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CVE-2026-84119 is a high-severity use-after-free vulnerability in the DOM Navigation component of Mozilla Firefox and Thunderbird. The memory-lifetime flaw can enable a sandbox escape, allowing attacker-controlled content to break out of browser sandbox restrictions. It is fixed in Firefox 155, Firefox ESR 115.40, 140.15, and 153.2, and Thunderbird 155, 140.15, and 153.2.
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What it means. What to do now. Patch path, mitigations, and the assume-compromise checklist.
What an attacker gets, and what they’ve been doing with it.
If you can’t patch tonight, do this now.
Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
Products and vendors Mallory has correlated with this vulnerability. Open in Mallory to drill down to specific CPE configurations and version ranges.
Vendor-confirmed product mapping. Mallory continuously reconciles this list against your asset inventory.
15 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A vulnerability referenced by the Mozilla Firefox ESR 115.40 plugin; no technical vulnerability details are provided.
A vulnerability addressed by the Mozilla Firefox ESR 140.15 update; no technical vulnerability details are provided.
A vulnerability affecting Mozilla Firefox ESR addressed by the referenced Firefox ESR update; the content provides no technical flaw description.
A vulnerability addressed by the referenced Mozilla Firefox ESR security update. No technical flaw details are provided.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.