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CVE-2026-100803 is a same-origin policy bypass vulnerability in Mozilla Firefox's WebExtensions component. It affects Firefox releases prior to Firefox 157, Firefox ESR 153.4, Firefox ESR 115.42, and Firefox ESR 140.17.
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Patch, then assume compromise.
No public exploits tracked yet. Mallory keeps watching.
No public exploit code observed for this vulnerability.
14 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A network-reachable critical vulnerability tracked as CVE-2026-100803, with CVSS v3 vector CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. The notice identifies Debian Linux 12.0, 13.0, and 14.0, including Firefox ESR package context, as affected CPE/package contexts. The underlying technical flaw type is not specified.
A same-origin policy bypass vulnerability in Firefox's WebExtensions component.
A vulnerability addressed by the Mozilla Firefox ESR 115.42 update; no technical flaw details are provided.
A vulnerability addressed by a Slackware Mozilla Firefox package update; no technical vulnerability 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.