Mozilla patches dozens of Firefox, Thunderbird flaws
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CERT-FR advises patching Firefox, Firefox ESR and Thunderbird for dozens of vulnerabilities enabling privilege escalation, data exposure and denial of service.
CERT-FR has issued an advisory consolidating five Mozilla security bulletins (MFSA2026-106 through MFSA2026-110) published on 13 October 2026, covering a large number of vulnerabilities across Firefox, Firefox ESR and Thunderbird. The flaws collectively allow an attacker to cause privilege escalation, remote denial of service, and breaches of data confidentiality and integrity, as well as bypass security policy controls. No single root cause or exploitation chain is detailed in this bulletin; Mozilla's own advisories provide per-CVE technical detail.
Affected versions are Firefox below 158, Firefox ESR below 115.43 and below 153.5, and Thunderbird below 153.5 and below 158. There is no indication in this advisory of active exploitation in the wild; this is a routine vendor patch cycle. Defenders should prioritize updating all affected Mozilla products to the fixed versions referenced in the bulletins, with particular attention to ESR deployments common in managed enterprise environments.
Given the volume of CVEs (over 80) spanning multiple severity categories including privilege escalation and confidentiality impacts, organizations running Firefox or Thunderbird should treat this as a standard but broad patch management action, verifying update deployment across all endpoints running the listed products.
Mentioned in this report
Source reporting: https://www.cert.ssi.gouv.fr/avis/CERTFR-2026-AVI-1305
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