# Mozilla Firefox and Thunderbird patch critical code execution flaws

Published: 2026-06-09 · Severity: routine
Canonical: https://vorant.io/reports/11d2253b-9863-5360-a8de-520a2349ea8a/mozilla-firefox-and-thunderbird-patch-critical-code-execution-flaws

> Critical memory safety and privilege escalation vulnerabilities in Firefox and Thunderbird allow arbitrary code execution; no active exploitation reported.

Mozilla has released security updates addressing multiple vulnerabilities across Firefox, Firefox ESR, Thunderbird, and Thunderbird ESR. The most severe issues include memory safety bugs, privilege escalation in the Firefox Updater, WebGL shader memory corruption on macOS, and process isolation bypass via JavaScript. Successful exploitation could permit arbitrary code execution with the privileges of the affected user, potentially allowing installation of programs, data theft or modification, and unauthorized account creation.

Affected versions include Firefox prior to 138, Firefox ESR prior to 115.23 and 128.10, Thunderbird prior to 138, and Thunderbird ESR prior to 128.10. The advisory lists 13 distinct CVEs spanning memory safety issues, privilege escalation, information leakage, and local code execution. At the time of publication, no exploitation in the wild has been reported. Defenders should prioritize patching immediately, enforce least-privilege user accounts, and enable exploit-protection features on endpoints.

## Mentioned in this report

- Vulnerabilities: CVE-2025-2817, CVE-2025-4082, CVE-2025-4083, CVE-2025-4084, CVE-2025-4085, CVE-2025-4086, CVE-2025-4087, CVE-2025-4088, CVE-2025-4089, CVE-2025-4090, CVE-2025-4091, CVE-2025-4092, CVE-2025-4093

## Detection guidance (public sample)

### Firefox or Thunderbird Spawning Shell or Script Interpreter

ATT&CK: T1189

Firefox or Thunderbird launching a command shell, script host or LOLBin child process, which is consistent with post-exploitation after a browser or mail client code-execution bug. Auto-generated starting point — validate and tune in your environment before deploying. IOC matches can false-positive on shared infrastructure and decay as adversary infrastructure rotates.

```yaml
title: Firefox or Thunderbird Spawning Shell or Script Interpreter
description: Detects Firefox or Thunderbird launching a command shell, script host
  or common LOLBin as a child process. The browser and mail client normally spawn
  only copies of themselves and helpers (crashreporter, updater, pingsender), so a
  shell child suggests a successful memory-corruption or sandbox-escape exploit or
  a drive-by payload. The report is a patch advisory with no in-the-wild exploitation,
  so this is a generic post-exploitation detection and not tied to any CVE.
tags:
- attack.initial-access
- attack.t1189
logsource:
  category: process_creation
  product: windows
detection:
  selection:
    ParentImage|endswith:
    - \firefox.exe
    - \thunderbird.exe
    Image|endswith:
    - \cmd.exe
    - \powershell.exe
    - \pwsh.exe
    - \wscript.exe
    - \cscript.exe
    - \mshta.exe
    - \rundll32.exe
    - \regsvr32.exe
    - \certutil.exe
    - \bitsadmin.exe
    - \msiexec.exe
  condition: selection
falsepositives:
- Users opening a downloaded script or attachment from the browser or mail client
  with a handler that invokes a shell
- Browser extensions or native-messaging hosts that are implemented as batch or PowerShell
  scripts
level: medium
id: c0c0b5eb-b7b6-5d3a-8ee6-efadb074a9e9
status: experimental
author: Vorant
references:
- https://www.cisecurity.org/advisory/multiple-vulnerabilities-in-mozilla-products-could-allow-for-arbitrary-code-execution_2025-045
```

Behavioural rules are generated from public reporting — validate in your environment before deploying.

Source reporting: https://www.cisecurity.org/advisory/multiple-vulnerabilities-in-mozilla-products-could-allow-for-arbitrary-code-execution_2025-045

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