HighCVE-2026-49825

    lxml: javascript: URL bypass in Cleaner via xlink:href (CVE-2026-49825)

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

    What is affected, what to do

    A flaw was found in lxml, a library for processing XML and HTML in Python. The `lxml.html.defs.link_attrs` were missing `xlink:href`, which could allow an attacker to bypass URL filtering mechanisms.

    Update lxml to version 6.1.1, Fedora-python Lxml Html Clean to version 0.4.5.

    Affected
    • lxml lt *..6.1.1
    • Fedora-python Lxml Html Clean lt *..0.4.5
    Fixed in
    • lxml 6.1.1
    • Fedora-python Lxml Html Clean 0.4.5

    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: Vendor (CNA), CVSS v3

    8.2

    CVSS v3

    Severity High on the scale from 0 to 10.

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

    0.3 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 22.4

    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
    68.82 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 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
    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
    0.3 %
    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
    22.4
    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: proof of concept · not automatable · Technical impact: partial
    Source: CISA Vulnrichment, as of 21 August 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-79, CWE-184

    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

    A flaw was found in lxml, a library for processing XML and HTML in Python. The `lxml.html.defs.link_attrs` were missing `xlink:href`, which could allow an attacker to bypass URL filtering mechanisms. This vulnerability enables URL bypass attacks in embedded content such as Scalable Vector Graphics (SVG) or Mathematical Markup Language (MathML), potentially leading to information disclosure or arbitrary code execution in the context of the user's browser.

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

    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
    fedora-pythonlxml_html_clean
    • < 0.4.5
    • 0.4.5
    lxmllxml
    • < 6.1.1
    • 6.1.1
    Red HatAnsible Automation Platform
    • 2.7
    • 2.4
    • —
    • —
    Red HatEnterprise Linux
    • 9
    • —

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianlxmlbookworm
    Linuxubuntulxmlbionic
    Linuxubuntulxmlfocal
    Linuxubuntulxmljammy
    Linuxubuntulxmlnoble
    Linuxubuntulxmlresolute
    Linuxubuntulxmltrusty
    Linuxubuntulxmlxenial

    Weakness classes (CWE)

    • CWE-79Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

      Base

      The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users.

      Entry at MITRE CWE-79

    • CWE-184Incomplete List of Disallowed Inputs

      Base

      The product implements a protection mechanism that relies on a list of inputs (or properties of inputs) that are not allowed by policy or otherwise require other action to neutralize before additional processing takes place, but the list is incomplete.

      Entry at MITRE CWE-184

    References & sources

    • github.comfedora-python/lxml_html_clean/security/advisories/GHSA-4jhm-jv6…web, x_refsource_CONFIRM
    • github.comfedora-python/lxml_html_cleanpackage
    • pypi.orgproject/lxml-html-cleanpackage
    • GitHub Security Advisoriesadvisories/GHSA-4jhm-jv67-739fadvisory
    • NVD (NIST)vuln/detail/CVE-2026-49825advisory
    • github.comfedora-python/lxml_html_clean/commit/322357ac61c6cf80fcbaba53b4…x_refsource_MISC
    • github.comlxml/lxml/commit/5927a6d5e851845140975d99b65461e255caaab0x_refsource_MISC
    • github.comfedora-python/lxml_html_clean/releases/tag/0.4.5x_refsource_MISC
    • github.comlxml/lxml/releases/tag/lxml-6.1.1x_refsource_MISC

    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. ReceivedGitHub

      CVSS V3.1: AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N

      Weakness type: CWE-79, CWE-184

      Description added or changed

      Show 10 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Affected versions (publisher)added
      —
      lxml, lxml_html_clean
      Descriptionadded
      —
      lxml is a library for processing XML and HTML in the Python language. Prior to 6.1.1, link attributes in ``lxml.html.defs.link_attrs`` were missing ``xlink:href``, which can be used for URL bypass attacks in embedded SVG/MathML/etc. content. This vulnerability was fixed in lxml 6.1.1 and lxml_html_clean 0.4.5.
      CVSSadded
      —
      AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:L/A:N
      Weakness type (CWE)added
      —
      CWE-79
      Weakness type (CWE)added
      —
      CWE-184
      Referenceadded
      —
      https://github.com/fedora-python/lxml_html_clean/commit/322357ac61c6cf80fcbaba53b4e92e31f3ded9f2
      Referenceadded
      —
      https://github.com/fedora-python/lxml_html_clean/releases/tag/0.4.5
      Referenceadded
      —
      https://github.com/fedora-python/lxml_html_clean/security/advisories/GHSA-4jhm-jv67-739f
      Referenceadded
      —
      https://github.com/lxml/lxml/commit/5927a6d5e851845140975d99b65461e255caaab0
      Referenceadded
      —
      https://github.com/lxml/lxml/releases/tag/lxml-6.1.1

      Source identifier: security-advisories@github.com

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