CVE-2026-59157
MEDIUMCVE-2026-59157 is a medium-severity (CVSS 6.5) vulnerability in github.com/ncarlier/webhookd. O3 Security confirms whether CVE-2026-59157 is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.
webhookd: Unrestricted HTTP Header to Shell Variable Injection
Real-World Exposure
github.com/ncarlier/webhookdReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.
Description
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 WHD_ALLOWED_UPSTREAM_HEADERS 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., WHD_ALLOWED_UPSTREAM_HEADERS="Accept,Content-Type,Content-Length,User-Agent,X-Forwarded-For,x-webauthn-user") to ensure they are passed to the scripts securely.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/ncarlier/webhookd | all versions | 1.22.0 |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/ncarlier/webhookd. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update github.com/ncarlier/webhookd to 1.22.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-59157 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2026-59157 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.
Tailored to CVE-2026-59157. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-59157 in your dependencies?
O3 detects CVE-2026-59157 across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.