Quick answers
- Is CVE-2026-109778 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-109778 being exploited in the wild.
- How severe is CVE-2026-109778?
- High severity, with a CVSS score of 8.8, published 13 October 2026.
- Which products and versions are affected?
- Mozilla Firefox before 158; Mozilla Firefox ESR before 153.5; Mozilla Thunderbird before 153.5.
- Is there a fix for CVE-2026-109778?
- Yes: fixed in Firefox 158, Firefox ESR 153.5, Thunderbird 158, Thunderbird 153.5. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
- How is CVE-2026-109778 attacked?
- It is in a web application.
- Am I affected by CVE-2026-109778?
- Check whether you run Mozilla Firefox, Mozilla Firefox ESR or Mozilla Thunderbird at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
- Fixed in: Firefox 158, Firefox ESR 153.5, Thunderbird 158, Thunderbird 153.5
Technical details
A privilege escalation vulnerability exists in the WebExtensions component of Firefox and Thunderbird. The flaw allows an attacker to elevate privileges within the extension context, potentially leading to unauthorized access to browser APIs and user data. The vulnerability was patched across multiple product versions and represents a moderate-to-high risk depending on attack prerequisites.
Affected products
- Mozilla Firefox before 158
- Mozilla Firefox ESR before 153.5
- Mozilla Thunderbird before 158
- Mozilla Thunderbird before 153.5
Timeline
- 2026-10-13: disclosed