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    CVE-2026-0891

    Memory safety bugs present in Firefox ESR 140.6, Thunderbird ESR 140.6, Firefox 146 and Thunderbird 146. Some of these bugs showed evidence of memory corruption and we presume that with enough effort some of these could have been exploited to run arbitrary code. This vulnerability was fixed in Firefox 147, Firefox ESR 140.7, Thunderbird 147, and Thunderbird 140.7.

    Published:Jan 13, 2026
    Last Modified:Apr 15, 2026
    EPS:Jan 13, 2026
    EPSS Score:0.00025
    CVSS Score:8.1

    Affected Products

    Vendor
    Mozilla
    Product
    Firefox
    Vendor
    Mozilla
    Product
    Firefox Esr
    Vendor
    Mozilla
    Product
    Thunderbird
    Vendor
    Mozilla
    Product
    Thunderbird Esr

    Exploits

    No exploit reference

    Related CVEs

    CVE-2026-84144 (CVSS 7.5) — Internally found bugs present in Thunderbird 154 and Thunderbird ESR 153.1. Some of these bugs showed evidence…
    CVE-2026-84143 (CVSS 9.8) — Internally found bugs present in Thunderbird 154, Thunderbird ESR 153.1 and Thunderbird ESR 140.14. Some of th…
    CVE-2026-84142 (CVSS 9.8) — Internally found bugs present in Thunderbird 154. Some of these bugs showed evidence of memory corruption or a…
    CVE-2026-84141 (CVSS 9.8) — Integer overflow in the Graphics: ImageLib component. This vulnerability was fixed in Firefox 155, Firefox ESR…
    CVE-2026-84140 (CVSS 9.8) — Site isolation issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 155, Firefox ES…
    CVE-2026-84139 (CVSS 6.1) — Clickjacking issue in the DOM: Events component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.…
    CVE-2026-84138 (CVSS 6.5) — Denial-of-service in the PDF Viewer component. This vulnerability was fixed in Firefox 155 and Thunderbird 155…
    CVE-2026-84137 (CVSS 4.3) — Spoofing issue in the DOM: Core & HTML component. This vulnerability was fixed in Firefox 155, Firefox ESR 153…
    CVE-2026-84136 (CVSS 6.1) — Other issue in the DOM: Navigation component. This vulnerability was fixed in Firefox 155, Firefox ESR 153.2, …
    CVE-2026-84135 (CVSS 9.8) — Other issue in Firefox Focus for Android. This vulnerability was fixed in Firefox 155.…

    References

    https://bugzilla.mozilla.org/buglist.cgi?bug_id=1964722%2C2000981%2C2003100%2C2003278
    https://www.mozilla.org/security/advisories/mfsa2026-01/
    https://www.mozilla.org/security/advisories/mfsa2026-03/
    https://www.mozilla.org/security/advisories/mfsa2026-04/
    https://www.mozilla.org/security/advisories/mfsa2026-05/
    https://access.redhat.com/errata/RHSA-2026:0667
    https://access.redhat.com/errata/RHSA-2026:0694
    https://access.redhat.com/errata/RHSA-2026:0924
    https://access.redhat.com/errata/RHSA-2026:1320
    https://access.redhat.com/errata/RHSA-2026:1413
    https://access.redhat.com/errata/RHSA-2026:1414
    https://access.redhat.com/errata/RHSA-2026:1415
    https://access.redhat.com/errata/RHSA-2026:1461
    https://access.redhat.com/errata/RHSA-2026:1462
    https://access.redhat.com/errata/RHSA-2026:1471
    https://access.redhat.com/errata/RHSA-2026:1487
    https://access.redhat.com/errata/RHSA-2026:2041
    https://access.redhat.com/errata/RHSA-2026:2043
    https://access.redhat.com/errata/RHSA-2026:2044
    https://access.redhat.com/errata/RHSA-2026:2047
    https://access.redhat.com/errata/RHSA-2026:2069
    https://access.redhat.com/errata/RHSA-2026:2070
    https://access.redhat.com/errata/RHSA-2026:2073
    https://access.redhat.com/errata/RHSA-2026:2074
    https://access.redhat.com/errata/RHSA-2026:2220
    https://access.redhat.com/errata/RHSA-2026:2231
    https://access.redhat.com/errata/RHSA-2026:2271
    https://access.redhat.com/errata/RHSA-2026:2286
    https://access.redhat.com/security/cve/CVE-2026-0891
    https://bugzilla.redhat.com/show_bug.cgi?id=2428963
    https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-0891.json

    Common Vulnerability Scoring System

    Attack Vector
    Network
    Adjacent
    Local
    Physical
    Privileges Required
    None
    Low
    High
    User Interaction
    None
    Required
    Scope
    Unchanged
    Changed
    Confidentiality
    None
    Low
    High
    Integrity
    None
    Low
    High
    Availability
    None
    Low
    High