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This vulnerability affects webhook systems prior to version 1.22. When the Basic Auth (htpasswd) middleware is not configured, the system blindly forwards all incoming HTTP headers to the webhook script execution environment as shell variables. The Basic Auth middleware normally strips the authentication header (X-WebAuthn-User) from incoming requests before conditionally re-injecting it upon successful authentication. However, when Basic Auth is disabled, this protection mechanism is absent, leaving the system vulnerable if deployed behind an unhardened reverse proxy. An attacker can manually supply authentication headers such as X-WebAuthn-User, and if a webhook script relies on this forwarded header for privilege elevation or identity verification, the attacker can bypass security controls and impersonate other users. The vulnerability stems from the lack of header sanitization when the authentication middleware is not active, combined with the default behavior of allowing all headers to be converted into shell variables. This creates a dangerous situation where client-controlled input directly influences the execution environment of webhook scripts. The fix introduces the WHD_ALLOWED_UPSTREAM_HEADERS configuration setting to enforce a strict allowlist of HTTP headers that can be converted into shell variables, and changes the default behavior from allowing all headers to restricting them to standard operational headers only.
DailyCVE Form:
Platform: Webhook Server
Version: Before 1.22
Vulnerability: Header Injection
Severity: Critical
date: Not Specified
Prediction: Fixed in 1.22
What Undercode Say:
Analytics:
Check current header configuration:
grep -r "WHD_ALLOWED_UPSTREAM_HEADERS" /etc/webhook/
Verify reverse proxy header handling:
curl -H "X-WebAuthn-User: admin" http://target/webhook/script
Test header forwarding behavior:
curl -X POST -H "X-WebAuthn-User: attacker" -d "payload" http://target/webhook/endpoint
Inspect environment variables in webhook script:
env | grep -i webauthn
Configuration example for secure deployment:
WHD_ALLOWED_UPSTREAM_HEADERS="Accept,Content-Type,Content-Length,User-Agent,X-Forwarded-For,x-webauthn-user"
How Exploit: (Educational Purposes!)
An attacker identifies a target running a vulnerable webhook server version prior to 1.22 with Basic Auth disabled. The attacker crafts an HTTP request containing a forged X-WebAuthn-User header set to an administrative username. If the upstream reverse proxy does not strip this header, the webhook server converts it into a shell variable within the script execution environment. A webhook script that trusts this header for authentication or authorization decisions will grant the attacker elevated privileges, allowing impersonation of legitimate users and unauthorized access to protected functionality.
Protection: from this CVE
Upgrade to version 1.22 or later immediately. Configure the WHD_ALLOWED_UPSTREAM_HEADERS setting to explicitly define which headers are permitted. Harden reverse proxies to strip client-supplied authentication headers before forwarding requests. Implement the principle of least privilege by restricting header forwarding to only essential operational headers. Regularly audit webhook scripts for reliance on forwarded headers for security decisions. Monitor for suspicious header values in incoming requests. Validate and sanitize all headers at the application layer before using them for authentication purposes.
Impact:
Successful exploitation allows attackers to bypass authentication controls, impersonate arbitrary users including administrators, gain unauthorized access to protected resources, execute actions with elevated privileges, compromise the integrity of webhook-triggered operations, potentially achieve lateral movement within the infrastructure, and undermine the entire authentication trust model of the affected system.
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Sources:
Reported By: github.com
Extra Source Hub:
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