Enr1G

**Name of the Vulnerable Software and Affected Versions** Pomerium versions prior to 0.26.1 **Description** The Pomerium user info page, located at the `/.pomerium` endpoint, unintentionally included serialized OAuth2 access and ID tokens from the logged-in user's session. These tokens are not intended to be exposed to end users. This issue may be more severe in the presence of a cross-site scripting vulnerability in an upstream application proxied through Pomerium. If an attacker could insert a malicious script onto a web page proxied through Pomerium, that script could access these tokens by making a request to the `/.pomerium` endpoint. Upstream applications that authenticate only the ID token may be vulnerable to user impersonation using a token obtained in this manner. Note that an OAuth2 access token or ID token by itself is not sufficient to hijack a user's Pomerium session. Upstream applications should not be vulnerable to user impersonation via these tokens provided the application verifies the Pomerium JWT for each request, the connection between Pomerium and the application is secured by mTLS, or the connection between Pomerium and the application is otherwise secured at the network layer. **Recommendations** To resolve the issue, upgrade to Pomerium version 0.26.1 or later. As a temporary workaround, consider restricting access to the `/.pomerium` endpoint to minimize the risk of exploitation. Additionally, ensure that upstream applications verify the Pomerium JWT for each request, secure the connection between Pomerium and the application using mTLS, or otherwise secure the connection at the network layer.