Lightpanda is a headless browser designed for AI and automation. Prior to 0.2.9, Lightpanda fetch() and XMLHttpRequest unconditionally attached session cookies to every HTTP request, ignoring credentials: omit, credentials: same‑origin, credentials: include, and XMLHttpRequest.withCredentials. This allowed an attacker‑controlled origin in a Lightpanda session to issue authenticated cross‑origin requests against a victim origin, forcing the browser to send session cookies on cross‑origin requests regardless of the specified credentials mode and enabling the attacker to impersonate a user, access or modify resources on the victim domain. The weakness is classified as CWE‑346.

The flaw exists in the Lightpanda‑io browser before version 0.2.9. Users employing any Lightpanda build earlier than 0.2.9 are vulnerable. No other vendors or products are listed as affected.

The CVSS score of 9.3 categorizes this as a critical vulnerability, and the EPSS score of less than 1% indicates a low likelihood of real‑world exploitation at the time of analysis. The issue has not been listed in CISA’s KEV catalog. The most likely attack vector involves an attacker who can run or inject JavaScript in a Lightpanda session—such as through automated testing, web scraping, or malicious extensions—using the session to impersonate a trusted user on a different origin.