HighCVE-2026-121809

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

    Published Last modified Sources: CVE.org, EUVD, OSV

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    What is affected, what to do

    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.

    Update Elixir-grpc Grpc Server to version 1.1.0, Elixir-grpc Grpc to version 1.0.0.

    Affected
    • Elixir-grpc Grpc Server lt 1.0.0..1.1.0
    • Elixir-grpc Grpc lt 0.3.1..1.0.0
    Fixed in
    • Elixir-grpc Grpc Server 1.1.0
    • Elixir-grpc Grpc 1.0.0

    Not sure whether and how you are affected? Ask a question about this vulnerability

    Metrics

    8.2

    XIEM Effective CVSS

    Highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v4

    8.2

    CVSS v4

    Severity High on the scale from 0 to 10.

    Source: CVE.org, EUVD, OSV

    —

    EPSS score

    No value is available for this vulnerability.

    Show all metrics
    Severity
    High
    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

    Read in glossary
    71.00 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

    Read in glossary
    no public PoC known
    XIEM Effective CVSS

    XIEM® is the tiered managed-security operating model from NEOSEC and a registered trademark of NEOSEC GmbH. It extends classic SIEM — the central collection, normalisation and correlation of security-relevant events — with endpoint forensics, network visibility and deception technology, and consolidates them into three building tiers: Sentry, Orchestrate and Command.

    Read in glossary
    8.2 Methodology
    CVSS v4

    CVSS is the globally established, open standard for assessing the technical severity of a vulnerability on a scale from 0 to 10. It describes how easily a flaw can be exploited and what damage it can cause — but not how likely its actual exploitation is. CVSS and the complementary EPSS deliberately answer different questions.

    Read in glossary
    8.2
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

    Read in glossary
    —
    Published
    CISA assessment (SSVC)
    Exploitation: none known · not automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 13 November 2026
    CWE

    CWE is a catalogue of typical weakness types in software and hardware — such as flawed input validation, unsafe memory handling or poor authentication. Where a CVE names a concrete vulnerability in a concrete product, a CWE describes the underlying class of defect.

    Read in glossary
    CWE-400, CWE-835

    Detection rules

    No NEOSEC detection rule is available for this vulnerability yet.

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

    Read in glossary
    High technical severity: assess and remediate the vulnerability in vulnerability handling under Art. 21(2)(e) NIS2 and document the decision.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

    Read in glossary
    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

    Read in glossary
    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    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.

    Source: cvelistv5, NVD (NIST), ENISA EUVD, OSV (Open Source Vulnerabilities), CVE.org (MITRE)

    Affected products

    The following versions are affected. Older releases of the same product line are also vulnerable unless stated otherwise.

    Affected products
    Affected versionsFixed in
    elixir-grpcgrpc
    • 0.3.1 – < 1.0.0
    • 1.0.0
    elixir-grpcgrpc_server
    • 1.0.0 – < 1.1.0
    • 1.1.0
    hexgrpc
    • 0.11.2
    • 0.10.1
    • 0.3.1
    • 1.0.0-rc.1
    • 0.11.0
    • 0.8.1
    • 0.4.0-alpha.1
    • 0.5.0
    • 0.10.0
    • 0.11.5
    • 0.11.4
    • 0.8.0
    • 0.10.2
    • 0.7.0
    • 0.6.0
    • 0.4.0-alpha.2
    • 0.9.0
    • 0.11.1
    • 0.5.0-beta
    • 0.5.0-beta.1
    • 0.11.3
    • —
    • —
    • 1.0.0
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    • —
    hexgrpc_server
    • 1.0.0
    • 1.0.1
    • 1.0.2
    • 1.0.4
    • 1.0.6
    • 1.0.5
    • 1.0.3
    • 1.1.0
    • —
    • —
    • —
    • —
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-400Uncontrolled Resource Consumption

      Class

      The product does not properly control the allocation and maintenance of a limited resource.

      Entry at MITRE CWE-400

    • CWE-835Loop with Unreachable Exit Condition ('Infinite Loop')

      Base

      The product contains an iteration or loop with an exit condition that cannot be reached, i.e., an infinite loop.

      Entry at MITRE CWE-835

    References & sources

    • github.comCPU exhaustion via a truncated gRPC message on streaming RPCs in elixir-grpc grpc_servereuvd, Vendor advisory, related, advisory
    • cna.erlef.orgEEF CNA record for CVE-2026-121809euvd, related, web
    • OSV (Open Source Vulnerabilities)OSV record EEF-CVE-2026-121809euvd, related
    • github.comIntroducing commit 0332faa in elixir-grpc/grpceuvd, related, web
    • github.comFix commit 38955f1 in elixir-grpc/grpceuvd, Patch, fix
    • github.comIntroducing commit 6d8a09a in elixir-grpc/grpceuvd, related, web
    • hex.pmpackages/grpc_serverpackage
    • hex.pmpackages/grpcpackage

    Changes to this CVE

    Who changed this CVE and when: NVD (analysis, affected products, CVSS), the CVE publisher (CNA) and additional providers such as CISA (ADP).

    1. Record modifiedCISA ADP

      CISA assessment (SSVC): exploitation: none known, automatable: no

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      SSVC assessmentadded
      —
      {"id":"CVE-2026-121809","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-11-13T17:55:12.226355Z"}

      Source identifier: 134c704f-9b21-4f2e-91b3-4a467353bcc0

    2. ReceivedEEF

      CVSS V4.0: AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

      Weakness type: CWE-400, CWE-835

      Description added or changed

      Show 11 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      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.
      CVSSadded
      —
      AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
      Weakness type (CWE)added
      —
      CWE-400
      Weakness type (CWE)added
      —
      CWE-835
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/121xxx/CVE-2026-121809.json">CVE-2026-121809</a>
      Referenceadded
      —
      https://cna.erlef.org/cves/CVE-2026-121809.html
      Referenceadded
      —
      https://github.com/elixir-grpc/grpc/commit/0332faae5f5e132314794dbfdae5edecbccea292
      Referenceadded
      —
      https://github.com/elixir-grpc/grpc/commit/38955f1392cbf08eef231a347348445410455c85
      Referenceadded
      —
      https://github.com/elixir-grpc/grpc/commit/6d8a09ad919e208fb600538ac8b19bd733a04310
      Referenceadded
      —
      https://github.com/elixir-grpc/grpc/security/advisories/GHSA-c2h9-f9cc-27xh
      Referenceadded
      —
      https://osv.dev/vulnerability/EEF-CVE-2026-121809

      Source identifier: 6b3ad84c-e1a6-4bf7-a703-f496b71e49db

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