OAuth2 State Validation Bypass in HedgeDoc

Executive Summary

CVE-2026-58489 is a vulnerability in HedgeDoc, an open-source real-time collaborative markdown notes application. Prior to version 1.11.0, the GitHub Gist export feature had a flaw in its OAuth2 state validation process.

The application generated an OAuth2 'state' value but only checked if it existed rather than verifying it matched the expected value for the user's session. This lack of proper validation allowed an attacker to craft a malicious callback URL containing their own valid GitHub OAuth code.

When a logged-in victim clicked the crafted link, HedgeDoc used the victim's session to select which note to export but used the attacker's authorization code to determine the GitHub account receiving the exported note. This could result in the victim's private, protected, or limited notes being exported directly into a Gist controlled by the attacker.

The issue was fixed in version 1.11.0 of HedgeDoc.

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Detection Guidance

Detecting this vulnerability on your network or system requires checking for the presence of a vulnerable version of HedgeDoc (prior to 1.11.0) and monitoring for suspicious OAuth callback activity.

• Check the installed version of HedgeDoc. If it is prior to 1.11.0, the system is vulnerable. You can verify the version by running the following command if HedgeDoc provides a version check endpoint or by inspecting the application's configuration files or logs.
• Monitor network traffic for unusual OAuth callback requests to the HedgeDoc instance, particularly those with manipulated or unexpected 'state' parameters in the GitHub OAuth flow.
• Review HedgeDoc logs for unexpected GitHub Gist exports or mismatched OAuth state values. Look for entries where the 'state' parameter in the callback does not match the expected session value.

Since this is an application-level vulnerability, there are no specific network commands to detect it directly. Focus on version verification and log analysis.

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Impact Analysis

If you are a user of HedgeDoc versions prior to 1.11.0, this vulnerability could impact you in the following ways:

• An attacker could trick you into clicking a malicious link while you are logged into HedgeDoc.
• Your private, protected, or limited notes could be exported without your knowledge to a GitHub Gist controlled by the attacker.
• Sensitive or confidential information stored in your notes could be exposed to unauthorized parties.

The impact depends on the nature of the notes you store in HedgeDoc. If your notes contain personal, financial, or other sensitive data, the risk of exposure is higher.

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Compliance Impact

This vulnerability could affect compliance with several common standards and regulations, depending on the nature of the data stored in HedgeDoc notes:

• GDPR (General Data Protection Regulation): If the exported notes contain personal data of EU citizens, unauthorized access or disclosure could violate GDPR requirements for data protection and breach notification. Organizations may face fines or legal consequences if they fail to protect personal data adequately.
• HIPAA (Health Insurance Portability and Accountability Act): If the notes contain protected health information (PHI), unauthorized export to an attacker-controlled Gist could constitute a breach under HIPAA. Covered entities and business associates could face penalties for failing to safeguard PHI.
• Other regulations: Depending on the industry or jurisdiction, similar data protection laws (e.g., CCPA, PIPEDA) may also be impacted if sensitive or regulated data is exposed due to this vulnerability.

Organizations using HedgeDoc should assess whether the notes stored in the application contain regulated data and take steps to mitigate the risk, such as updating to the patched version (1.11.0 or later) and reviewing access logs for signs of exploitation.

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Mitigation Strategies

To mitigate this vulnerability, follow these immediate steps:

• Upgrade HedgeDoc to version 1.11.0 or later, as the issue has been fixed in this release. This is the most effective way to resolve the vulnerability.
• If upgrading is not immediately possible, disable the GitHub Gist export functionality in HedgeDoc to prevent exploitation of the OAuth state validation flaw.
• Educate users about the risks of clicking on untrusted links, especially those related to OAuth callbacks or note exports, as this vulnerability relies on user interaction.
• Monitor HedgeDoc instances for any signs of exploitation, such as unexpected Gist exports or unauthorized access to notes.
• Review and revoke any suspicious GitHub OAuth tokens or sessions associated with the HedgeDoc application to ensure attackers cannot maintain access.

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