD pipelines, security scanning, container registry, and collaboration tools used by millions of developers and thousands of enterprises worldwide. As both a cloud-hosted SaaS offering (GitLab.com) and self-managed software, G...

Learn more about Gitlab →

Gitlab by Gitlab

GitLab is a complete DevOps platform providing source code management, CI/CD pipelines, security scanning, container registry, and collaboration tools used by millions of developers and thousands of enterprises worldwide. As both a cloud-hosted SaaS offering (GitLab.com) and self-managed software, G...

Learn more about Gitlab →

Gitlab by Gitlab

GitLab is a complete DevOps platform providing source code management, CI/CD pipelines, security scanning, container registry, and collaboration tools used by millions of developers and thousands of enterprises worldwide. As both a cloud-hosted SaaS offering (GitLab.com) and self-managed software, G...

Learn more about Gitlab →

Gitlab by Gitlab

GitLab is a complete DevOps platform providing source code management, CI/CD pipelines, security scanning, container registry, and collaboration tools used by millions of developers and thousands of enterprises worldwide. As both a cloud-hosted SaaS offering (GitLab.com) and self-managed software, G...

Learn more about Gitlab →

⚠️ Risk & Real-World Impact

🔴

Worst Case

Complete service unavailability due to CPU resource exhaustion, potentially disrupting development workflows, CI/CD pipelines, and code collaboration for extended periods.

🟠

Likely Case

Performance degradation and intermittent service disruptions affecting markdown preview functionality and potentially other GitLab services sharing CPU resources.

🟢

If Mitigated

Minimal impact with proper rate limiting, resource monitoring, and network segmentation in place to detect and block malicious requests.

🌐 Internet-Facing: HIGH

🏢 Internal Only: MEDIUM

🎯 Exploit Status

Public PoC: ✅ No

Weaponized: LIKELY

Unauthenticated Exploit: ⚠️ Yes

Complexity: LOW

Exploitation requires only HTTP access to submit markdown files. No authentication or special privileges needed.

🛠️ Fix & Mitigation

✅ Official Fix

Patch Version: 18.7.4, 18.8.4

Vendor Advisory: https://about.gitlab.com/releases/2026/02/10/patch-release-gitlab-18-8-4-released/

Restart Required: Yes

Instructions:

1. Backup GitLab instance. 2. Update to GitLab 18.7.4 if on 18.7.x series. 3. Update to GitLab 18.8.4 if on 18.8.x series. 4. Restart GitLab services. 5. Verify functionality.

🔧 Temporary Workarounds

Disable markdown preview

all

Temporarily disable markdown preview functionality to prevent exploitation

Edit GitLab configuration to disable markdown processing features

Rate limiting

all

Implement rate limiting on markdown processing endpoints

Configure web server or application firewall to limit requests to /api/v4/markdown and similar endpoints

🧯 If You Can't Patch

Implement strict network controls to limit access to GitLab markdown endpoints
Deploy WAF rules to detect and block patterns of excessive markdown processing requests

🔍 How to Verify

Check if Vulnerable:

Check GitLab version via admin interface or command: sudo gitlab-rake gitlab:env:info

Check Version:

sudo gitlab-rake gitlab:env:info | grep 'GitLab Version'

Verify Fix Applied:

Confirm version is 18.7.4 or higher (for 18.7.x) or 18.8.4 or higher (for 18.8.x)

📡 Detection & Monitoring

Log Indicators:

High CPU usage spikes
Excessive markdown processing requests
Slow response times from /api/v4/markdown endpoints

Network Indicators:

Unusual volume of POST requests to markdown endpoints
Pattern of repeated markdown submissions from single IPs

SIEM Query:

source="gitlab" AND (uri_path="/api/v4/markdown" OR uri_path="/explore/projects") AND status>=200 AND status<300 | stats count by src_ip | where count>100

📊 Metadata

CVE ID: CVE-2026-1456

CVSS v3 Score: 6.5 (MEDIUM)

CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CWE: CWE-770

EPSS Score: 0.03% exploit probability (6.2th percentile)

Published: February 11, 2026

Last Updated: February 12, 2026

🔗 References

https://about.gitlab.com/releases/2026/02/10/patch-release-gitlab-18-8-4-released/ Release Notes,Vendor Advisory
https://gitlab.com/gitlab-org/gitlab/-/issues/587688 Broken Link,Issue Tracking
https://hackerone.com/reports/3517928 Permissions Required

📤 Share & Export

📄 Export Markdown 📋 Export JSON

🔗 Related Vulnerabilities

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