GHSA-46wh-3698-f2cxHigh▾ TwilightTraefik: Deny Rule Bypass via Unauthenticated Malicious gRPC Requests in gRPC-Go Dependency (CVE-2026-33186)
▾ Twilight zone — High severity, or a signal on a lesser flaw
impact 41.3 · likelihood 0 · exploitation 0
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Disclosure to exploitation, from the record and what we observed since indexing it.
Disclosed via OSV
Last analysed / modified upstream
There is a potential vulnerability in Traefik due to its dependency on an affected version of gRPC-Go (CVE-2026-33186).
A remote, unauthenticated attacker can send gRPC requests with a malformed HTTP/2 :path pseudo-header omitting the mandatory leading slash (e.g., Service/Method instead of /Service/Method). While the server routes such requests correctly, path-based authorization interceptors evaluate the raw non-canonical path and fail to match "deny" rules, allowing the request to bypass the policy entirely if a fallback "allow" rule is present.
If there are any questions or comments about this advisory, please open an issue.
<details> <summary>Original Description</summary>This CVE hits traefik until Version 3.6.11 and 2.11.41. gRPC-Go has an authorization bypass via missing leading slash in :path
As described in https://github.com/advisories/GHSA-p77j-4mvh-x3m3
Update library version in https://github.com/traefik/traefik/blob/67c64ed9b25fbb90f1086977a62827133a7aa01b/go.mod#L108
Is described in https://github.com/advisories/GHSA-p77j-4mvh-x3m3
</details>github.com/traefik/traefik/v2 < 2.11.42github.com/traefik/traefik/v3 >= 3.0.0-beta3, < 3.6.12github.com/traefik/traefik/v3 >= 3.7.0-ea.1, < 3.7.0-ea.3Upgrade to a patched release:
github.com/traefik/traefik/v2 2.11.42github.com/traefik/traefik/v3 3.6.12github.com/traefik/traefik/v3 3.7.0-ea.3Connected by shared product, vendor, weakness, or advisory.
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