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CVE-2026-121809 CPU exhaustion via a truncated gRPC message on streaming RPCs in elixir-grpc grpc_server

8.2 highFix available

High (8.2) in elixir-grpc. Fixed in grpc_server 1.1.0.

On this page
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.

Severity

CVSS 4.0

8.2 high
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
CISA's assessment (SSVC)
Exploitation: none · Automatable: no · Technical impact: partial, assessed 2026-11-13. From CISA's Vulnrichment in the CVE List: whether it is exploited, whether exploiting it can be automated, and how much control it gives.
CWEs
CWE-400 Uncontrolled Resource Consumption
CWE-835 Loop with Unreachable Exit Condition (Infinite Loop)
Published
Modified
Assigned by
EEF (CNA)
NVD analysis
Awaiting analysis
Record from
the NVD, synced

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Affected

Versions

From the CNA's record in the CVE List.

ProductAffected
elixir-grpc grpc_serverfrom 1.0.0 before 1.1.0
elixir-grpc grpcfrom 0.3.1 before 1.0.0

Fix and patched versions

  • grpc_server (Hex): fixed in 1.1.0
  • grpc (Hex): fixed in 1.0.0

Packages (OSV)

AdvisoryEcosystemPackageAffectedFixed in
EEF-CVE-2026-121809Hexgrpc_server>=1.0.0 <1.1.01.1.0
EEF-CVE-2026-121809Hexgrpc>=0.3.1 <1.0.01.0.0
EEF-CVE-2026-121809v1.0.6, v1.0.3, v1.0.0no fix published
EEF-CVE-2026-121809v0.11.2, v0.8.1, v0.8.0, v0.7.0, v0.6.0 and 5 moreno fix published

Attack patterns (CAPEC)

  • CAPEC-147 XML Ping of the Death Likelihood: Low · Severity: Medium
  • CAPEC-227 Sustained Client Engagement
  • CAPEC-492 Regular Expression Exponential Blowup

The attack patterns MITRE's CAPEC relates to this record's weaknesses, as MITRE names them. Credits.

References

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