CVE-2026-59157 is a medium-severity (CVSS 6.5) CWE-290 vulnerability in github.com/ncarlier/webhookd. A fix is available for github.com/ncarlier/webhookd — see the affected versions and patch details below.
webhookd: Unrestricted HTTP Header to Shell Variable Injection
Exploitation Status
No confirmed exploitation observed yet
- CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-59157.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-59157 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 396,257 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
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 | 1.22.0go get github.com/ncarlier/webhookd@v1.22.0 |
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, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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.
Frequently Asked Questions
Is CVE-2026-59157 in your dependencies?
Find it across Go, including transitive dependencies.