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CVE-2026-84124 is a high-severity use-after-free vulnerability in Mozilla’s DOM: Core & HTML component. Incorrect object-lifetime handling can leave a stale reference to freed memory during DOM processing, creating a memory-corruption condition. It affects releases before Firefox 155, Firefox ESR 140.15 and 153.2, Thunderbird 155, and Thunderbird ESR 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.
13 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A vulnerability addressed by the referenced Fedora Firefox/NSS advisory; no flaw-specific description is supplied.
A use-after-free vulnerability in Firefox's DOM: Core & HTML component.
A vulnerability addressed by the Mozilla Firefox ESR 140.15 update; no technical vulnerability details are provided.
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.