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CVE-2026-74956 is a same-origin policy bypass vulnerability in the DOM Service Workers component of Mozilla Firefox and Mozilla Thunderbird. The flaw allows browser security boundaries enforced by the same-origin policy to be bypassed through Service Workers behavior, enabling cross-origin access that should normally be restricted. Mozilla reports the issue as fixed in Firefox 154, Firefox ESR 153.1, Thunderbird 154, and Thunderbird 153.1.
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What an attacker gets, and what they’ve been doing with it.
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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 published vulnerability tracked as CVE-2026-74956, referenced by a Nessus plugin as affecting Ubuntu Linux-related mozjs and Thunderbird package contexts. The content provides CVSS data and indicates no known exploits are available, but does not describe the underlying flaw type.
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.