HighCVE-2025-13836

    Excessive read buffering DoS in http.client (CVE-2025-13836)

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

    What is affected, what to do

    When reading an HTTP response from a server, if no read amount is specified, the default behavior will be to use Content-Length. This allows a malicious server to cause the client to read large amounts of data into memory, potentially causing OOM or other DoS.

    Update Python Software Foundation CPython to version 3.10.20, Python Software Foundation CPython to version 3.11.15, Python Software Foundation CPython to version 3.12.13.

    Affected
    • Python Software Foundation CPython lt *..3.10.20
    • Python Software Foundation CPython lt 3.11.0..3.11.15
    • Python Software Foundation CPython lt 3.12.0..3.12.13
    • Python Software Foundation CPython lt 3.13.0..3.13.11
    • Python Software Foundation CPython lt 3.14.0..3.14.1
    • Python Software Foundation CPython lt 3.15.0a1..3.15.0a3
    Fixed in
    • Python Software Foundation CPython 3.10.20
    • Python Software Foundation CPython 3.11.15
    • Python Software Foundation CPython 3.12.13
    • Python Software Foundation CPython 3.13.11
    • Python Software Foundation CPython 3.14.1
    • Python Software Foundation CPython 3.15.0a3

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

    Metrics

    7.5

    Priority

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

    Source: NVD, CVSS v3

    7.5

    CVSS v3

    Severity High on the scale from 0 to 10.

    Source: Red Hat, SUSE, Debian LTS, OSV, CVE.org, Msrc Update Guide, BSI

    1.6 %

    EPSS score

    Moderate — model estimates 1-10% exploitation likelihood.

    Source: FIRST EPSS, percentile 76.1

    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
    96.31 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
    7.5 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
    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
    1.6 %
    Moderate — model estimates 1-10% 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
    76.1
    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

    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

    When reading an HTTP response from a server, if no read amount is specified, the default behavior will be to use Content-Length. This allows a malicious server to cause the client to read large amounts of data into memory, potentially causing OOM or other DoS.

    Source: redhat_csaf, suse_csaf, Debian LTS Advisories, OSV (Open Source Vulnerabilities), cvelistv5, NVD (NIST), CVE.org (MITRE), Microsoft Security Update Guide, BSI WID Portal, BSI CSAF

    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
    Python Software FoundationCPython
    • 3.12.0 – < 3.12.13
    • < 3.10.20
    • 3.15.0a1 – < 3.15.0a3
    • 3.11.0 – < 3.11.15
    • 3.13.0 – < 3.13.11
    • 3.14.0 – < 3.14.1
    • 3.12.13
    • 3.10.20
    • 3.15.0a3
    • 3.11.15
    • 3.13.11
    • 3.14.1
    pythonpython
    • 3.13.0 – < 3.13.11
    • < 3.10.20
    • 3.15.0
    • 3.12.0 – < 3.12.13
    • 3.14.0
    • 3.11.0 – < 3.11.15
    • 3.13.11
    • 3.10.20
    • —
    • 3.12.13
    • —
    • 3.11.15
    Distribution and container packages (4)

    Downstream packages (e.g. Bitnami, Debian, Ubuntu, Red Hat). Versions refer to the distribution, not the vendor.

    Distribution and container packages
    Affected versionsFixed in
    bitnamipython-min
    • 3.13.0
    • 3.12.0
    • 3.14.0
    • 3.11.0
    • —
    • —
    • —
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianpython3.9bullseye

    References & sources

    • github.compython/cpython/issues/119451report, Issue tracking
    • github.compython/cpython/pull/119454web, Patch
    • github.compython/cpython/commit/4ce27904b597c77d74dd93f2c912676021a99155fix, Patch
    • github.compython/cpython/commit/5a4c4a033a4a54481be6870aa1896fad732555b5fix, Patch
    • mail.python.orgarchives/list/security-announce@python.org/thread/OQ6G7MKRQIS3O…advisory, Vendor advisory
    • github.compython/cpython/commit/289f29b0fe38baf2d7cb5854f4bb573cc34a6a15fix, Patch
    • github.compython/cpython/commit/14b1fdb0a94b96f86fc7b86671ea9582b8676628fix, Patch
    • github.compython/cpython/commit/5dc101675fd22918facbbe0fecdc821502beaaf0fix, Patch
    • github.compython/cpython/commit/afc40bdd3dd71f343fd9016f6d8eebbacbd6587cfix, Patch
    • NVD (NIST)vuln/detail/CVE-2025-13836web

