Envoy Gateway: Authentication Bypass via Improper Input Validation in EnvoyExtensionPolicy Lua Allows Secret Disclosure
Impact
The to_absolute_normalized_path function (security.lua:28-43) does not collapse redundant path separators (// → /). On Linux, //etc/passwd is equivalent to /etc/passwd (POSIX path semantics), but is_critical_path fails to match the double-slash variant because //etc/passwd does not start with /etc/.
This allows Lua code submitted as an EnvoyExtensionPolicy to read arbitrary files from the gateway controller pod's filesystem during Strict validation (the default), including:
* /etc/passwd
* Kubernetes SA tokens via //var/run/secrets/kubernetes.io/serviceaccount/token
* TLS certificates via //certs/...
* Process environment via //proc/self/environ
These credentials can be used to read sensitive information from the K8s API Server or from the Gateway XDS server.
Patches
This has been patched in versions >= v1.7.4 and v1.8.1
- Collapse redundant path separators (
//to/) so double-slash variants like//etc/passwdand//var/run/secrets/...are matched by the critical-path check. - Rewrite the traversal check to reject any
.or..segment in any position and across both separator styles (catches/etc/./passwd,./etc/passwd,/etc/.).
Workarounds
Please refer to theWarning section in Lua docs for measures to reduce risk.Credits
Envoy Gateway thanks @dashingDragon and @Donjon-Cerberus for reporting this issue.