---
id: "CVE-2026-123635"
page: "https://infrastack.ai/live/CVE-2026-123635"
kind: "vulnerability"
aliases: ["CVE-2026-123635"]
title: "elixir-grpc: refused calls stall later calls on a shared HTTP/2 connection"
severity: "medium"
cvss: 6.3
epss: null
exploited: false
status: "open"
category: "package"
products: []
ecosystems: []
tags: ["elixir", "grpc", "grpc_server", "package"]
not_affected_if: ["version-1.1.0-or-later"]
published_at: "2026-11-13T16:17:37+00:00"
first_seen_at: "2026-11-13T16:47:33+00:00"
updated_at: "2026-11-13T16:48:52+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-123635", "first_seen_at": "2026-11-13T16:47:33+00:00"}]
exploit_sources: []
---

# elixir-grpc: refused calls stall later calls on a shared HTTP/2 connection

Link for people: https://infrastack.ai/live/CVE-2026-123635 (this .md is for agents)

A client can send calls that the grpc_server refuses while their request data is still in flight, so the HTTP/2 flow-control window is never returned. After enough refused calls, every later call on that connection stalls until its deadline.

_Summary, check and fix written by a model from the sources; labelled as such._

## How to check

- Check the version of grpc_server in your mix.lock or deps for `grpc_server` (from `1.0.0` to before `1.1.0` is affected).
- Look for grpc_server listening directly to clients on a shared HTTP/2 connection, where a client can send many calls.

## Fix

- grpc_server: move to `1.1.0` or later.

## Timeline

- 2026-11-13T16:47:33+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-123635

## Documents

- [advisory] Vendor advisory: github.com https://github.com/elixir-grpc/grpc/security/advisories/GHSA-7x9q-vvph-rjcr
- [fix] Patch: github.com https://github.com/elixir-grpc/grpc/commit/0332faae5f5e132314794dbfdae5edecbccea292
- [fix] Patch: github.com https://github.com/elixir-grpc/grpc/commit/61a71948e6e7b95efb27d48e7084c764503cc802

## From the sources

Missing Release of Resource after Effective Lifetime vulnerability in elixir-grpc grpc_server allows a client to stall all later calls on a shared HTTP/2 connection via calls that the server refuses while their DATA frames are in flight.

The stream handler grpc_stream_h (grpc_server/src/grpc_stream_h.erl) requests flow from Cowboy only for request data that has arrived. When the server refuses a call early, for example because the body exceeds max_body_size or the method is not implemented, Cowboy drops the DATA frames still in flight for that stream. Their bytes are not returned to the connection flow-control window. After enough refused calls the window is empty. No call on that connection can then send a request body, and each call waits until its deadline. Other connections are not affected.

This issue affects grpc_server: from 1.0.0 before 1.1.0.

---

_Free to read, with fair use of about 60 pages a minute. For higher limits or API access: sales@infrastack.ai_