CVE-2026-72861
Received Received - Intake

GitHub Webhook Signature Bypass in Appwrite Templates

Publication date: 2026-08-20

Last updated on: 2026-08-20

Assigner: VulnCheck

Description
The github-issue-bot templates in appwrite/templates verify the GitHub webhook signature with an inverted condition. verifyWebhook in node/github-issue-bot/src/github.js and in node-typescript/github-issue-bot/src/github.ts returns "typeof signature !== 'string' || (await verify(...))", so when the X-Hub-Signature-256 header is absent the first operand is true, the logical OR short-circuits, and the function reports success without performing any HMAC verification. main.js rejects a request only when verifyWebhook returns false, so an unauthenticated request carrying no signature passes the check. Processing then continues to postComment, which takes the repository and issue objects directly from the request body, letting the caller direct the deployed function to post a comment on a repository and issue of their choosing using the configured GITHUB_TOKEN, with the issue author login from the body interpolated into the comment text.

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Meta Information

Published
2026-08-20
Last Modified
2026-08-20
Generated
2026-08-21
AI Q&A
2026-08-20
EPSS Evaluated
N/A
NVD
CVE-2026-72861
EUVD
EUVD-2026-63579

Affected Vendors & Products

Showing 4 associated CPEs
Vendor Product Version / Range
appwrite github_issue_bot *
node github_issue_bot *
node_typescript github_issue_bot *
appwrite github-issue-bot to 1.1.3 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-347 The product does not verify, or incorrectly verifies, the cryptographic signature for data.

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Executive Summary

This vulnerability is an authentication bypass in the GitHub webhook verification of Appwrite's github-issue-bot templates. The verifyWebhook function incorrectly uses a logical OR condition that short-circuits when the X-Hub-Signature-256 header is missing, causing it to skip HMAC verification and falsely report success. This allows unauthenticated requests to bypass security checks.

Detection Guidance

Check if your github-issue-bot deployment is running versions 1.1.2 or earlier. Inspect the verifyWebhook function in src/github.js or src/github.ts for the inverted condition 'typeof signature !== 'string' || (await verify(...))'. Monitor logs for requests without X-Hub-Signature-256 headers that are processed as authenticated.

Impact Analysis

An attacker can exploit this to post comments on any GitHub repository and issue of their choosing using the configured GITHUB_TOKEN. They can manipulate comment content by injecting issue author login details from the request body, potentially spreading misinformation or phishing links.

Compliance Impact

This vulnerability allows unauthenticated requests to bypass webhook signature verification, enabling attackers to post arbitrary comments on GitHub issues using the configured GITHUB_TOKEN. This could lead to unauthorized actions, data manipulation, or misinformation, potentially violating compliance requirements for data integrity, access control, and audit logging in standards like GDPR and HIPAA.

Mitigation Strategies

Upgrade to the latest version of github-issue-bot templates beyond 1.1.2. Review and correct the verifyWebhook function logic to ensure proper HMAC verification. Add strict header validation to reject requests missing X-Hub-Signature-256. Rotate GITHUB_TOKEN if compromised.

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