MediumCVE-2026-109821

    Unbounded port parsing in URI.parse/1 enables CPU exhaustion denial of service in Elixir (CVE-2026-109821)

    Published Last modified Sources: Msrc Update Guide, CVE.org, OSV

    Share

    What is affected, what to do

    Improper Validation of Specified Quantity in Input vulnerability in the Elixir standard library's URI module allows an attacker who supplies a URL to cause a denial of service through CPU exhaustion. URI.parse/1 converts the port component with String.to_integer/1 in split_authority/1 (lib/elixir/lib/uri.ex) without bounding its length, so a port of up to 1,262,592 decimal digits produces a bignum of that size and a longer one raises SystemLimitError.

    Update Elixir to version 1.18.6, Elixir to version 1.19.7, Elixir to version 1.20.5.

    Affected
    • Elixir lt 0.5.0..1.18.6
    • Elixir lt 1.19.0-rc.0..1.19.7
    • Elixir lt 1.20.0-rc.0..1.20.5
    Fixed in
    • Elixir 1.18.6
    • Elixir 1.19.7
    • Elixir 1.20.5

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

    Metrics

    6.3

    Priority

    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: Msrc Update Guide, CVE.org, OSV

    0.5 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 42.6

    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
    75.99 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
    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
    0.5 %
    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
    42.6
    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: proof of concept · not automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 30 October 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-1284

    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

    Improper Validation of Specified Quantity in Input vulnerability in the Elixir standard library's URI module allows an attacker who supplies a URL to cause a denial of service through CPU exhaustion. URI.parse/1 converts the port component with String.to_integer/1 in split_authority/1 (lib/elixir/lib/uri.ex) without bounding its length, so a port of up to 1,262,592 decimal digits produces a bignum of that size and a longer one raises SystemLimitError. Rendering the parsed URI back to text (URI.to_string/1, inspect/1, logging, error formatting) converts the bignum with :erlang.integer_to_binary/1, which is quadratic on Erlang/OTP 27, 28 and 29.0: a 400,000-digit port renders in about 2.6 seconds and a 1 MB port in about 18 seconds. Ports above 65535 are also accepted. This issue affects elixir: from 0.5.0 before 1.18.6, from 1.19.0-rc.0 before 1.19.7, and from 1.20.0-rc.0 before 1.20.5.

    Source: Microsoft Security Update Guide, NVD (NIST), cvelistv5, 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-langelixir
    • 0.5.0 – < 1.18.6
    • 1.19.0-rc.0 – < 1.19.7
    • 1.20.0-rc.0 – < 1.20.5
    • 1.18.6
    • 1.19.7
    • 1.20.5

    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-1284Improper Validation of Specified Quantity in Input

      Base

      The product receives input that is expected to specify a quantity (such as size or length), but it does not validate or incorrectly validates that the quantity has the required properties.

      Entry at MITRE CWE-1284

    References & sources

    • github.comUnbounded port parsing in URI.parse/1 enables CPU exhaustion denial of serviceadvisory, Vendor advisory, related
    • cna.erlef.orgEEF CNA record for CVE-2026-109821web, related
    • github.comErlang/OTP advisory for the same issue in uri_stringweb, related
    • github.comIntroducing commit 3980182 in elixir-lang/elixirweb, related
    • github.comFix commit 9a39d64 in elixir-lang/elixirfix, Patch
    • github.comFix commit b70f33a in elixir-lang/elixirfix, Patch
    • github.comFix commit 07d9abc in elixir-lang/elixirfix, Patch
    • github.comFix commit d879b39 in elixir-lang/elixirfix, Patch
    • OSV (Open Source Vulnerabilities)OSV record EEF-CVE-2026-109821related

    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: proof of concept, automatable: no

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/elixir-lang/elixir/security/advisories/GHSA-327h-97cv-59xg
      SSVC assessmentadded
      —
      {"id":"CVE-2026-109821","role":"CISA Coordinator","options":[{"exploitation":"poc"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-10-30T16:52:15.736711Z"}

      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:L/SC:N/SI:N/SA:N

      Weakness type: CWE-400, CWE-1284

      Description added or changed

      Show 14 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      Improper Validation of Specified Quantity in Input vulnerability in the Elixir standard library's URI module allows an attacker who supplies a URL to cause a denial of service through CPU exhaustion. URI.parse/1 converts the port component with String.to_integer/1 in split_authority/1 (lib/elixir/lib/uri.ex) without bounding its length, so a port of up to 1,262,592 decimal digits produces a bignum of that size and a longer one raises SystemLimitError. Rendering the parsed URI back to text (URI.to_string/1, inspect/1, logging, error formatting) converts the bignum with :erlang.integer_to_binary/1, which is quadratic on Erlang/OTP 27, 28 and 29.0: a 400,000-digit port renders in about 2.6 seconds and a 1 MB port in about 18 seconds. Ports above 65535 are also accepted. This issue affects elixir: from 0.5.0 before 1.18.6, from 1.19.0-rc.0 before 1.19.7, and from 1.20.0-rc.0 before 1.20.5.
      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-400
      Weakness type (CWE)added
      —
      CWE-1284
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/109xxx/CVE-2026-109821.json">CVE-2026-109821</a>
      Referenceadded
      —
      https://cna.erlef.org/cves/CVE-2026-109821.html
      Referenceadded
      —
      https://github.com/elixir-lang/elixir/commit/07d9abc3f3ac4c8d2ba8384bd102b6d6205b08b7
      Referenceadded
      —
      https://github.com/elixir-lang/elixir/commit/39801821eef2d06524e5ebf5a0e4b3c380ad23ae
      Referenceadded
      —
      https://github.com/elixir-lang/elixir/commit/9a39d64a4473d02681c486bc70681c972479d32b
      Referenceadded
      —
      https://github.com/elixir-lang/elixir/commit/b70f33a591b6ab8eb0fa4a7e00bac1c2ed4e0d58
      Referenceadded
      —
      https://github.com/elixir-lang/elixir/commit/d879b39d778fec2f475689573d5672720c4f2a21
      Referenceadded
      —
      https://github.com/elixir-lang/elixir/security/advisories/GHSA-327h-97cv-59xg
      Referenceadded
      —
      https://github.com/erlang/otp/security/advisories/GHSA-8qw4-2chm-mvj2
      Referenceadded
      —
      https://osv.dev/vulnerability/EEF-CVE-2026-109821

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

    Embed badge

    Show the severity and KEV status of this vulnerability on your site – with a link back here. The image is updated hourly.

    Badge preview for CVE-2026-109821
    <a href="https://intel.neosec.eu/en/cve/CVE-2026-109821"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-109821.svg?lang=en" alt="CVE-2026-109821 – NEOSEC Intel" height="20"></a>