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Thunderbird Security Update — AlmaLinux 9 (ALSA-2026:93443)

ALSA-2026:93443 updates Thunderbird on AlmaLinux 9 with a large Mozilla security batch — roughly 60 CVEs (CVE-2026-45186 libexpat DoS, CVE-2026-109764 Enterprise Policies mitigation bypass, DOM spoofing issues and more), aggregate CVSS 2.9. The low score reflects mostly moderate individual flaws, but mail clients render untrusted content by definition: update with dnf update thunderbird and restart the client.

High 2.9 CVSS
AlmaLinux 9

What this means under a SharedLicense license

Thunderbird renders attacker-controlled email content — the fixed spoofing and engine flaws are the standard malicious-email attack surface, and the mitigation bypass weakens defenses enterprises rely on for policy enforcement.

Mozilla Thunderbird is a standalone mail and newsgroup client.  

Security Fix(es):  

  * libexpat: denial of service via crafted XML input (CVE-2026-45186)
  * firefox: Mitigation bypass in the Enterprise Policies component (CVE-2026-109764)
  * firefox: Spoofing issue in the DOM: Web Serial component (CVE-2026-109770)
  * firefox: Mitigation bypass in the File Handling component (CVE-2026-109783)
  * firefox: thunderbird: Privilege escalation in the Application Update component (CVE-2026-109704)
  * firefox: Use-after-free in the XML component (CVE-2026-109718)
  * firefox: Information disclosure in the PDF Viewer component (CVE-2026-109742)
  * firefox: Incorrect boundary conditions in the JavaScript Engine component (CVE-2026-109715)
  * firefox: firefox: Sandbox escape via incorrect boundary conditions in Win32 widget (CVE-2026-109740)
  * firefox: Use-after-free in the Storage: IndexedDB component (CVE-2026-109706)
  * firefox: Use-after-free in the Crash Reporting component (CVE-2026-109713)
  * firefox: Use-after-free in the DOM: Core & HTML component (CVE-2026-109724)
  * firefox: Sandbox escape due to uninitialized memory in the DOM: Web Serial component (CVE-2026-109745)
  * firefox: Mitigation bypass in the File Handling component (CVE-2026-109782)
  * firefox: Information disclosure, privilege escalation in the Security: Process Sandboxing component (CVE-2026-109709)
  * firefox: Sandbox escape, site isolation issue due to incorrect boundary conditions, use-after-free in the Networking component (CVE-2026-109705)
  * firefox: Use-after-free in the Audio/Video: Playback component (CVE-2026-109738)
  * firefox: Sandbox escape due to race condition in the Networking component (CVE-2026-109757)
  * firefox: Use-after-free in the Storage: Bucket File System component (CVE-2026-109741)
  * firefox: Use-after-free in the JavaScript Engine: JIT component (CVE-2026-109729)
  * firefox: Other issue in the DOM: File component (CVE-2026-109744)
  * firefox: Incorrect boundary conditions in the JavaScript Engine component (CVE-2026-109716)
  * firefox: Race condition, use-after-free in the Graphics: CanvasWebGL component (CVE-2026-109719)
  * firefox: Incorrect boundary conditions in the Layout component (CVE-2026-109753)
  * firefox: Integer overflow in the Layout: Text and Fonts component (CVE-2026-109723)
  * firefox: Privilege escalation in the DOM: Navigation component (CVE-2026-109756)
  * firefox: JIT miscompilation in the JavaScript Engine: JIT component (CVE-2026-109733)
  * firefox: thunderbird: Mitigation bypass in the DOM: Security component (CVE-2026-109734)
  * firefox: Mitigation bypass in the File Handling component (CVE-2026-109763)
  * firefox: Sandbox escape due to incorrect boundary conditions in the Networking component (CVE-2026-109708)
  * firefox: Use-after-free in the DOM: Bindings (WebIDL) component (CVE-2026-109717)
  * firefox: Use-after-free in the DOM: Workers component (CVE-2026-109752)
  * firefox: Race condition in the XPCOM component (CVE-2026-109776)
  * firefox: Sandbox escape due to use-after-free in the Networking component (CVE-2026-109707)
  * firefox: Mitigation bypass in the Networking: HTTP component (CVE-2026-109760)
  * firefox: JIT miscompilation in the JavaScript: WebAssembly component (CVE-2026-109720)
  * firefox: Information disclosure in the Storage: IndexedDB component (CVE-2026-109777)
  * firefox: Use-after-free in the SVG component (CVE-2026-109726)
  * firefox: Integer overflow in the Graphics component (CVE-2026-109730)
  * firefox: Use-after-free in the Audio/Video component (CVE-2026-109727)
  * firefox: Mitigation bypass in the Enterprise Policies component (CVE-2026-109737)
  * firefox: Mitigation bypass in the Enterprise Policies component (CVE-2026-109766)
  * firefox: Use-after-free in the DOM: Streams component (CVE-2026-109732)
  * firefox: Site isolation issue in the Networking component (CVE-2026-109759)
  * firefox: Privilege escalation in the WebExtensions component (CVE-2026-109778)
  * firefox: Incorrect boundary conditions in the SVG component (CVE-2026-109762)
  * firefox: Race condition, use-after-free in the Graphics: Text component (CVE-2026-109765)
  * firefox: Incorrect boundary conditions in the DOM: Editor component (CVE-2026-109754)
  * firefox: Information disclosure in the Networking component (CVE-2026-109751)
  * firefox: Use-after-free in the DOM: Core & HTML component (CVE-2026-109725)
  * firefox: Sandbox escape due to uninitialized memory in the Graphics component (CVE-2026-109712)
  * firefox: Use-after-free in the Graphics: Canvas2D component (CVE-2026-109711)
  * firefox: Frame poisoning in the Layout component (CVE-2026-109736)
  * firefox: JIT miscompilation in the JavaScript Engine: JIT component (CVE-2026-109722)
  * firefox: Information disclosure in the Networking component (CVE-2026-109767)
  * firefox: Denial-of-service in the WebRTC component (CVE-2026-109775)
  * firefox: Use-after-free in the DOM: Animation component (CVE-2026-109728)
  * firefox: Denial-of-service in the Printing: Output component (CVE-2026-109781)
  * firefox: thunderbird: Use-after-free in the Graphics: Text component (CVE-2026-109710)
  * firefox: thunderbird: Incorrect boundary conditions in the Graphics: Canvas2D component (CVE-2026-109731)
  * firefox: Incorrect boundary conditions in the JavaScript Engine: JIT component (CVE-2026-109721)
  * firefox: Privilege escalation in the Panning and Zooming component (CVE-2026-109743)


