HighCVE-2026-124853

    Mozilla Firefox und Thunderbird: Mehrere Schwachstellen

    Published Sources: BSI

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    What is affected, what to do

    Sandbox escape due to incorrect boundary conditions in the Graphics: Text component. This vulnerability was fixed in Firefox 160, Firefox ESR 115.45, Firefox ESR 153.7, Thunderbird 160, and Thunderbird 153.7.

    Update Firefox to version 160, Firefox ESR to version 115.45, Thunderbird to version 153.7.

    Affected
    • Debian Firefox-esr 153.7.0esr-1~deb12u1..*
    • Debian Firefox-esr 153.7.0esr-1~deb13u1..*
    • Debian Thunderbird 1:153.7.0esr-1~deb13u1..*
    • Debian Thunderbird 1:153.7.0esr-1~deb12u1..*

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

    Metrics

    9.6

    XIEM Effective CVSS

    Highest available CVSS rating from NVD and vendor data.

    Source: Vendor (CNA), CVSS v3

    9.6

    CVSS v3

    Severity Critical on the scale from 0 to 10.

    Source: BSI

    0.4 %

    EPSS score

    Low — model estimates < 1% exploitation likelihood.

    Source: FIRST EPSS, percentile 35.6

    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
    79.53 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
    9.6 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
    9.6
    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
    35.6
    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: total
    Source: CISA Vulnrichment, as of 10 November 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-119

    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

    Sandbox escape due to incorrect boundary conditions in the Graphics: Text component. This vulnerability was fixed in Firefox 160, Firefox ESR 115.45, Firefox ESR 153.7, Thunderbird 160, and Thunderbird 153.7.

    Source: BSI WID Portal

    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
    MozillaFirefox
    • < 160
    • 160
    MozillaFirefox ESR
    • < 115.45
    • < 153.7
    • 115.45
    • 153.7
    MozillaThunderbird
    • < 153.7
    • < 160
    • 153.7
    • 160
    From bundled advisories, not CVE-specific (5)

    Product list of a bundled advisory that does not state which product this CVE affects.

    Products from bundled advisories
    Affected versionsFixed in
    MozillaFirefox
    • < 158
    • 158
    MozillaFirefox ESR
    • < 115.43
    • < 153.5
    • 115.43
    • 153.5
    MozillaThunderbird
    • < 153.5
    • < 158
    • 153.5
    • 158

    Vendors and products

    Affected operating systems

    Affected operating systems
    Linuxdebianfirefox-esrbookworm
    Linuxdebianfirefox-esrtrixie
    Linuxdebianthunderbirdbookworm
    Linuxdebianthunderbirdtrixie

    Weakness classes (CWE)

    • CWE-119Improper Restriction of Operations within the Bounds of a Memory Buffer

      Class

      The product performs operations on a memory buffer, but it reads from or writes to a memory location outside the buffer's intended boundary. This may result in read or write operations on unexpected memory locations that could be linked to other variables, data structures, or internal program data.

      Entry at MITRE CWE-119

    References & sources

    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 modifiedCISA ADP

      Weakness type: CWE-119

      Show the original change
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Weakness type (CWE)added
      —
      CWE-119

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

    2. Record modifiedMozilla

      Description added or changed

      Show 3 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionchanged
      Sandbox escape due to incorrect boundary conditions in the Graphics: Text component. This vulnerability was fixed in Firefox 160, Firefox ESR 115.45, Firefox ESR 153.7, and Thunderbird 160.
      Sandbox escape due to incorrect boundary conditions in the Graphics: Text component. This vulnerability was fixed in Firefox 160, Firefox ESR 115.45, Firefox ESR 153.7, Thunderbird 160, and Thunderbird 153.7.
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/124xxx/CVE-2026-124853.json">CVE-2026-124853</a>
      Referenceadded
      —
      https://www.mozilla.org/security/advisories/mfsa2026-129/

      Source identifier: security@mozilla.org

    3. Record modifiedMozilla

      Description added or changed

      Show 3 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionchanged
      Sandbox escape due to incorrect boundary conditions in the Graphics: Text component. This vulnerability was fixed in Firefox 160, Firefox ESR 115.45, and Firefox ESR 153.7.
      Sandbox escape due to incorrect boundary conditions in the Graphics: Text component. This vulnerability was fixed in Firefox 160, Firefox ESR 115.45, Firefox ESR 153.7, and Thunderbird 160.
      Affected versions (publisher)added
      —
      Affected value modified. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/124xxx/CVE-2026-124853.json">CVE-2026-124853</a>
      Referenceadded
      —
      https://www.mozilla.org/security/advisories/mfsa2026-128/

      Source identifier: security@mozilla.org

    4. Record modifiedCISA ADP

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

      CISA assessment (SSVC): exploitation: none known, automatable: no

      Show 2 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      CVSSadded
      —
      AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H
      SSVC assessmentadded
      —
      {"id":"CVE-2026-124853","role":"CISA Coordinator","options":[{"exploitation":"none"},{"automatable":"no"},{"technicalImpact":"total"}],"version":"2.0.3","timestamp":"2026-11-10T14:40:48.444928Z"}

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

    5. ReceivedMozilla

      Description added or changed

      Show 6 original changes
      Individual changes of this event as published by NVD
      TypeActionBeforeAfter
      Descriptionadded
      —
      Sandbox escape due to incorrect boundary conditions in the Graphics: Text component. This vulnerability was fixed in Firefox 160, Firefox ESR 115.45, and Firefox ESR 153.7.
      Affected versions (publisher)added
      —
      New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/124xxx/CVE-2026-124853.json">CVE-2026-124853</a>
      Referenceadded
      —
      https://bugzilla.mozilla.org/show_bug.cgi?id=2058035
      Referenceadded
      —
      https://www.mozilla.org/security/advisories/mfsa2026-125/
      Referenceadded
      —
      https://www.mozilla.org/security/advisories/mfsa2026-126/
      Referenceadded
      —
      https://www.mozilla.org/security/advisories/mfsa2026-127/

      Source identifier: security@mozilla.org

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    <a href="https://intel.neosec.eu/en/cve/CVE-2026-124853"><img src="https://intel.neosec.eu/badge/cve/CVE-2026-124853.svg?lang=en" alt="CVE-2026-124853 – NEOSEC Intel" height="20"></a>