How the CVE Works:
The vulnerability arises due to improper PKCE (Proof Key for Code Exchange) validation in Cloudflare’s workers-oauth-provider. Attackers can bypass PKCE checks by manipulating the OAuth flow, allowing them to intercept authorization codes. If a victim previously authorized an OAuth client and the server auto-approves re-authorizations, an attacker can craft a malicious redirect URI, tricking the victim into visiting it. Since the library fails to validate redirect URIs during the initial authorization phase, the attacker can steal credentials and impersonate the victim.
DailyCVE Form:
Platform: Cloudflare Workers
Version: <0.0.5
Vulnerability: PKCE Bypass
Severity: Critical
Date: 2023-XX-XX
What Undercode Say:
Analytics:
- Attack Vector: Client-side manipulation
- Exploitability: High (requires user interaction)
- Affected Systems: MCP framework using `workers-oauth-provider`
Exploitation:
1. Intercept Auth Code:
GET /auth?response_type=code&client_id=CLIENT&redirect_uri=ATTACKER_URL
2. Bypass PKCE: Omit `code_challenge` or reuse a stolen one.
Mitigation:
1. Update Immediately:
npm update @cloudflare/[email protected]
2. Enforce PKCE:
oauthProvider.usePKCE({ enforce: true });
3. Validate Redirect URIs:
if (!allowedURIs.includes(redirect_uri)) throw new Error("Invalid URI");
Detection:
- Log Analysis:
grep -r "missing PKCE" /var/log/oauth_logs
- Network Monitoring:
tcpdump -i eth0 'port 443 && host oauth-provider'
References:
Sources:
Reported By: github.com
Extra Source Hub:
Undercode
