Opera GX browser GX Mods auto-install CSS injection patched security flaw
Vulnerability
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A critical Opera GX browser flaw in GX Mods let malicious websites auto-install a customization mod and inject CSS across every page, creating zero-click cross-site data theft risk for victims. The install happened without a permission prompt through a hidden frame and a downloaded .crx package, giving the attacker styling control beyond a single site. Opera patched the issue on May 8, and the proof of concept was later published on July 3 and tested on Opera GX 127.0.5778.41 after the fix shipped.
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Timeline
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06.07.2026 17:15 2 articles · 13d ago
Opera GX browser GX Mods auto-install CSS injection patched security flaw
Initial DisclosureResearchers found that a hidden-frame download could auto-install a GX Mods package in Opera GX and spread CSS across every page the browser opened. The proof of concept showed zero-user-interaction data theft from visited sites.
Show sources
- Opera GX Flaw Let Sites Auto-Install Mods to Steal Data — www.infosecurity-magazine.com — 06.07.2026 17:15
- Opera GX Flaw Let Sites Auto-Install Mods to Steal Data — www.infosecurity-magazine.com — 06.07.2026 17:15