Firefox for iOS hosted Reader mode on an unauthenticated local web server that allows other applications running on the same device to request arbitrary URLs, causing the response to be rendered with the signed‑in user's cookies. This flaw can enable an attacker to retrieve pages that include sensitive user data (such as session identifiers, stored login credentials, or personal information) by simply accessing the local web server. The primary consequence is the leakage of confidential information to unauthenticated third‑party apps on the device.

The vulnerability affects Firefox for iOS in all versions prior to 151.0. No other vendors or product versions were reported as impacted in the CNA data. Users running older builds of the mobile browser are potentially exposed.

The flaw is exploitable locally; an attacker only needs to run an application on the device that is able to connect to the local web server, which is unprotected and requires no authentication. EPSS data is unavailable, but because the attack vector is local and the flaw can reveal session cookies, the risk is considered high. The vulnerability is not listed in the CISA KEV catalog, however the impact warrants immediate remediation by updating to a fixed release.