CVE-2021-39946
📋 TL;DR
This vulnerability allows attackers to inject malicious scripts through emoji generation in GitLab, leading to cross-site scripting (XSS) attacks. It affects GitLab Community Edition (CE) and Enterprise Edition (EE) users running vulnerable versions. Attackers can execute arbitrary JavaScript in victims' browsers when they view manipulated content.
💻 Affected Systems
- GitLab Community Edition
- GitLab Enterprise Edition
📦 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 →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
Attackers could steal session cookies, perform actions as authenticated users, redirect to malicious sites, or compromise user accounts and data.
Likely Case
Attackers typically steal session tokens to hijack accounts, deface content, or perform limited unauthorized actions within GitLab.
If Mitigated
With proper input validation and output encoding, the attack would fail, preventing script execution while maintaining emoji functionality.
🎯 Exploit Status
Exploitation requires user interaction (viewing malicious content) but the technical barrier is low once the vulnerability is understood.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 14.3.7, 14.4.5, 14.5.3 and later
Vendor Advisory: https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-39946.json
Restart Required: Yes
Instructions:
1. Backup your GitLab instance. 2. Update GitLab to version 14.3.7, 14.4.5, 14.5.3 or later using your package manager. 3. Restart GitLab services. 4. Verify the update completed successfully.
🔧 Temporary Workarounds
Disable user-generated content
allRestrict users from posting content containing emojis or user-generated HTML
Content Security Policy (CSP)
allImplement strict CSP headers to block inline script execution
🧯 If You Can't Patch
- Implement web application firewall (WAF) rules to block XSS payloads in emoji-related requests
- Monitor for suspicious emoji-related activity and implement strict access controls
🔍 How to Verify
Check if Vulnerable:
Check GitLab version: if running 14.3.0-14.3.6, 14.4.0-14.4.4, or 14.5.0-14.5.2, you are vulnerable.Check Version:
sudo gitlab-rake gitlab:env:info | grep 'GitLab Version'Verify Fix Applied:
Confirm GitLab version is 14.3.7+, 14.4.5+, or 14.5.3+ and test emoji functionality works without script execution.📡 Detection & Monitoring
Log Indicators:
- Unusual emoji-related requests with script tags or JavaScript payloads
- Multiple failed login attempts following emoji content views
Network Indicators:
- HTTP requests containing emoji parameters with script payloads
- Outbound connections to suspicious domains after emoji interactions
SIEM Query:
source="gitlab" AND ("emoji" OR "\u" OR "U+*") AND ("<script>" OR "javascript:" OR "onerror=" OR "onload=")🔗 References
- https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-39946.json
- https://gitlab.com/gitlab-org/gitlab/-/issues/345657
- https://hackerone.com/reports/1398305
- https://gitlab.com/gitlab-org/cves/-/blob/master/2021/CVE-2021-39946.json
- https://gitlab.com/gitlab-org/gitlab/-/issues/345657
- https://hackerone.com/reports/1398305
