MediumCVE-2026-123635

    Refused calls drain the HTTP/2 connection flow-control window in elixir-grpc grpc_server (CVE-2026-123635)

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

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    What is affected, what to do

    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.

    Update Elixir-grpc Grpc Server to version 1.1.0.

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

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

    Metrics

    6.3

    XIEM Effective CVSS

    Highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v4

    6.3

    CVSS v4

    Severity Medium on the scale from 0 to 10.

    Source: CVE.org, OSV, EUVD

    —

    EPSS score

    No value is available for this vulnerability.

    Show all metrics
    Severity
    Medium
    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
    61.50 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
    6.3 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
    6.3
    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
    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-772

    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
    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    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

    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.

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

    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_server
    • 1.0.0 – < 1.1.0
    • 1.1.0
    hexgrpc_server
    • 1.0.5
    • 1.0.4
    • 1.0.1
    • 1.0.2
    • 1.0.0
    • 1.0.6
    • 1.0.3
    • —
    • —
    • —
    • —
    • 1.1.0
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-772Missing Release of Resource after Effective Lifetime

      Base

      The product does not release a resource after its effective lifetime has ended, i.e., after the resource is no longer needed.

      Entry at MITRE CWE-772

    References & sources

    • github.comRefused calls drain the HTTP/2 connection flow-control window in elixir-grpc grpc_servereuvd, Vendor advisory, related, advisory
    • cna.erlef.orgEEF CNA record for CVE-2026-123635euvd, related, web
    • OSV (Open Source Vulnerabilities)OSV record EEF-CVE-2026-123635euvd, related
    • github.comIntroducing commit 0332faa in elixir-grpc/grpceuvd, related, web
    • github.comFix commit 61a7194 in elixir-grpc/grpceuvd, Patch, fix
    • hex.pmpackages/grpc_serverpackage

    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. ReceivedEEF

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

      Weakness type: CWE-772

      Description added or changed

      Show 9 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      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.
      CVSSadded
      —
      AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/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-772
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/123xxx/CVE-2026-123635.json">CVE-2026-123635</a>
      Referenceadded
      —
      https://cna.erlef.org/cves/CVE-2026-123635.html
      Referenceadded
      —
      https://github.com/elixir-grpc/grpc/commit/0332faae5f5e132314794dbfdae5edecbccea292
      Referenceadded
      —
      https://github.com/elixir-grpc/grpc/commit/61a71948e6e7b95efb27d48e7084c764503cc802
      Referenceadded
      —
      https://github.com/elixir-grpc/grpc/security/advisories/GHSA-7x9q-vvph-rjcr
      Referenceadded
      —
      https://osv.dev/vulnerability/EEF-CVE-2026-123635

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

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