elixir-grpc grpc_server/grpc Transcoding server.ex GRPC.Server.do_handle_request authorization

Summaryinfo

A vulnerability was found in elixir-grpc grpc_server and grpc. It has been rated as critical. The affected element is the function GRPC.Server.do_handle_request of the file grpc_server/lib/grpc/server.ex of the component Transcoding. Performing a manipulation results in authorization. This vulnerability is reported as CVE-2026-124278. The attack is possible to be carried out remotely. No exploit exists.

Detailsinfo

A vulnerability classified as critical has been found in elixir-grpc grpc_server and grpc (version unknown). This affects the function GRPC.Server.do_handle_request of the file grpc_server/lib/grpc/server.ex of the component Transcoding. The manipulation with an unknown input leads to a authorization vulnerability. CWE is classifying the issue as CWE-639. The system's authorization functionality does not prevent one user from gaining access to another user's data or record by modifying the key value identifying the data. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

Authorization Bypass Through User-Controlled Key vulnerability in elixir-grpc grpc_server and grpc allows an attacker to make a handler act on a resource other than the one named in the URL of an HTTP-transcoded route, via a request with a gRPC Content-Type. Only the transcoding clause of GRPC.Server.do_handle_request/4 (grpc_server/lib/grpc/server.ex, and lib/grpc/server.ex before the package split) applies the route's path bindings to the request message. The Cowboy handler picks that clause from the request Content-Type, not from the route. A request to a transcoded URL with application/grpc or application/grpc-web is decoded from the body alone, so every path-bound field takes its value from the body. A gateway, proxy rule or WAF that authorizes on the URL path sees one resource while the handler receives another. This issue affects grpc_server: from 1.0.0 before 1.1.0; grpc: from 0.8.0 before 1.0.0.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-124278 since 11/10/2026. The exploitability is told to be easy. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available. The price for an exploit might be around USD $0-$5k at the moment (estimation calculated on 11/13/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Vendor

• elixir-grpc

Name

• grpc
• grpc_server

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