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  4. CVE 2026 123635 refused calls drain the http2 connection flow
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Back to active CVEs
Medium · CVSS 6.3CVE-2026-123635

Refused calls drain the HTTP/2 connection flow-control window in elixir-grpc grpc_serverCVE-2026-123635

Answer in brief

CVE-2026-123635 records a Medium severity (CVSS 6.3) vulnerability in Refused calls drain the HTTP/2 connection flow-control window in elixir-grpc grpc_server. The current sources do not mark it as known exploited. The current feed maps elixir-grpc/elixir-grpc/grpc (generic), elixir-grpc/grpc_server (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Nov 13, 2026Updated Nov 13, 2026Source checked Nov 13, 2026First seen by HOL Nov 13, 2026Material review Nov 13, 2026
Upstream Advisory

Key facts

Risk
Medium · CVSS 6.3
Exploitation
Not marked as known exploited
Affected software
2 mapped packages or products
Fix availability
Available

Why this deserves its current priority

CVSS is 6.3. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.

Analysis status

Analysis pending evidence review

Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.

Affected scope and exposure questions

The current feed maps elixir-grpc/elixir-grpc/grpc (generic), elixir-grpc/grpc_server (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
PackageAffected rangeFixed version
elixir-grpc/elixir-grpc/grpcgeneric>=0332faae5f5e132314794dbfdae5edecbccea292 <61a71948e6e7b95efb27d48e7084c764503cc80261a71948e6e7b95efb27d48e7084c764503cc802
elixir-grpc/grpc_servergeneric>=1.0.0 <1.1.01.1.0

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for elixir-grpc/elixir-grpc/grpc, elixir-grpc/grpc_server.
  2. 2Review the reported fix. Source-reported workaround: Put a Cowboy stream handler in front of grpc_stream_h with the adapter option stream_handlers: [MyHandler, :grpc_stream_h]. In init/3, the handler calls :cowboy_stream.init/3 and adds a {:flow, size} command when the request has a body, where size is Cowboy's max_frame_size_received (16384 by default). It passes all other callbacks to :cowboy_stream.

Evidence timeline and material changes

  1. Published upstream

    Nov 13, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Nov 13, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Nov 13, 2026

Sources and claim methodology

  • Source referencecna.erlef.org
  • GitHub security advisorygithub.com
  • GitHub security advisorygithub.com
  • GitHub security advisorygithub.com
  • Source referenceosv.dev
Upstream source description

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.

Quoted source text, attributed separately from HOL analysis.

Related CVEs

  • Memory exhaustion via compressed Erlang terms in the elixir-grpc Erlpack codecSame elixir-grpc/elixir-grpc/grpc package
  • CPU exhaustion via a truncated gRPC message on streaming RPCs in elixir-grpc grpc_serverSame elixir-grpc/elixir-grpc/grpc package
  • Path bindings ignored for gRPC Content-Types on transcoded routes in elixir-grpc grpc_serverSame elixir-grpc/elixir-grpc/grpc package
  • Streaming request body limit enforced only after an 8 MB read in elixir-grpc grpc_serverSame elixir-grpc/elixir-grpc/grpc package

Record context

Vulnerability class
Vulnerability
EPSS
Not reported
CWE IDs
CWE-772
Source
CVE List V5
Source checked
Nov 13, 2026
References
5 linked sources
Open source record