Can you explain this vulnerability to me?

[{'type': 'paragraph', 'content': "CVE-2026-26022 is a stored Cross-Site Scripting (XSS) vulnerability in Gogs, an open source self-hosted Git service. Prior to version 0.14.2, the application's HTML sanitizer allowed the use of the data: URI scheme without proper restrictions. This allowed authenticated users to inject malicious JavaScript via specially crafted data URI links embedded in raw HTML anchor tags within comments and issue descriptions."}, {'type': 'paragraph', 'content': 'The vulnerability arises because the sanitizer permitted all data: URIs, including unsafe types like data:text/html or SVG images, which can contain executable scripts. Attackers could embed JavaScript payloads in these data URIs, which would execute in the browsers of users viewing the affected content.'}, {'type': 'paragraph', 'content': 'The issue was fixed by restricting the sanitizer to only allow data URIs with safe image MIME types (such as image/png, image/jpeg, image/gif, image/webp, and image/x-icon), effectively blocking executable script payloads embedded in data URIs.'}] [2, 1, 3]

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How can this vulnerability impact me? :

This vulnerability can have serious security impacts if exploited. An attacker who is an authenticated user can inject malicious JavaScript into comments or issue descriptions that other users view.

• Steal authentication cookies and session tokens from users, potentially hijacking their accounts.
• Perform arbitrary actions on behalf of victims, such as modifying repositories or adding collaborators.
• Redirect users to malicious websites, leading to further attacks or phishing.

The vulnerability has a high severity with a CVSS v3.1 base score of 8.7, indicating it is exploitable remotely with low complexity and requires only low privileges (authenticated users) and user interaction (clicking the malicious link).

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How does this vulnerability affect compliance with common standards and regulations (like GDPR, HIPAA)?:

I don't know

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How can this vulnerability be detected on my network or system? Can you suggest some commands?

[{'type': 'paragraph', 'content': 'This vulnerability can be detected by identifying stored Cross-Site Scripting (XSS) payloads embedded in the comment and issue description fields of the Gogs service, specifically those using raw HTML anchor tags with data URI schemes that execute JavaScript.'}, {'type': 'paragraph', 'content': 'A proof-of-concept involves creating or searching for comments or issues containing raw HTML anchor tags with href attributes using data:text/html or other unsafe data URI schemes that embed JavaScript payloads.'}, {'type': 'paragraph', 'content': 'To detect such payloads, you can search the database or exported data for patterns like `<a href="data:text/html;base64,` or other data URI schemes that are not safe image MIME types.'}, {'type': 'list_item', 'content': 'Use grep or similar tools on exported issue/comment data: `grep -r \'<a href="data:text/html\' /path/to/gogs/data`'}, {'type': 'list_item', 'content': 'Query the database for comments or issues containing suspicious data URI links, e.g., using SQL: `SELECT * FROM comments WHERE content LIKE \'%<a href="data:%\'`'}, {'type': 'paragraph', 'content': 'Since the vulnerability requires authenticated users to inject malicious links, monitoring logs for unusual or suspicious comment submissions containing raw HTML with data URIs can also help detect exploitation attempts.'}] [2]

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What immediate steps should I take to mitigate this vulnerability?

[{'type': 'paragraph', 'content': 'The immediate mitigation step is to upgrade Gogs to version 0.14.2 or later, where the vulnerability has been patched.'}, {'type': 'paragraph', 'content': "The patch restricts the HTML sanitizer's allowance of the data URI scheme to only safe image MIME types (image/png, image/jpeg, image/gif, image/webp, image/x-icon), preventing execution of malicious JavaScript embedded in data URIs."}, {'type': 'paragraph', 'content': 'If upgrading immediately is not possible, consider applying the patch that modifies the sanitizer to use a custom validation function to whitelist safe data URI MIME types and reject others.'}, {'type': 'paragraph', 'content': 'Additionally, review and sanitize existing comments and issue descriptions to remove any malicious data URI links.'}, {'type': 'paragraph', 'content': 'Limit user privileges to reduce the risk of authenticated users injecting malicious content, and educate users to avoid clicking suspicious links.'}] [1, 3]

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