guzzlehttp/guzzle versions before 7.15.1 contain an information disclosure vulnerability in RedirectMiddleware. When the optional allow_redirects.referer setting is enabled, the middleware copies the URI fragment (the portion after '#') from the referring request into the generated Referer header when following a same-scheme redirect (e.g., HTTPS to HTTPS). An attacker who controls the redirect destination can read this fragment from the incoming Referer header, potentially disclosing one-time login secrets, access tokens, state values, or other sensitive client data to a server never meant to receive it. The referer setting is disabled by default. Fixed in 7.15.1, which strips the fragment before generating the Referer value.

Affected: Packagist: guzzlehttp/guzzle

### Impact

When the optional `referer` redirect setting is enabled, affected versions of `RedirectMiddleware` can copy the fragment from the referring request URI into a generated `Referer` header. A URI fragment is the part after `#`. It is handled locally by the client and is not part of the HTTP request target, so the server handling the original request does not receive it. A generated `Referer` tells the redirect destination which URI led to the request. Guzzle correctly removes user information from that value, but retains the fragment when it follows a redirect to the same scheme, such as HTTPS to HTTPS. For example, an initial URI ending in `#secret` is sent without the fragment, but the redirect destination can receive a `Referer` ending in `#secret`. This behavior affects both the cURL and stream handlers.

An attacker who controls the redirect destination can read the fragment from the incoming header, including through request logs or application code. If the fragment contains a one-time login secret, access token, state value, or other private client data, it is disclosed to a server that was never meant to receive it. Exploitation requires the application to enable `allow_redirects.referer`, make a request to a URI with a sensitive fragment, and follow a same-scheme redirect to a less-trusted destination.

The `referer` setting is disabled by default. Applications that leave it disabled, do not put sensitive data in URI fragments, do not follow redirects, or o…

Affected: Ubuntu:24.04:LTS: guzzle, Ubuntu:26.04:LTS: guzzle

guzzlehttp/guzzle versions before 7.15.1 contain an information disclosure vulnerability in RedirectMiddleware. When the optional allow_redirects.referer setting is enabled, the middleware copies the URI fragment (the portion after '#') from the referring request into the generated Referer header when following a same-scheme redirect (e.g., HTTPS to HTTPS). An attacker who controls the redirect destination can read this fragment from the incoming Referer header, potentially disclosing one-time login secrets, access tokens, state values, or other sensitive client data to a server never meant to receive it. The referer setting is disabled by default. Fixed in 7.15.1, which strips the fragment before generating the Referer value.