CVE-2026-59157: Medium severity go/github.com/ncarlier/webhookd vulnerability
Description Before 1.22, if the Basic Auth (htpasswd) middleware was not configured, all incoming HTTP headers were blindly forwarded to the webhook script execution environment as shell variables. While the Basic Auth middleware correctly strips the authentication header (X-WebAuthn-User) from the incoming request before conditionally re-injecting it on successful authentication, disabling Basic Auth left the system vulnerable if deployed behind an unhardened reverse proxy.
Impact If an upstream reverse proxy is not properly hardened to strip client-provided authentication headers, an attacker could manually supply these headers (e.g., X-WebAuthn-User). A webhook script relying on this forwarded header for privilege elevation or identity verification could therefore be exploited to bypass security controls and impersonate other users.
Mitigation The WHDALLOWEDUPSTREAMHEADERS configuration setting has been introduced to enforce a strict allowlist of HTTP headers that can be converted into shell variables.
Additionally, the default behavior has been changed to adhere to the principle of least privilege. It is no longer (allow all). The default allowed headers are now restricted to standard operational headers: Accept,Content-Type,Content-Length,User-Agent,X-Forwarded-For
Administrators relying on upstream authentication proxies must explicitly add their authentication headers (e.g., WHDALLOWEDUPSTREAMHEADERS="Accept,Content-Type,Content-Length,User-Agent,X-Forwarded-For,x-webauthn-user") to ensure they are passed to the scripts securely.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
go/github.com/ncarlier/webhookdto a version that resolves this vulnerability.Fixed in 1.22.0 - Configuration
Set WHD_ALLOWED_UPSTREAM_HEADERS to an explicit allowlist of headers that may be converted into shell variables (e.g., WHD_ALLOWED_UPSTREAM_HEADERS="Accept,Content-Type,Content-Length,User-Agent,X-Forwarded-For,x-webauthn-user").
Webhook script / WHD header forwarding middleware WHD_ALLOWED_UPSTREAM_HEADERS = Accept,Content-Type,Content-Length,User-Agent,X-Forwarded-For,x-webauthn-user - Configuration
Ensure the Basic Auth (htpasswd) middleware is configured; when Basic Auth is disabled, incoming HTTP headers can be blindly forwarded as shell variables if the system is behind an unhardened reverse proxy.
Webhook script / WHD header forwarding middleware Basic Auth (htpasswd) middleware = enabled - Compensating control
Harden the upstream reverse proxy to strip client-provided authentication headers (e.g., X-WebAuthn-User) so an attacker cannot manually supply them when forwarding to the webhook execution environment.
Event History
Frequently Asked Questions
Which deployments are exposed to this issue?
Deployments running versions before 1.22 are exposed when the Basic Auth middleware is not configured and the application is behind a reverse proxy that permits client-supplied authentication headers to pass through. Exploitation is consequential where webhook scripts trust forwarded headers for identity verification or privilege elevation.
What does an attacker need to exploit it?
An attacker needs network access to send an HTTP request through an upstream reverse proxy that does not strip client-provided authentication headers. They can supply a header such as X-WebAuthn-User, which may be forwarded into the webhook script environment as a shell variable.
What can be done if upgrading is not immediately possible?
Harden the upstream reverse proxy to strip client-provided authentication headers before requests reach the service. Configure WHD_ALLOWED_UPSTREAM_HEADERS as a strict allowlist so only required headers can be converted into shell variables.
How can an operator assess whether a deployment may already be affected?
Check whether the deployment is running a version before 1.22, has Basic Auth disabled, and accepts requests through a reverse proxy that forwards client-controlled authentication headers. Review webhook scripts for reliance on forwarded headers, particularly X-WebAuthn-User, to establish identity or privileges.