MediumCVE-2026-87910

    tarfile hardlink fallback ignores custom extraction filter rejection via None (CVE-2026-87910)

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

    What is affected, what to do

    When tarfile extracts a link on a system that doesn't support links, it falls back to extracting a member from the archive. In this case, the filter function is run twice: once for the extracted member, and once with name set to the location of the link.

    Update Python Software Foundation CPython to version 3.10.22, Python Software Foundation CPython to version 3.11.17, Python Software Foundation CPython to version 3.12.15.

    Affected
    • Python Software Foundation CPython lt *..3.10.22
    • Python Software Foundation CPython lt 3.11.0..3.11.17
    • Python Software Foundation CPython lt 3.12.0..3.12.15
    • Python Software Foundation CPython lt 3.13.0..3.13.16
    • Python Software Foundation CPython lt 3.15.0a1..3.15.0rc3
    Fixed in
    • Python Software Foundation CPython 3.10.22
    • Python Software Foundation CPython 3.11.17
    • Python Software Foundation CPython 3.12.15
    • Python Software Foundation CPython 3.13.16
    • Python Software Foundation CPython 3.15.0rc3

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

    Metrics

    5.7

    Priority

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

    Source: Vendor (CNA), CVSS v4

    5.7

    CVSS v4

    Severity Medium on the scale from 0 to 10.

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

    0.6 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 49.0

    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
    74.49 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
    5.7 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
    5.7
    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
    0.6 %
    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
    49.0
    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
    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-22, CWE-59

    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

    When tarfile extracts a link on a system that doesn't support links, it falls back to extracting a member from the archive. In this case, the filter function is run twice: once for the extracted member, and once with name set to the location of the link. For one of the calls, the return value was ignored. Instead, the member should be skipped if either call returns None.

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

    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
    • 3.15.0a1 – < 3.15.0rc3
    • 3.13.0 – < 3.13.16
    • 3.12.0 – < 3.12.15
    • 3.11.0 – < 3.11.17
    • < 3.10.22
    • 3.15.0rc3
    • 3.13.16
    • 3.12.15
    • 3.11.17
    • 3.10.22
    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

    Weakness classes (CWE)

    • CWE-22Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

      Base

      The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.

      Entry at MITRE CWE-22

    • CWE-59Improper Link Resolution Before File Access ('Link Following')

      Base

      The product attempts to access a file based on the filename, but it does not properly prevent that filename from identifying a link or shortcut that resolves to an unintended resource.

      Entry at MITRE CWE-59

    References & sources

    • mail.python.orgarchives/list/security-announce@python.org/thread/57TBTLL2W6APM…Vendor advisory
    • github.compython/cpython/pull/157266Patch
    • github.compython/cpython/issues/157265Issue tracking
    • openwall.comlists/oss-security/2026/09/11/8
    • github.compython/cpython/commit/d9565e54b1fc6d63c5be9afd58114499128fa57bfix, Patch
    • github.compython/cpython/commit/fb2f0bbc3b35264f09cc2cb2934b7987527a6bc2fix, Patch
    • NVD (NIST)vuln/detail/CVE-2026-87910web
    • github.compython/cpython/commit/9c17bace90f88dfba6d0e2fe23c8e7ae35f83955Patch
    • github.compython/cpython/commit/764fd0af8d9e19d3684a58d2e58bf770f0605036Patch
    • github.compython/cpython/commit/2eb0c2f1dc71847731b6ab30aebefd058d482a7ffix, Patch
    • github.compython/cpython/commit/c1f106d240c4ffcb3608ed0a20e8aba6c865f6d3fix, Patch
    • github.compython/cpython/commit/3105a3498aaf681ce128cf5baf83c2e5574267c5fix, Patch
    • github.compython/cpython/commit/a4919937a4e1e69a0d178909c6f20557eca5d1d0fix, Patch

    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

      1 individual change: Affected versions (publisher)

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/87xxx/CVE-2026-87910.json">CVE-2026-87910</a>

      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)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/87xxx/CVE-2026-87910.json">CVE-2026-87910</a>

      Source identifier: cna@python.org

    3. Record modifiedpython.org

      Show 3 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/87xxx/CVE-2026-87910.json">CVE-2026-87910</a>
      Referenceadded
      —
      https://github.com/python/cpython/commit/3105a3498aaf681ce128cf5baf83c2e5574267c5
      Referenceadded
      —
      https://github.com/python/cpython/commit/a4919937a4e1e69a0d178909c6f20557eca5d1d0

      Source identifier: cna@python.org

    4. 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)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/87xxx/CVE-2026-87910.json">CVE-2026-87910</a>

      Source identifier: cna@python.org

    5. Record modifiedpython.org

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/python/cpython/commit/2eb0c2f1dc71847731b6ab30aebefd058d482a7f
      Referenceadded
      —
      https://github.com/python/cpython/commit/c1f106d240c4ffcb3608ed0a20e8aba6c865f6d3

      Source identifier: cna@python.org

    Show 7 older changes

    1. 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)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/87xxx/CVE-2026-87910.json">CVE-2026-87910</a>

      Source identifier: cna@python.org

    2. Record modifiedpython.org

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/python/cpython/commit/764fd0af8d9e19d3684a58d2e58bf770f0605036

      Source identifier: cna@python.org

    3. Record modifiedpython.org

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/python/cpython/commit/9c17bace90f88dfba6d0e2fe23c8e7ae35f83955

      Source identifier: cna@python.org

    4. Record modifiedpython.org

      Show 3 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/87xxx/CVE-2026-87910.json">CVE-2026-87910</a>
      Referenceadded
      —
      https://github.com/python/cpython/commit/d9565e54b1fc6d63c5be9afd58114499128fa57b
      Referenceadded
      —
      https://github.com/python/cpython/commit/fb2f0bbc3b35264f09cc2cb2934b7987527a6bc2

      Source identifier: cna@python.org

    5. Record modifiedCVE Program

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      http://www.openwall.com/lists/oss-security/2026/09/11/8

      Source identifier: af854a3a-2127-422b-91ae-364da2661108

    6. 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 assessmentadded
      —
      {"id":"CVE-2026-87910","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"partial"}],"version":"2.0.3","timestamp":"2026-09-11T19:23:39.973519Z"}

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

    7. Receivedpython.org

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

      Weakness type: CWE-22, CWE-59

      Description added or changed

      Show 8 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      When tarfile extracts a link on a system that doesn't support links, it falls back to extracting a member from the archive. In this case, the filter function is run twice: once for the extracted member, and once with name set to the location of the link. For one of the calls, the return value was ignored. Instead, the member should be skipped if either call returns None.
      CVSSadded
      —
      AV:N/AC:L/AT:P/PR:L/UI:A/VC:N/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-22
      Weakness type (CWE)added
      —
      CWE-59
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/87xxx/CVE-2026-87910.json">CVE-2026-87910</a>
      Referenceadded
      —
      https://github.com/python/cpython/issues/157265
      Referenceadded
      —
      https://github.com/python/cpython/pull/157266
      Referenceadded
      —
      https://mail.python.org/archives/list/security-announce@python.org/thread/57TBTLL2W6APMZR3A25B2YV7GL3EPTDJ/

      Source identifier: cna@python.org

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