Detailed Technical Analysis of HackerOne Report #84601
Overview:
This HackerOne report describes a security vulnerability in Gitlab that allows an attacker to exploit a stored Cross-Site Scripting (XSS) vulnerability. The issue was identified in user profile pages where malicious payloads embedded in the Full Name field could be executed in administrative contexts, leading to potentially serious impacts on the platform.
Key Technical Details:
- Vulnerability Context - Stored XSS:
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Stored XSS Attack occurs when a malicious script is injected into a website's storage (e.g., databases) and later rendered in users' browsers. On Gitlab, this specific XSS was embedded in the profile's Full Name field.
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Injection Point - User Profile Field:
- The user profile section of Gitlab includes various form fields like Full Name, Email, etc. The Full Name field didn't have proper sanitization and allowed HTML/JavaScript code to be stored and rendered. This weakness enabled the stored XSS vulnerability.
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The attacker enters a payload in the Full Name field, which is then stored in the Gitlab database.
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Malicious Payload:
- The payload entered in the Full Name field is structured to execute JavaScript. The report doesn't provide the exact payload, but a typical payload could be something like
<img src=x onerror=alert(1)>or<script>alert('XSS')</script>. -
This payload is injected by navigating to the profile settings and modifying the Full Name field with the malicious code.
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Execution Context - Admin Access:
- Once the payload is saved, any administrative user accessing the affected profile page would inadvertently execute this script.
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Since administrative users generally have extended privileges, this could lead to various impactful actions, including session hijacking, arbitrary actions on behalf of the admin, or stealing sensitive information.
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Payload Storage & Activation:
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Upon saving the profile, whenever an admin views the profile, the stored payload in the Full Name field executes in their context. This point emphasizes the difference between stored XSS and other types, where execution persists until manually removed from data storage.
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Impacts:
- Session Hijacking: Stealing cookies/session tokens of administrative users.
- Privilege Escalation: Performing actions on behalf of an admin, potentially adding new users, changing settings, or escalating own privileges.
- Data Exfiltration: Stealing sensitive data displayed within administrative interfaces or accessible via admin privileges.
Mitigation Strategies:
- Input Sanitization:
- Ensure that input fields undergo thorough sanitization and encoding. This prevents malicious scripts from being interpreted as executable code.
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Use libraries and frameworks that handle this automatically by escaping special characters (e.g.,
<,>,",&). -
Output Encoding:
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Wherever user input is displayed, ensure output encoding is implemented. This means converting characters like
<and>to<and>before rendering on the HTML page. -
Content Security Policy (CSP):
- Implement CSP headers to restrict sources from which scripts can be executed. This can help mitigate the impact even if XSS is introduced.
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Disallow inline JavaScript (
script-src 'self' 'unsafe-inline') to prevent execution of injected script tags. -
Regular Security Audits:
- Frequent code reviews and using automated tools to audit and detect insecure coding practices, focusing on areas handling user-generated content.
Conclusion:
The report highlights a classic stored XSS vulnerability in Gitlab's user profile section. Despite being a common type of vulnerability, its impact can be severe, especially in systems where users possess elevated privileges, like administrative interfaces. Proper input validation and output encoding are essential parts of a secure framework that help mitigate such risks. The detailed approach to injecting and exploiting this issue serves as a potent reminder to developers and security teams of the vulnerabilities inherent in web applications if user inputs are not handled securely.
For full context and additional details, refer to the original HackerOne report here.