HighCVE-2026-97689

    urllib3: HTTPResponse.stream()/read_chunked() buffers an unbounded chunk-size line into memory (CVE-2026-97689)

    Published Last modified Sources: Red Hat, Msrc Update Guide, SUSE, Ubuntu, CVE.org, OSV, Hersteller, BSI

    What is affected, what to do

    A flaw was found in urllib3. This flaw allows a Denial of Service (DoS) through unbounded memory allocation when parsing chunk-encoded responses.

    Update urllib3 to version 2.8.0.

    Affected
    • Urllib3 gte 1.10.3, < 2.8.0..*

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

    Metrics

    8.9

    Priority

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

    Source: Vendor (CNA), CVSS v4

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Red Hat, Msrc Update Guide, SUSE, Ubuntu, CVE.org, OSV, Hersteller, BSI

    0.3 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 25.4

    Show all metrics
    Severity
    High
    Priority score

    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
    79.61
    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
    8.9
    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
    8.9
    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“.

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    0.3 %
    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
    25.4
    Elevated — this CVE ranks above at least 10% of all CVEs scored today.
    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-770

    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

    A flaw was found in urllib3. This flaw allows a Denial of Service (DoS) through unbounded memory allocation when parsing chunk-encoded responses. A malicious server can send an excessively long chunk-size line without a newline, exhausting client memory and terminating the application.

    Source: redhat_csaf, Microsoft Security Update Guide, suse_csaf, Ubuntu Security Notices, NVD (NIST), OSV (Open Source Vulnerabilities), GitHub Security Advisories, cvelistv5, BSI CSAF, BSI WID Portal

    Affected products

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

    Affected products
    VendorProductAffected versionsFixed in
    urllib3urllib3
    • ≥ 1.10.3, < 2.8.0
    • —
    pythonurllib3
    • 1.10.3 – < 2.8.0
    • 2.8.0
    Red HatEnterprise Linux
    • 10
    • 9
    • —
    • —

    Affected operating systems

    Affected operating systems
    FamilyVendorProductVersion
    Linuxubuntupython-urllib3bionic
    Linuxubuntupython-urllib3focal
    Linuxubuntupython-urllib3jammy
    Linuxubuntupython-urllib3noble
    Linuxubuntupython-urllib3resolute

    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

    Reanalysis & status changes

    Chronological NVD audit events for this CVE — reanalyses, CVSS updates, CPE diffs.

    1. Initial Analysisnvd@nist.gov

      • CVSS V3.1: after AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
      • CPE Configuration: after OR *cpe:2.3:a:python:urllib3:*:*:*:*:*:*:*:* versions from (including) 1.10.3 up to (excluding) 2.8.0
      • Reference Type: after GitHub, Inc.: https://github.com/urllib3/urllib3/commit/cd770b059b543be29298ea5c52afb0b1b090f5ed Types: Patch
      • Reference Type: after GitHub, Inc.: https://github.com/urllib3/urllib3/releases/tag/2.8.0 Types: Release Notes

    2. CVE Modified134c704f-9b21-4f2e-91b3-4a467353bcc0

      • SSVC: after {"id":"CVE-2026-97689","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalI…

    3. New CVE Receivedsecurity-advisories@github.com

      • Description: after urllib3 is an HTTP client library for Python. From 1.10.3 until 2.8.0, the HTTPResponse.read_chunked and HTTPResponse.stream methods can allocate unbounded memory because the streaming chunk parser buffers the chunk-size field until newline or EOF without a length bound. The trigger is that a malicious server returns Transfer-Encoding: chunked followed by a very long run of bytes without a newline. The attack mechanism is that a malicious HTTP server sends a very long unterminated chunk-size line. The impact is that unbounded memory allocation can exhaust the client process. This issue is fixed in version 2.8.0.
      • CVSS V4.0: after AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:H/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
      • CWE: after CWE-770
      • Affected: after New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/97xxx/CVE-2026-97689.json">CVE-2026-97689</a>