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CVE-2026-74938 is a mitigation bypass vulnerability in Mozilla's JavaScript garbage collection component. The issue affects Mozilla Firefox and Mozilla Thunderbird and was fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1. Available information identifies the affected area only as the JavaScript: GC component and indicates that the flaw allows an attacker to circumvent an existing security mitigation rather than directly describing a memory-safety primitive or specific vulnerable function. The vulnerability is part of a broader set of Mozilla security fixes released in August 2026.
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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.
12 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
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A specific vulnerability identified as CVE-2026-74938 affecting Ubuntu Linux LTS releases and associated mozjs and Thunderbird packages, with network attack vector and high confidentiality/integrity impact per the listed CVSS v3 vector.
A vulnerability referenced by the Thunderbird < 154.0 advisory, but not described individually in the provided content.
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.