HighCVE-2026-56811

    Phoenix: Unbounded channel joins per transport enables DoS over few connections (CVE-2026-56811)

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

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    What is affected, what to do

    Allocation of Resources Without Limits or Throttling vulnerability in phoenixframework phoenix (Phoenix.Socket module) allows an unauthenticated attacker to cause a denial of service against any endpoint that mounts a Phoenix socket with a reachable channel transport (WebSocket or LongPoll). This vulnerability is associated with program files lib/phoenix/socket.ex and program routine 'Elixir.Phoenix.Socket':handle_in/4.

    Update Phoenix Framework Phoenix to version 1.5.15, Phoenix Framework Phoenix to version 1.6.17, Phoenix Framework Phoenix to version 1.7.24.

    Affected
    • Phoenix Framework Phoenix lt 0.11.0..1.5.15
    • Phoenix Framework Phoenix lt 1.6.0-rc.0..1.6.17
    • Phoenix Framework Phoenix lt 1.7.0-rc.0..1.7.24
    • Phoenix Framework Phoenix lt 1.8.0-rc.0..1.8.9
    Fixed in
    • Phoenix Framework Phoenix 1.5.15
    • Phoenix Framework Phoenix 1.6.17
    • Phoenix Framework Phoenix 1.7.24
    • Phoenix Framework Phoenix 1.8.9

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

    Metrics

    8.7

    Priority

    XIEM Effective CVSS: highest available CVSS rating from NVD and vendor data.

    Source: NVD, CVSS v4

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: CVE.org, OSV, Hersteller

    0.8 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 55.8

    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
    88.39 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
    8.7 Methodology
    CVSS v3

    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
    7.5
    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
    8.7
    EPSS score

    The EPSS score is the absolute model output for an individual vulnerability: the estimated probability of real-world exploitation within the next 30 days, expressed as a value between 0 and 1 (i.e. 0 % to 100 %). A score of 0.42 means „the model estimates a 42 % chance of real-world exploitation within 30 days“.

    Read in glossary
    0.8 %
    Low — model estimates < 1% exploitation likelihood.
    EPSS percentile

    The EPSS percentile is the relative position of a vulnerability within all EPSS-scored CVEs, expressed as a value between 0 and 1. A percentile of 0.90 means „this CVE has a higher EPSS score than 90 % of all other scored CVEs“. Unlike the EPSS score, it is not a probability — but a positioning within a ranking.

    Read in glossary
    55.8
    High — this CVE ranks above the median of all CVEs scored today (rank ≥ 36%).
    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 · automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 7 July 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-770

    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

    Allocation of Resources Without Limits or Throttling vulnerability in phoenixframework phoenix (Phoenix.Socket module) allows an unauthenticated attacker to cause a denial of service against any endpoint that mounts a Phoenix socket with a reachable channel transport (WebSocket or LongPoll). This vulnerability is associated with program files lib/phoenix/socket.ex and program routine 'Elixir.Phoenix.Socket':handle_in/4. Phoenix transports do not limit the number of channels that a single transport process may join. Every phx_join message a client sends over one connection starts a persistent channel process, and the socket process accepts an unbounded number of them. A single unauthenticated client can therefore open one WebSocket or LongPoll connection and stream a large number of phx_join messages, spawning hundreds of thousands of channel processes over that one connection and eventually reaching the BEAM maximum process limit. Once the process table is exhausted the virtual machine can no longer start new processes, denying service to legitimate traffic across the whole node. Because the amplification happens inside a single connection, network-layer connection caps and rate limiting do not mitigate it. The fix adds a :max_channels_per_transport option (default 100) that bounds the number of channels a single transport process can join, forcing abusive clients to open many connections instead, where external load balancers and reverse proxies can throttle them. This issue affects phoenix: from 0.11.0 before 1.5.15, from 1.6.0-rc.0 before 1.6.17, from 1.7.0-rc.0 before 1.7.24, and from 1.8.0-rc.0 before 1.8.9.

    Source: cvelistv5, NVD (NIST), OSV (Open Source Vulnerabilities), GitHub Security Advisories, 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
    phoenixframeworkphoenix
    • 1.6.0-rc.0 – < 1.6.17
    • 0.11.0 – < 1.5.15
    • 1.8.0-rc.0 – < 1.8.9
    • 1.7.0-rc.0 – < 1.7.24
    • 1.8.0 – < 1.8.9
    • 1.7.0 – < 1.7.24
    • 1.2.0 – < 1.5.15
    • 1.6.0 – < 1.6.17
    • 1.6.17
    • 1.5.15
    • 1.8.9
    • 1.7.24
    • 1.8.9
    • 1.7.24
    • 1.5.15
    • 1.6.17
    hexphoenix
    • 1.3.0-rc.0
    • 0.13.0
    • 0.16.0
    • 1.5.14
    • 1.0.4
    • 1.1.1
    • 1.2.0-rc.0
    • 1.7.16
    • 1.6.12
    • 1.6.1
    • 1.4.9
    • 1.8.0-rc.0
    • 1.0.1
    • 1.5.8
    • 1.7.5
    • 1.4.1
    • 1.0.6
    • 1.5.2
    • 1.4.0-rc.0
    • 1.5.3
    • 1.4.7
    • 1.2.0-rc.1
    • 1.7.6
    • 1.0.3
    • 1.8.5
    • 1.7.13
    • 1.5.5
    • 1.4.16
    • 1.3.0-rc.1
    • 1.4.6
    • 1.6.0-rc.0
    • 1.6.5
    • 1.4.18
    • 1.4.13
    • 1.5.12
    • 1.4.0-rc.1
    • 1.3.0
    • 1.1.0
    • 1.3.5
    • 1.7.0
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    Vendors and products

