MediumCVE-2026-12003

    CPython >3.11 Insecure Input Validation resulting in privilege escalation (CVE-2026-12003)

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

    What is affected, what to do

    To allow builds of Python to be run from an in-tree layout (rather than an installed file layout), the VPATH variable is defined at build time and used to locate certain landmarks - specifically, Modules/setup.local. When this landmark is found relative to VPATH relative to the executable, Python assumes it is running in a source tree and generates a different default sys.path.

    Update Python Software Foundation CPython to version 3.11.16, Python Software Foundation CPython to version 3.12.14, Python Software Foundation CPython to version 3.13.15.

    Affected
    • Python Software Foundation CPython lt *..3.11.16
    • Python Software Foundation CPython lt 3.12.0..3.12.14
    • Python Software Foundation CPython lt 3.13.0..3.13.15
    • Python Software Foundation CPython lt 3.14.0..3.14.7
    • Python Software Foundation CPython lt 3.15.0a1..3.15.0b3
    Fixed in
    • Python Software Foundation CPython 3.11.16
    • Python Software Foundation CPython 3.12.14
    • Python Software Foundation CPython 3.13.15
    • Python Software Foundation CPython 3.14.7
    • Python Software Foundation CPython 3.15.0b3

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

    Metrics

    5.3

    Priority

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

    Source: NVD, CVSS v4

    5.3

    CVSS v4

    Severity Medium on the scale from 0 to 10.

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

    0.1 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 3.5

    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
    45.48 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
    5.3 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
    5.3
    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
    0.1 %
    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
    3.5
    Low — this CVE sits in the lower 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
    CISA assessment (SSVC)
    Exploitation: none known · not automatable · Technical impact: total
    Source: CISA Vulnrichment, as of 16 June 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-427

    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

    To allow builds of Python to be run from an in-tree layout (rather than an installed file layout), the VPATH variable is defined at build time and used to locate certain landmarks - specifically, Modules/setup.local. When this landmark is found relative to VPATH relative to the executable, Python assumes it is running in a source tree and generates a different default sys.path. This code remains in release builds, so that release-ready builds can be built in-tree. On Windows, since builds are written to 'PCbuild/', the value of VPATH is set to '..\..', which results in a landmark of '..\..\Modules\setup.local'. This path is outside the install directory of Python, and may have different permissions, potentially allowing a low-privilege user to create the landmark and an alternative `Lib` folder that will be discovered by an otherwise restricted install. Such a setup occurs with the legacy default install location for all users (in the now superseded EXE installer), due to how Windows allows all users to create folders in the root directory of their OS drive. Our recommended mitigation on Windows is to migrate away from the legacy installer and use the new [Python install manager](https://www.python.org/downloads/latest/pymanager/) to install for the current user. Installs where the directory two levels above the Python installation directory have equivalent permissions are unaffected (in general, a per-user install cannot be modified at all by other users, removing any escalation of privilege risk, and could be directly modified by a privileged user, making the potential tampering irrelevant). Alternative mitigations might include preemptively creating and restricting access to a `Modules` directory. Be aware that only 3.13 and 3.14 will receive updated legacy installers - earlier fixes are only provided as sources. Platforms other than Windows allow VPATH to be overridden, but as they don't usually use a separated directory in the build for binaries, are unlikely to have a landmark reference outside of the install directory. The landmark detection involving VPATH is a fallback for when a more specific landmark - .\pybuilddir.txt - is absent, and was included for compatibility. Future releases of Python will no longer include the fallback, and so builds will need to generate or preserve the pybuilddir.txt file in order to work in-tree. This landmark file has been generated on Windows since 3.11, and on other platforms for longer.

    Source: redhat_csaf, BSI WID Portal, BSI CSAF, OSV (Open Source Vulnerabilities), NVD (NIST), Microsoft Security Update Guide, cvelistv5, 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
    Python Software FoundationCPython
    • 3.12.0 – < 3.12.14
    • 3.15.0a1 – < 3.15.0b3
    • 3.13.0 – < 3.13.15
    • 3.14.0 – < 3.14.7
    • < 3.11.16
    • 3.12.14
    • 3.15.0b3
    • 3.13.15
    • 3.14.7
    • 3.11.16
    Open SourcePython
    • Cpython Windows legacy installer
    • Cypthon
    • —
    • —
    Distribution and container packages (3)

    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
    • —
    • —
    • —

    Vendors and products

    Weakness classes (CWE)

    • CWE-427Uncontrolled Search Path Element

      Base

      The product uses a fixed or controlled search path to find resources, but one or more locations in that path can be under the control of unintended actors.

