HighCVE-2026-9669

    bz2.BZ2Decompressor reuse after error can cause a stack buffer overflow (CVE-2026-9669)

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

    What is affected, what to do

    bz2.BZ2Decompressor objects could be reused after a decompression error. If an application caught the resulting OSError and retried with the same decompressor, crafted input could cause the decompressor to resume from an invalid internal state and perform out-of-bounds writes to a stack buffer.

    Update Python Software Foundation CPython to version 3.10.21, Python Software Foundation CPython to version 3.11.16, Python Software Foundation CPython to version 3.12.14.

    Affected
    • Python Software Foundation CPython lt *..3.10.21
    • Python Software Foundation CPython lt 3.11.0..3.11.16
    • Python Software Foundation CPython lt 3.12.0..3.12.14
    • Python Software Foundation CPython lt 3.13.0..3.13.14
    • Python Software Foundation CPython lt 3.14.0..3.14.6
    • Python Software Foundation CPython lt 3.15.0a1..3.15.0b3
    Fixed in
    • Python Software Foundation CPython 3.10.21
    • Python Software Foundation CPython 3.11.16
    • Python Software Foundation CPython 3.12.14
    • Python Software Foundation CPython 3.13.14
    • Python Software Foundation CPython 3.14.6
    • Python Software Foundation CPython 3.15.0b3

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

    Metrics

    8.2

    Priority

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

    Source: NVD, CVSS v4

    8.2

    CVSS v4

    Severity High on the scale from 0 to 10.

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

    0.4 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 36.8

    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
    70.54 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
    8.2 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
    8.2
    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
    0.4 %
    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
    36.8
    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-121

    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

    bz2.BZ2Decompressor objects could be reused after a decompression error. If an application caught the resulting OSError and retried with the same decompressor, crafted input could cause the decompressor to resume from an invalid internal state and perform out-of-bounds writes to a stack buffer. This could crash the process when processing untrusted data.

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

    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
    • 3.11.0 – < 3.11.16
    • 3.15.0a1 – < 3.15.0b3
    • 3.14.0 – < 3.14.6
    • 3.13.0 – < 3.13.14
    • < 3.10.21
    • 3.12.14
    • 3.11.16
    • 3.15.0b3
    • 3.14.6
    • 3.13.14
    • 3.10.21
    Open SourcePython CPython
    • < 3.16.0
    • 3.16.0
    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
    Linuxdebianpython3.11bookworm

    Weakness classes (CWE)

    • CWE-121Stack-based Buffer Overflow

      Variant

      A stack-based buffer overflow condition is a condition where the buffer being overwritten is allocated on the stack (i.e., is a local variable or, rarely, a parameter to a function).

      Entry at MITRE CWE-121

    References & sources

    • github.compython/cpython/pull/150600web, Patch
    • mail.python.orgarchives/list/security-announce@python.org/thread/DBJZETMGUIFK7…advisory, Vendor advisory
    • github.compython/cpython/issues/150599report, Issue tracking
    • github.compython/cpython/commit/157a5df8cb5d82b33f918a7489e72ce95ceb12b6fix, Patch
    • github.compython/cpython/commit/5755d0f083949ff3c5bf3a37e673e24e306b036efix, Patch
    • github.compython/cpython/commit/619a12b2e545391dc436b3af79dda22337382a6ffix, Patch
    • github.compython/cpython/commit/d3ca26983dfbccdf609f24ff5877dc3118e4702dfix, Patch
    • github.compython/cpython/commit/938ec030e90c5e53f1faac6fab1643f14e4f4a79fix, Patch
    • github.compython/cpython/commit/991e6cf86496718c4ef00b362d640e00cb5c85b2Patch
    • openwall.comlists/oss-security/2026/06/08/17
    • github.compython/cpython/commit/1ba6135eae75ad8413413caeeedb56ae72320636fix, Patch
    • NVD (NIST)vuln/detail/CVE-2026-9669web

    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/1ba6135eae75ad8413413caeeedb56ae72320636

      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

      Show 4 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Referenceadded
      —
      https://github.com/python/cpython/commit/157a5df8cb5d82b33f918a7489e72ce95ceb12b6
      Referenceadded
      —
      https://github.com/python/cpython/commit/5755d0f083949ff3c5bf3a37e673e24e306b036e
      Referenceadded
      —
      https://github.com/python/cpython/commit/619a12b2e545391dc436b3af79dda22337382a6f
      Referenceadded
      —
      https://github.com/python/cpython/commit/d3ca26983dfbccdf609f24ff5877dc3118e4702d

      Source identifier: cna@python.org

    4. 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/2026/06/08/17

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

    5. Receivedpython.org

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

      Weakness type: CWE-121

      Description added or changed

      Show 6 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      bz2.BZ2Decompressor objects could be reused after a decompression error. If an application caught the resulting OSError and retried with the same decompressor, crafted input could cause the decompressor to resume from an invalid internal state and perform out-of-bounds writes to a stack buffer. This could crash the process when processing untrusted data.
      CVSSadded
      —
      AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/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-121
      Referenceadded
      —
      https://github.com/python/cpython/issues/150599
      Referenceadded
      —
      https://github.com/python/cpython/pull/150600
      Referenceadded
      —
      https://mail.python.org/archives/list/security-announce@python.org/thread/DBJZETMGUIFK7DVUWMOXHD3Z6IX2QPSX/

      Source identifier: cna@python.org

    One NVD translation into another language is hidden.

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