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CVE-2026-84118 is a use-after-free memory-safety vulnerability in the JavaScript garbage-collection component used by Mozilla Firefox and Thunderbird. The flaw is fixed in Firefox 155, Firefox ESR 153.2, Thunderbird 155, and Thunderbird ESR 153.2.
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1 valid exploit after Mallory filtered fakes, detection scripts, and README-only repos.
The repository contains a Markdown technical write-up and one JavaScript proof of concept, poc.js. It is not part of a known exploit framework and has no network, browser-delivered, or remote-control component; it must be run locally with a vulnerable SpiderMonkey JS shell. The PoC configures GC empty-chunk retention to zero, allocates 300 retained “magnet” Symbols and 150,000 disposable Symbols for heap grooming, creates a Symbol referenced through a cross-compartment CacheIR path, drops strong references, performs zone-scoped GCs, waits for background decommit to unmap an empty chunk, and performs a final GC. Per the included analysis, SpiderMonkey 154 incorrectly omits forwarding/fixup of a weak CacheIR Symbol edge after atom-zone compaction, leaving a dangling pointer. The final GC sweep dereferences metadata through that stale pointer and crashes while accessing a null Zone field. README claims discuss possible read/oracle and chained research implications, but the repository contains only the deterministic SIGSEGV PoC and no escalation implementation.
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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 addressed by the Fedora 44 Thunderbird update.
A use-after-free flaw in the JavaScript garbage-collection component.
A vulnerability addressed by the Fedora 45 Thunderbird security update; the vulnerability type is not specified.
A use-after-free vulnerability in Firefox's JavaScript garbage-collection component.
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.