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Critical DSA-5950-1 4 CVEs

firefox-esr - security update

Published Jun 25, 2025 · Updated Mar 9, 2026

Fixed packages 1

ReleasePackageFixed in
Debian · 12 firefox-esr 128.12.0esr-1~deb12u1

Vulnerabilities 4

  • Critical 9.8

    Use-after-free in FontFaceSet

    A use-after-free in FontFaceSet resulted in a potentially exploitable crash. This vulnerability was fixed in Firefox 140, Firefox ESR 115.25, Firefox ESR 128.12, Thunderbird 140, and Thunderbird 128.12.

  • Medium 6.5

    Incorrect parsing of URLs could have allowed embedding of youtube.com

    Firefox could have incorrectly parsed a URL and rewritten it to the youtube.com domain when parsing the URL specified in an `embed` tag. This could have bypassed website security checks that restricted which domains users were allowed to embed. This vulnerabi…

  • Medium 6.1

    Content-Disposition header ignored when a file is included in an embed or object tag

    When a file download is specified via the `Content-Disposition` header, that directive would be ignored if the file was included via a `<embed>` or `<object>` tag, potentially making a website vulnerable to a cross-site scripting attack. This vuln…

  • Medium 4.3

    The WebCompat WebExtension shipped with Firefox exposed a persistent UUID

    An attacker who enumerated resources from the WebCompat extension could have obtained a persistent UUID that identified the browser, and persisted between containers and normal/private browsing mode, but not profiles. This vulnerability was fixed in Firefox 1…