CVE-2026-42177 linux-entra-sso: PRT SSO cookie can leak to attacker-controlled hosts when broad host permissions are granted
Attackers can steal Entra ID Primary Refresh Token cookies via crafted URLs if the browser extension has broad host permissions, enabling account takeover.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-42177?
CVE-2026-42177 is a medium-severity vulnerability in siemens linux-entra-sso, published on 12 May 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
linux-entra-sso is a browser plugin for Linux to SSO on Microsoft Entra ID. Prior to 1.8.1, platform/chrome/js/platform-chrome.js:69-88 registers a single declarativeNetRequest rule whose urlFilter is Platform.SSO_URL + "/*", i.e. "https://login.microsoftonline.com/*". Chrome's urlFilter without a | or || anchor is substring-matched against the full request URL. The same applied rule action is modifyHeaders that attaches the Entra ID Primary Refresh Token cookie. The Firefox adapter in platform/firefox/js/platform-firefox.js:53 performs a belt-and-braces startsWith(Platform.SSO_URL) check before injecting the header; the Chrome adapter does not. When the extension holds broad host permissions through the optional_host_permissions: ["https://*/*"] declared in platform/chrome/manifest.json:34, a main-frame navigation to a URL whose path embeds https://login.microsoftonline.com/ causes Chrome to attach the PRT cookie to the request to the attacker-controlled host. This vulnerability is fixed in 1.8.1.
Which versions are affected by CVE-2026-42177?
How do I fix CVE-2026-42177?
Upgrade to a fixed version.
Is CVE-2026-42177 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42177 exists.
Sources
Also known as DEBIAN-CVE-2026-42177, GHSA-52rj-42vh-2rxc, UBUNTU-CVE-2026-42177.