MediumCVE-2026-6019

    BaseCookie.js_output() does not neutralize embedded characters (CVE-2026-6019)

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

    What is affected, what to do

    http.cookies.Morsel.js_output() returns an inline <script> snippet and only escapes " for JavaScript string context. It does not neutralize the HTML parser-sensitive sequence </script> inside the generated script element.

    An exploit is publicly available. Update Python Software Foundation CPython to version 3.13.14, Python Software Foundation CPython to version 3.14.5rc1, Python Software Foundation CPython to version 3.15.0b1.

    Affected
    • Python Software Foundation CPython lt *..3.13.14
    • Python Software Foundation CPython lt 3.14.0a1..3.14.5rc1
    • Python Software Foundation CPython lt 3.15.0a1..3.15.0b1
    Fixed in
    • Python Software Foundation CPython 3.13.14
    • Python Software Foundation CPython 3.14.5rc1
    • Python Software Foundation CPython 3.15.0b1

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

    Metrics

    6.1

    Priority

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

    Source: NVD, CVSS v3

    6.1

    CVSS v3

    Severity Medium on the scale from 0 to 10.

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

    0.2 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 11.3

    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
    48.06 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
    PoC (publicly reported)
    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
    6.1 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
    6.1
    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
    2.1
    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
    0.2 %
    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
    11.3
    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
    CISA assessment (SSVC)
    Exploitation: none known · not automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 22 April 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-150, CWE-116

    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

    http.cookies.Morsel.js_output() returns an inline <script> snippet and only escapes " for JavaScript string context. It does not neutralize the HTML parser-sensitive sequence </script> inside the generated script element. Mitigation base64-encodes the cookie value to disallow escaping using cookie value.

    Source: suse_csaf, Ubuntu Security Notices, Debian LTS Advisories, BSI WID Portal, BSI CSAF, NVD (NIST), Microsoft Security Update Guide, OSV (Open Source Vulnerabilities), redhat_csaf, cvelistv5, ENISA EUVD, 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
    • 3.15.0a1 – < 3.15.0b1
    • 3.14.0a1 – < 3.14.5rc1
    • < 3.13.14
    • 3.15.0b1
    • 3.14.5rc1
    • 3.13.14
    pythonpython
    • < 3.13.14
    • 3.15.0
    • 3.14.0 – ≤ 3.14.4
    • 3.13.14
    • —
    • —
    OracleSolaris
    • <11.3 ESU 36.36
    • <11.4 SRU 94
    • —
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxubuntupython2.7bionic
    Linuxubuntupython2.7focal
    Linuxubuntupython2.7jammy
    Linuxubuntupython2.7trusty
    Linuxubuntupython2.7xenial
    Linuxubuntupython3.10jammy
    Linuxdebianpython3.11bookworm
    Linuxubuntupython3.11jammy
    Linuxubuntupython3.12noble
    Linuxubuntupython3.14resolute
    Linuxubuntupython3.4trusty
    Linuxubuntupython3.5trusty
    Linuxubuntupython3.5xenial
    Linuxubuntupython3.6bionic
    Linuxubuntupython3.7bionic
    Linuxubuntupython3.8bionic
    Linuxubuntupython3.8focal
    Linuxubuntupython3.9focal

    Weakness classes (CWE)

    • CWE-150Improper Neutralization of Escape, Meta, or Control Sequences

      Variant

      The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as escape, meta, or control character sequences when they are sent to a downstream component.

      Entry at MITRE CWE-150

    • CWE-116Improper Encoding or Escaping of Output

      Class

      The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.

      Entry at MITRE CWE-116

    Public exploit references

    Publicly reported proof-of-concepts, exploit modules and detection templates for this vulnerability. NEOSEC links to the original sources only and does not provide any exploit code.

    Public exploit references
    Reference tagged as exploitgithub.com (opens in a new tab)PoC (publicly reported)reported, not verified—

    References & sources

    • github.compython/cpython/pull/148848web, Patch, Issue tracking, Patch
    • github.compython/cpython/issues/90309report, Issue tracking, Exploit, Issue tracking
    • mail.python.orgarchives/list/security-announce@python.org/thread/IVNWGV2BBNC3R…advisory, Vendor advisory, Mailing list, Vendor advisory
    • github.compython/cpython/commit/76b3923d688c0efc580658476c5f525ec8735104fix, Patch, Patch
    • github.compython/cpython/commit/3c59b8b53fc75c7f9578d16fb8201ceb43e8f76cfix, Patch, Patch
    • github.compython/cpython/commit/f795e042043dfe26c42e1971d4502c1cdc4c65b8fix, Patch, Patch
    • NVD (NIST)vuln/detail/CVE-2026-6019web

    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. NVD analysis modifiedNVD

      Product mapping changed:
      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Product configurationchanged
      OR *cpe:2.3:a:python:python:*:*:*:*:*:*:*:* versions up to (excluding) 3.15.0
      OR *cpe:2.3:a:python:python:3.15.0:alpha1:*:*:*:*:*:* *cpe:2.3:a:python:python:3.15.0:alpha2:*:*:*:*:*:* *cpe:2.3:a:python:python:3.15.0:alpha3:*:*:*:*:*:* *cpe:2.3:a:python:python:3.15.0:alpha4:*:*:*:*:*:* *cpe:2.3:a:python:python:3.15.0:alpha5:*:*:*:*:*:* *cpe:2.3:a:python:python:3.15.0:alpha6:*:*:*:*:*:* *cpe:2.3:a:python:python:3.15.0:alpha7:*:*:*:*:*:* *cpe:2.3:a:python:python:3.15.0:alpha8:*:*:*:*:*:* *cpe:2.3:a:python:python:*:*:*:*:*:*:*:* versions up to (excluding) 3.13.14 *cpe:2.3:a:python:python:*:*:*:*:*:*:*:* versions from (including) 3.14.0 up to (including) 3.14.4

      Source identifier: nvd@nist.gov

    One NVD translation into another language is hidden.

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    Badge preview for CVE-2026-6019
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