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    CVE-2026-84642

    The values of the mail.allowed_attachment_hostnames advanced config setting were used in a regular expression without escaping. For some possible valid hostnames, this could allow certain unintended hostnames to also match and serve remote attachments. This vulnerability was fixed in Thunderbird 155 and Thunderbird 153.2.

    Published:Sep 1, 2026
    Last Modified:Sep 3, 2026
    EPS:Sep 1, 2026
    EPSS Score:0.00271
    CVSS Score:7.5

    Affected Products

    Vendor
    Mozilla
    Product
    Thunderbird

    Exploits

    No exploit reference

    Common Attack Pattern Enumeration and Classification (CAPEC)

    CAPEC-492 Regular Expression Exponential Blowup

    Related CVEs

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    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…
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    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