Open Redirect Vulnerability in Gogs Prior to 0.14.3

Compliance Impact

The vulnerability in Gogs allows attacker-controlled redirect_to parameters to bypass validation, enabling redirection to arbitrary external sites. This can be exploited to redirect users to phishing or malicious sites after login or other actions.

Such open redirect vulnerabilities can increase the risk of phishing attacks and unauthorized data exposure, which may impact compliance with standards like GDPR and HIPAA that require protection of user data and secure authentication flows.

However, the provided information does not explicitly discuss the direct impact of this vulnerability on compliance with specific regulations such as GDPR or HIPAA.

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Detection Guidance

This vulnerability involves the `redirect_to` parameter in Gogs versions prior to 0.14.3, which can be exploited by crafting URLs that bypass the same-site validation and cause open redirects.

To detect potential exploitation attempts on your network or system, you can monitor HTTP requests to your Gogs instance for suspicious `redirect_to` parameter values that include directory traversal sequences combined with backslashes or unusual URL encodings.

• Look for URLs containing patterns like `/a/../\example.com` or similar sequences in the `redirect_to` parameter.
• Use web server logs or network traffic captures to search for such patterns.

Example commands to search logs for suspicious redirect_to parameters (assuming access logs are in common log format):

• Using grep to find suspicious redirect_to parameters in access logs: ```bash grep -E 'redirect_to=.*(\\|%5C|\.\./)' /var/log/nginx/access.log ```
• Using tcpdump to capture HTTP traffic and filter for suspicious redirect_to parameters: ```bash tcpdump -A -s 0 'tcp port 80 and (((ip[2:2] - ((ip[0]&0xf)<<2)) - ((tcp[12]&0xf0)>>2)) != 0)' | grep -i 'redirect_to=' ```

These commands help identify attempts to exploit the open redirect vulnerability by detecting unusual or malformed redirect URLs that bypass validation.

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Executive Summary

This vulnerability exists in Gogs, an open source self-hosted Git service, prior to version 0.14.3. It is an open redirect vulnerability where attacker-controlled redirect_to parameters can bypass validation checks. The validation function, IsSameSite, only inspects the first two characters of the URL string and fails to properly handle directory traversal sequences followed by backslashes. This allows attackers to redirect users to arbitrary external sites.

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Impact Analysis

This vulnerability can impact users by allowing attackers to redirect them to malicious external websites through manipulated redirect parameters. Such redirections can be used for phishing attacks, malware distribution, or other malicious activities that exploit user trust in the original site.

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Mitigation Strategies

To mitigate this vulnerability, you should upgrade Gogs to version 0.14.3 or later, where the open redirect issue has been fixed.

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