elixir-grpc grpc/grpc_server Cowboy Adapter cowboy.ex GRPC.Server.Adapters.Cowboy.read_stream infinite loop

Summaryinfo

A vulnerability described as problematic has been identified in elixir-grpc grpc and grpc_server. The affected element is the function GRPC.Server.Adapters.Cowboy.read_stream of the file grpc_server/lib/grpc/server/adapters/cowboy.ex of the component Cowboy Adapter. The manipulation results in infinite loop. This vulnerability is known as CVE-2026-121809. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability was found in elixir-grpc grpc and grpc_server (unknown version). It has been classified as problematic. Affected is the function GRPC.Server.Adapters.Cowboy.read_stream of the file grpc_server/lib/grpc/server/adapters/cowboy.ex of the component Cowboy Adapter. The manipulation with an unknown input leads to a infinite loop vulnerability. CWE is classifying the issue as CWE-835. The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop. This is going to have an impact on availability. CVE summarizes:

Loop with Unreachable Exit Condition ('Infinite Loop') vulnerability in elixir-grpc grpc_server and grpc allows unauthenticated attackers to occupy a BEAM scheduler indefinitely via a client-streaming or bidirectional-streaming request whose body ends inside a gRPC message. GRPC.Server.Adapters.Cowboy.read_stream/1 (grpc_server/lib/grpc/server/adapters/cowboy.ex, and the Cowboy adapter in grpc before the package split) asks for more data whenever the buffer does not hold a complete message. Once the request body has ended, every further read returns an empty chunk, so the buffer never changes and the function retries without end. A single 5-byte length prefix sent with END_STREAM keeps one scheduler busy for as long as the connection stays open, and repeated requests exhaust all schedulers. This issue affects grpc_server: from 1.0.0 before 1.1.0; grpc: from 0.3.1 before 1.0.0.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-121809 since 11/13/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1499 by the MITRE ATT&CK project.

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

Website

• Product: https://github.com/elixir-grpc/grpc/

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