Mozilla advisory AV26-1100 covers Firefox, ESR and Thunderbird flaws
Original title: Mozilla security advisory (AV26-1100)
Canada’s Cyber Centre lists builds before Firefox 159, ESR 115.44 and 153.6, and matching Thunderbird versions.
On October 28, 2026, the Canadian Centre for Cyber Security published Mozilla security advisory AV26-1100. As of October 27, 2026, Mozilla is affected by vulnerabilities in Firefox before 159, Firefox ESR before 115.44 and before 153.6, and Thunderbird before 159 and before 153.6. The centre points to Mozilla Foundation Security Advisories 2026-118 through 2026-122 and tells users and administrators to review those links and apply necessary updates as they become available.
Unconfirmed: The notice does not name the flaws, their severity, or whether updates are already available.
- Serial number AV26-1100 is dated October 28, 2026.
- Affected status is given as of October 27, 2026.
- Five Mozilla Foundation advisories, 2026-118 through 2026-122, are linked.
- No CVE identifiers or exploitation status appear in the notice.
Impact: Unspecified vulnerabilities in Firefox, Firefox ESR and Thunderbird.
| Product | Affected |
|---|---|
| Mozilla Firefox | Prior to 159 |
| Mozilla Firefox ESR | Prior to 115.44 and prior to 153.6 |
| Mozilla Thunderbird | Prior to 159 and prior to 153.6 |
- 1.Review Mozilla Foundation Security Advisories 2026-118 through 2026-122.
- 2.Apply necessary Firefox, Firefox ESR and Thunderbird updates as they become available.
- Vendors
- Mozilla
- Products
- FirefoxFirefox ESRThunderbird
- Organizations
- Canadian Centre for Cyber Security
From the original article
1 min read at cyber.gc.ca
Serial number: AV26-1100 Date: October 28, 2026 As of October 27, 2026, Mozilla is affected by vulnerabilities in the following products: Firefox Prior to 159 Firefox ESR Prior to 115. 44 Prior to 153. 6 Thunderbird Prior to 159 Prior to 153.
cyber.gc.ca
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