Headline
CVE-2023-30861: Merge pull request from GHSA-m2qf-hxjv-5gpq · pallets/flask@70f906c
Flask is a lightweight WSGI web application framework. When all of the following conditions are met, a response containing data intended for one client may be cached and subsequently sent by the proxy to other clients. If the proxy also caches Set-Cookie headers, it may send one client’s session cookie to other clients. The severity depends on the application’s use of the session and the proxy’s behavior regarding cookies. The risk depends on all these conditions being met.
- The application must be hosted behind a caching proxy that does not strip cookies or ignore responses with cookies.
- The application sets
session.permanent = True - The application does not access or modify the session at any point during a request.
SESSION_REFRESH_EACH_REQUESTenabled (the default).- The application does not set a
Cache-Controlheader to indicate that a page is private or should not be cached.
This happens because vulnerable versions of Flask only set the Vary: Cookie header when the session is accessed or modified, not when it is refreshed (re-sent to update the expiration) without being accessed or modified. This issue has been fixed in versions 2.3.2 and 2.2.5.
Expand Up @@ -501,6 +501,11 @@ def getitem(): def setdefault(): return flask.session.setdefault(“test", “default”)
@app.route(“/clear”) def clear(): flask.session.clear() return “”
@app.route(“/vary-cookie-header-set”) def vary_cookie_header_set(): response = flask.Response() Expand Down Expand Up @@ -533,11 +538,29 @@ def expect(path, header_value="Cookie”): expect(“/get”) expect(“/getitem”) expect(“/setdefault”) expect(“/clear”) expect(“/vary-cookie-header-set”) expect("/vary-header-set", “Accept-Encoding, Accept-Language, Cookie”) expect("/no-vary-header", None)
def test_session_refresh_vary(app, client): @app.get(“/login”) def login(): flask.session[“user_id”] = 1 flask.session.permanent = True return “”
@app.get(“/ignored”) def ignored(): return “”
rv = client.get(“/login”) assert rv.headers[“Vary”] == “Cookie” rv = client.get(“/ignored”) assert rv.headers[“Vary”] == “Cookie”
def test_flashes(app, req_ctx): assert not flask.session.modified flask.flash(“Zap”) Expand Down
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When all of the following conditions are met, a response containing data intended for one client may be cached and subsequently sent by a proxy to other clients. If the proxy also caches `Set-Cookie` headers, it may send one client's `session` cookie to other clients. The severity depends on the application's use of the session, and the proxy's behavior regarding cookies. The risk depends on _all_ these conditions being met. 1. The application must be hosted behind a caching proxy that does not strip cookies or ignore responses with cookies. 2. The application sets [`session.permanent = True`](https://flask.palletsprojects.com/en/2.3.x/api/#flask.session.permanent). 2. The application does not access or modify the session at any point during a request. 4. [`SESSION_REFRESH_EACH_REQUEST`](https://flask.palletsprojects.com/en/2.3.x/config/#SESSION_REFRESH_EACH_REQUEST) is enabled (the default). 5. The application does not set a `Cache-Control` header to indicate that a page is private o...