    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 modifiedpython.org

      Show 27 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/python/cpython/commit/14b1fdb0a94b96f86fc7b86671ea9582b8676628
      Referenceadded
      —
      https://github.com/python/cpython/commit/289f29b0fe38baf2d7cb5854f4bb573cc34a6a15
      Referenceadded
      —
      https://github.com/python/cpython/commit/4ce27904b597c77d74dd93f2c912676021a99155
      Referenceadded
      —
      https://github.com/python/cpython/commit/5a4c4a033a4a54481be6870aa1896fad732555b5
      Referenceadded
      —
      https://github.com/python/cpython/commit/5dc101675fd22918facbbe0fecdc821502beaaf0
      Referenceadded
      —
      https://github.com/python/cpython/commit/afc40bdd3dd71f343fd9016f6d8eebbacbd6587c
      Referenceadded
      —
      https://github.com/python/cpython/issues/119451
      Referenceadded
      —
      https://github.com/python/cpython/pull/119454
      Referenceadded
      —
      https://mail.python.org/archives/list/security-announce@python.org/thread/OQ6G7MKRQIS3OAREC3HNG3D2DPOU34XO/
      Referenceremoved
      https://github.com/python/cpython/commit/14b1fdb0a94b96f86fc7b86671ea9582b8676628
      —
      Referenceremoved
      https://github.com/python/cpython/commit/289f29b0fe38baf2d7cb5854f4bb573cc34a6a15
      —
      Referenceremoved
      https://github.com/python/cpython/commit/4ce27904b597c77d74dd93f2c912676021a99155
      —
      Referenceremoved
      https://github.com/python/cpython/commit/5a4c4a033a4a54481be6870aa1896fad732555b5
      —
      Referenceremoved
      https://github.com/python/cpython/commit/5dc101675fd22918facbbe0fecdc821502beaaf0
      —
      Referenceremoved
      https://github.com/python/cpython/commit/afc40bdd3dd71f343fd9016f6d8eebbacbd6587c
      —
      Referenceremoved
      https://github.com/python/cpython/issues/119451
      —
      Referenceremoved
      https://github.com/python/cpython/pull/119454
      —
      Referenceremoved
      https://mail.python.org/archives/list/security-announce@python.org/thread/OQ6G7MKRQIS3OAREC3HNG3D2DPOU34XO/
      —
      Reference typeremoved
      https://github.com/python/cpython/commit/14b1fdb0a94b96f86fc7b86671ea9582b8676628 Types: Patch
      —
      Reference typeremoved
      https://github.com/python/cpython/commit/289f29b0fe38baf2d7cb5854f4bb573cc34a6a15 Types: Patch
      —
      Reference typeremoved
      https://github.com/python/cpython/commit/4ce27904b597c77d74dd93f2c912676021a99155 Types: Patch
      —
      Reference typeremoved
      https://github.com/python/cpython/commit/5a4c4a033a4a54481be6870aa1896fad732555b5 Types: Patch
      —
      Reference typeremoved
      https://github.com/python/cpython/commit/5dc101675fd22918facbbe0fecdc821502beaaf0 Types: Patch
      —
      Reference typeremoved
      https://github.com/python/cpython/commit/afc40bdd3dd71f343fd9016f6d8eebbacbd6587c Types: Patch
      —
      Reference typeremoved
      https://github.com/python/cpython/issues/119451 Types: Issue Tracking, Patch
      —
      Reference typeremoved
      https://github.com/python/cpython/pull/119454 Types: Issue Tracking, Patch
      —
      Reference typeremoved
      https://mail.python.org/archives/list/security-announce@python.org/thread/OQ6G7MKRQIS3OAREC3HNG3D2DPOU34XO/ Types: Vendor Advisory
      —

      Source identifier: cna@python.org

    2. 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 assessmentchanged
      {"id":"CVE-2025-13836","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2025-12-01T18:32:37.506031Z"}
      {"id":"CVE-2025-13836","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2025-12-01T18:32:37.506031Z"}

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

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