    Weakness classes (CWE)

    • CWE-770Allocation of Resources Without Limits or Throttling

      Base

      The product allocates a reusable resource or group of resources on behalf of an actor without imposing any intended restrictions on the size or number of resources that can be allocated.

      Entry at MITRE CWE-770

    References & sources

    • github.comphoenixframework/phoenix/security/advisories/GHSA-6983-jfq8-485wadvisory, Vendor advisory, related, Patch, Vendor advisory
    • cna.erlef.orgEEF CNA record for CVE-2026-56811web, related, Mitigation, Patch, Third-party advisory
    • github.comFix commit c498ba8 in phoenixframework/phoenixfix, Patch, Patch
    • github.comFix commit d19ca0a in phoenixframework/phoenixfix, Patch, Patch
    • github.comFix commit a612100 in phoenixframework/phoenixfix, Patch, Patch
    • github.comFix commit 16e295d in phoenixframework/phoenixfix, Patch, Patch
    • hex.pmpackages/phoenixpackage
    • NVD (NIST)vuln/detail/CVE-2026-56811advisory
    • github.comphoenixframework/phoenixpackage
    • OSV (Open Source Vulnerabilities)OSV record EEF-CVE-2026-56811web, related, Mitigation, Third-party advisory
    • github.comIntroducing commit 14a297e in phoenixframework/phoenixweb, related

    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 modifiedEEF

      Show 22 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://cna.erlef.org/cves/CVE-2026-56811.html
      Referenceadded
      —
      https://github.com/phoenixframework/phoenix/commit/14a297e88023cb280a577962a49a0bbdeef9f4eb
      Referenceadded
      —
      https://github.com/phoenixframework/phoenix/commit/16e295d2fccab185d1292322e2bee5d46c725c8a
      Referenceadded
      —
      https://github.com/phoenixframework/phoenix/commit/a612100cd8a4279091abc1a2ef8fb98a6d01c0a1
      Referenceadded
      —
      https://github.com/phoenixframework/phoenix/commit/c498ba8cf49f6accbbd0c643a5340b58db891218
      Referenceadded
      —
      https://github.com/phoenixframework/phoenix/commit/d19ca0a8d9f82c130b7ed339b9f033433e2dea5e
      Referenceadded
      —
      https://github.com/phoenixframework/phoenix/security/advisories/GHSA-6983-jfq8-485w
      Referenceadded
      —
      https://osv.dev/vulnerability/EEF-CVE-2026-56811
      Referenceremoved
      https://cna.erlef.org/cves/CVE-2026-56811.html
      —
      Referenceremoved
      https://github.com/phoenixframework/phoenix/commit/16e295d2fccab185d1292322e2bee5d46c725c8a
      —
      Referenceremoved
      https://github.com/phoenixframework/phoenix/commit/a612100cd8a4279091abc1a2ef8fb98a6d01c0a1
      —
      Referenceremoved
      https://github.com/phoenixframework/phoenix/commit/c498ba8cf49f6accbbd0c643a5340b58db891218
      —
      Referenceremoved
      https://github.com/phoenixframework/phoenix/commit/d19ca0a8d9f82c130b7ed339b9f033433e2dea5e
      —
      Referenceremoved
      https://github.com/phoenixframework/phoenix/security/advisories/GHSA-6983-jfq8-485w
      —
      Referenceremoved
      https://osv.dev/vulnerability/EEF-CVE-2026-56811
      —
      Reference typeremoved
      https://cna.erlef.org/cves/CVE-2026-56811.html Types: Mitigation, Patch, Third Party Advisory
      —
      Reference typeremoved
      https://github.com/phoenixframework/phoenix/commit/16e295d2fccab185d1292322e2bee5d46c725c8a Types: Patch
      —
      Reference typeremoved
      https://github.com/phoenixframework/phoenix/commit/a612100cd8a4279091abc1a2ef8fb98a6d01c0a1 Types: Patch
      —
      Reference typeremoved
      https://github.com/phoenixframework/phoenix/commit/c498ba8cf49f6accbbd0c643a5340b58db891218 Types: Patch
      —
      Reference typeremoved
      https://github.com/phoenixframework/phoenix/commit/d19ca0a8d9f82c130b7ed339b9f033433e2dea5e Types: Patch
      —
      Reference typeremoved
      https://github.com/phoenixframework/phoenix/security/advisories/GHSA-6983-jfq8-485w Types: Patch, Vendor Advisory
      —
      Reference typeremoved
      https://osv.dev/vulnerability/EEF-CVE-2026-56811 Types: Mitigation, Third Party Advisory
      —

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

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