# 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.

- **Severity:** Medium 5.3 (`CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:N/A:N`)
- **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:** Yes
- **Published:** 12 May 2026
- **Updated:** 13 May 2026
- **Also known as:** DEBIAN-CVE-2026-42177, GHSA-52rj-42vh-2rxc, UBUNTU-CVE-2026-42177

## 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.

Weakness: CWE-436 (Interpretation Conflict), CWE-284 (Improper Access Control)

## 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.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42177 and fix it if it is affected.

What it is: 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.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42177 exists.

Affected product: siemens linux-entra-sso. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-42177/ (Markdown: https://insights.sbomify.com/CVE-2026-42177/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42177
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42177
- OSV: https://osv.dev/vulnerability/CVE-2026-42177

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42177/
Summaries are generated and may contain mistakes; the official description above is the record.