      Entry at MITRE CWE-427

    References & sources

    • github.compython/cpython/pull/151545web, Patch
    • github.compython/cpython/issues/151544report, Issue tracking
    • httpsmail.python.org/archives/list/security-announce@python.org/thre…advisory, Vendor advisory
    • github.compython/cpython/commit/16c40f944b7bff724a403cf4902763d095bb4b2afix, Patch
    • github.compython/cpython/commit/9e863fab283eddca9c2a8f9d1ee30f4dc243e314fix, Patch
    • github.compython/cpython/commit/a86de0bc236fbb9452f98998fc8437e9fca35700fix, Patch
    • github.compython/cpython/commit/b93d6d3399adbd3a5037b6b92fc3587c85ac5d56fix, Patch
    • github.compython/cpython/commit/03ab7b44788bfd6b8927e16bcdbd025aa08dce06Patch
    • openwall.comlists/oss-security/2026/06/16/8
    • github.compython/cpython/commit/872038377db2e170e0e140b5f8aaedf636b3fbf5fix, Patch
    • NVD (NIST)vuln/detail/CVE-2026-12003web

    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 the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/python/cpython/commit/872038377db2e170e0e140b5f8aaedf636b3fbf5

      Source identifier: cna@python.org

    2. Record modifiedpython.org

      1 individual change: Affected versions (publisher)

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)changed
      CPython
      CPython

      Source identifier: cna@python.org

    3. Record modifiedpython.org

      1 individual change: Affected versions (publisher)

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)changed
      CPython
      CPython

      Source identifier: cna@python.org

    4. Receivedpython.org

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

      Weakness type: CWE-427

      Description added or changed

      Show 6 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      To allow builds of Python to be run from an in-tree layout (rather than an installed file layout), the VPATH variable is defined at build time and used to locate certain landmarks - specifically, Modules/setup.local. When this landmark is found relative to VPATH relative to the executable, Python assumes it is running in a source tree and generates a different default sys.path. This code remains in release builds, so that release-ready builds can be built in-tree. On Windows, since builds are written to 'PCbuild/', the value of VPATH is set to '..\..', which results in a landmark of '..\..\Modules\setup.local'. This path is outside the install directory of Python, and may have different permissions, potentially allowing a low-privilege user to create the landmark and an alternative `Lib` folder that will be discovered by an otherwise restricted install. Such a setup occurs with the legacy default install location for all users (in the now superseded EXE installer), due to how Windows allows all users to create folders in the root directory of their OS drive. Our recommended mitigation on Windows is to migrate away from the legacy installer and use the new [Python install manager](https://www.python.org/downloads/latest/pymanager/) to install for the current user. Installs where the directory two levels above the Python installation directory have equivalent permissions are unaffected (in general, a per-user install cannot be modified at all by other users, removing any escalation of privilege risk, and could be directly modified by a privileged user, making the potential tampering irrelevant). Alternative mitigations might include preemptively creating and restricting access to a `Modules` directory. Be aware that only 3.13 and 3.14 will receive updated legacy installers - earlier fixes are only provided as sources. Platforms other than Windows allow VPATH to be overridden, but as they don't usually use a separated directory in the build for binaries, are unlikely to have a landmark reference outside of the install directory. The landmark detection involving VPATH is a fallback for when a more specific landmark - .\pybuilddir.txt - is absent, and was included for compatibility. Future releases of Python will no longer include the fallback, and so builds will need to generate or preserve the pybuilddir.txt file in order to work in-tree. This landmark file has been generated on Windows since 3.11, and on other platforms for longer.
      CVSSadded
      —
      AV:L/AC:L/AT:P/PR:L/UI:A/VC:H/VI:H/VA:N/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-427
      Referenceadded
      —
      https://github.com/python/cpython/issues/151544
      Referenceadded
      —
      https://github.com/python/cpython/pull/151545
      Referenceadded
      —
      https://https://mail.python.org/archives/list/security-announce@python.org/thread/JIFOBO7UX3LY4VJKJUOKYJV62CFR2IRH/

      Source identifier: cna@python.org

    One NVD translation into another language is hidden.

    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-2026-12003
    <a href="https://intel.neosec.eu/en/cve/CVE-2026-12003"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-12003.svg?lang=en" alt="CVE-2026-12003 – NEOSEC Intel" height="20"></a>