Executive brief
Zen Browser, a web browser based on Firefox, contains a vulnerability in how it handles RSS feeds. While the browser checks that the main feed address is a standard web link, it fails to verify the individual links within that feed. This could allow a malicious or compromised RSS feed to force the browser to open tabs using restricted or dangerous internal addresses, potentially leading to unauthorized actions within the browser interface.
Technical details
A vulnerability exists in Zen Browser's RSS live-folder manager where item links within a feed are not restricted to http or https schemes. While the top-level feed URL is validated in promptForFeedUrl, individual item.url values are mapped and passed directly to gBrowser.addTrustedTab() without further validation. An attacker who controls an RSS feed can include items with non-web schemes (such as file:, chrome:, or about:). If a user adds this feed, the browser will create pinned lazy tabs for these items, potentially bypassing security boundaries intended for ordinary web content. This issue is resolved in version 1.19.12b by implementing scheme validation for all item URLs.
Affected products
- Zen Browser Zen Browser < 1.19.12b
Timeline
- 2026-05-08: advisory: GitHub security advisory published
- 2026-05-11: disclosed: CVE published to NVD
- 2026-05-11: patched: Vulnerability fixed in version 1.19.12b