CVE-2026-0752: 
GitLab vulnerability analysis and mitigation

CVE-2026-0752 is a Cross-Site Scripting (XSS) vulnerability in GitLab CE/EE affecting the Mermaid sandbox UI that allows unauthenticated attackers to inject arbitrary scripts under certain circumstances. It affects all GitLab CE/EE versions from 16.2 before 18.7.5, 18.8 before 18.8.5, and 18.9 before 18.9.1. The vulnerability was disclosed on February 25, 2026, and patched the same day. GitLab (CNA) assigned a CVSS v3.1 score of 8.0 (High), while NVD assessed it at 6.1 (Medium) (GitLab Advisory, NVD).

The vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation — Cross-Site Scripting), rooted in insufficient sanitization of user-supplied input rendered within the Mermaid diagram sandbox UI. An unauthenticated, network-based attacker can craft malicious input that, when processed by the Mermaid sandbox, causes arbitrary JavaScript to execute in the victim's browser. Exploitation requires user interaction (e.g., a victim viewing a page containing the malicious diagram) and occurs under certain unspecified conditions, suggesting the attack surface may be context-dependent. The vulnerability was reported through GitLab's HackerOne bug bounty program by researcher 'aphantom' (GitLab Advisory, NVD).

Successful exploitation could allow an attacker to steal user session tokens, perform actions on behalf of authenticated users, or modify content rendered in the victim's browser within the GitLab context. According to GitLab's own CVSS assessment, the impact includes high confidentiality and integrity compromise within the changed scope of the Mermaid sandbox environment, with no direct availability impact. Potential attack scenarios include session hijacking, credential theft, or unauthorized actions performed on behalf of users who view a maliciously crafted Mermaid diagram (GitLab Advisory, NVD).

No public proof-of-concept exploit code is known to exist, and there is no evidence of active in-the-wild exploitation at this time. The EPSS score is approximately 0.044%, indicating a low probability of exploitation in the near term. The vulnerability is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog. No threat actor attribution has been reported (Feedly).

1. Reconnaissance: Identify GitLab CE/EE instances running versions 16.2.0–18.7.4, 18.8.0–18.8.4, or 18.9.0 using tools like Shodan, Censys, or by inspecting GitLab's version endpoint (/help or API).
2. Craft malicious Mermaid payload: Construct a Mermaid diagram definition containing an injected script payload that exploits the insufficient input sanitization in the Mermaid sandbox UI (e.g., embedding JavaScript within diagram syntax).
3. Deliver the payload: Insert the malicious Mermaid diagram into a GitLab resource visible to target users, such as a repository README, issue description, merge request, or wiki page — no authentication is required to create certain public-facing content.
4. Trigger victim interaction: Lure an authenticated user (e.g., a project maintainer or administrator) to view the page containing the malicious diagram, causing the injected script to execute in their browser.
5. Achieve objective: The executed script can steal session cookies, exfiltrate tokens, perform API calls on behalf of the victim, or redirect the user to a phishing page (GitLab Advisory, NVD).

• Network: Unexpected outbound HTTP requests from a user's browser to external domains shortly after viewing GitLab pages containing Mermaid diagrams; unusual POST requests to attacker-controlled endpoints carrying session token data.
• Logs: GitLab application logs showing access to pages with Mermaid diagram content by multiple users in quick succession; web server logs showing unusual referrer patterns from GitLab Mermaid-rendered pages.
• Browser/Session: Unexplained session invalidations or concurrent sessions for the same user account; authentication tokens appearing in external server logs.
• File System: Unexpected new SSH keys, personal access tokens, or OAuth applications added to user accounts shortly after viewing Mermaid-containing pages.

GitLab has released patched versions addressing this vulnerability: 18.7.5, 18.8.5, and 18.9.1 for both CE and EE editions, published on February 25, 2026. GitLab strongly recommends that all self-managed installations upgrade to one of these versions immediately; GitLab.com and GitLab Dedicated instances were patched automatically. No configuration-based workaround has been published — upgrading is the only recommended remediation (GitLab Advisory).

The vulnerability was noted in social media posts on Mastodon and Bluesky shortly after disclosure, with community members highlighting it as part of a broader GitLab patch release addressing multiple high-severity issues. Coverage was largely informational, with no significant controversy or debate. Tenable published Nessus detection plugins (IDs 300183 and 300404) to help organizations identify vulnerable instances (Tenable Plugin 300183).