Bug Fix(es) and Enhancement(s):  

  * Thunderbird ESR 153 rebase [rhel-9.8.z] (JIRA:RHEL-175199)


For more details about the security issue(s), including the impact, a CVSS score, acknowledgments, and other related information, refer to the CVE page(s) listed in the References section.

Frequently Asked Questions

What is ALSA-2026:93443?
It is AlmaLinux's Thunderbird erratum for AlmaLinux 9, applying a large Mozilla security batch — roughly 60 CVEs including CVE-2026-45186 (libexpat denial of service via crafted XML), CVE-2026-109764 (Enterprise Policies mitigation bypass) and multiple DOM spoofing issues.
Who is affected?
AlmaLinux 9 desktops and workstations running Thunderbird — the flaws trigger on rendering malicious email content, so every mail client user is in scope.
How do I apply the fix?
Run dnf update thunderbird and restart the client; verify the updated version in its About dialog.
Why is the aggregate CVSS only 2.9 for so many CVEs?
The aggregate reflects the individually moderate ratings of most items in the batch — but spoofing and mitigation-bypass flaws aid real phishing attacks, so the update belongs in the regular patch cycle regardless of the low number.

References

Security Advisories

Related Advisories

Kernel Security Update — AlmaLinux 9 (ALSA-2026:93412)

2026-11-09

Fence-Agents Security Update — AlmaLinux 9 (ALSA-2026:94500)

2026-11-04

Cockpit Security Update — AlmaLinux 9 (ALSA-2026:94533)

2026-11-04

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