fix(security): Add GitHub webhook signature verification

[JuanCS-Dev]

🎯 What: The vulnerability fixed is the lack of signature verification for GitHub webhooks in the Jules router.
⚠️ Risk: The potential impact if left unfixed is that an attacker could spoof GitHub webhook events, potentially triggering unauthorized actions or injecting malicious data.
🛡️ Solution: The fix implements HMAC-SHA256 signature verification using the X-Hub-Signature-256 header and a configured secret (JULES_GITHUB_WEBHOOK_SECRET). It enforces verification if the secret is configured, and logs a warning if not.

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PR created automatically by Jules for task 9120612975598278419 started by @JuanCS-Dev

[google-labs-jules]

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[gemini-code-assist]

Summary of Changes

Hello @JuanCS-Dev, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical security vulnerability by introducing robust signature verification for GitHub webhooks. The change ensures that all incoming webhook events are legitimate and have not been tampered with, thereby safeguarding against potential unauthorized actions or data injection.

Highlights

• Enhanced Security: Implemented HMAC-SHA256 signature verification for GitHub webhooks to prevent spoofing and unauthorized actions.
• Configuration: Introduced JULES_GITHUB_WEBHOOK_SECRET environment variable to store the webhook secret, enabling verification.
• Verification Logic: The system now checks for the X-Hub-Signature-256 header and validates it against the configured secret, raising a 401 error on failure or logging a warning if the secret is not set.

Changelog

• apps/agent-gateway/app/jules/router.py
  • Imported hashlib and hmac for cryptographic operations.
  • Added logic to verify GitHub webhook signatures using HMAC-SHA256.
  • Included error handling for missing or invalid signatures, returning a 401 status.
  • Implemented a warning log if the webhook secret is not configured, indicating skipped verification.
• apps/agent-gateway/app/jules/service.py
  • Added github_webhook_secret attribute to the JulesConfig class.
  • Updated the from_env method to load the github_webhook_secret from the JULES_GITHUB_WEBHOOK_SECRET environment variable.

Activity

• PR created automatically by Jules for task 9120612975598278419 started by @JuanCS-Dev.

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[gemini-code-assist]

Code Review

This pull request introduces GitHub webhook signature verification to the Jules router, addressing a security vulnerability. However, the current implementation 'fails open' by skipping verification if the webhook_secret is not configured, leaving the system vulnerable to spoofing attacks. Additionally, there's a critical issue where the request body is read twice, which will cause the webhook handler to fail when a secret is configured.

[gemini-code-assist]

The GitHub webhook signature verification logic currently 'fails open' if github_webhook_secret is not configured, allowing spoofing attacks. This poses a significant security risk. Additionally, the request body stream can only be read once; reading it twice (once for verification and once for JSON parsing) will cause the webhook handler to fail when a secret is configured. The suggested code addresses the 'fail open' vulnerability by enforcing verification and ensures the request body is read only once for signature verification.

Suggested change

	if webhook_secret:
	signature = request.headers.get("X-Hub-Signature-256", "")
	if not signature:
	raise HTTPException(status_code=401, detail="Missing webhook signature")
	body = await request.body()
	expected_signature = "sha256=" + hmac.new(
	webhook_secret.encode("utf-8"),
	body,
	hashlib.sha256
	).hexdigest()
	if not hmac.compare_digest(signature, expected_signature):
	raise HTTPException(status_code=401, detail="Invalid webhook signature")
	else:
	logger.warning("GitHub webhook secret not configured - skipping verification")
	if not webhook_secret:
	logger.error("GitHub webhook secret not configured - rejecting request")
	raise HTTPException(status_code=500, detail="Webhook verification not configured")
	signature = request.headers.get("X-Hub-Signature-256", "")
	if not signature:
	raise HTTPException(status_code=401, detail="Missing webhook signature")
	body = await request.body()
	expected_signature = "sha256=" + hmac.new(
	webhook_secret.encode("utf-8"),
	body,
	hashlib.sha256
	).hexdigest()
	if not hmac.compare_digest(signature, expected_signature):
	raise HTTPException(status_code=401, detail="Invalid webhook signature")