CVE-2022-39252 (Rust, published 2022-09-29T15:15Z)
Description: value: matrix-rust-sdk is an implementation of a Matrix client-server library in Rust, and matrix-sdk-crypto is the Matrix encryption library. Prior to version 0.6, when a user requests a room key from their devices, the software correctly remembers the request. When the user receives a forwarded room key, the software accepts it without checking who the room key came from. This allows homeservers to try to insert room keys of questionable validity, potentially mounting an impersonation attack. Version 0.6 fixes this issue.
Severity: nan (CVSS v3 base score: 7.5)
Weakness: CWE-287 \u2014 Improper Authentication
When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct.
Repository: https://github.com/matrix-org/matrix-rust-sdk
Files changed:
crates/matrix-sdk-crypto/src/gossiping/machine.rs
Commit message: test(crypto): Test that we reject forwarded room keys from other users


Vulnerable code:
        let bob_machine = test_gossip_machine(alice_id());
        alice_machine.store.save_devices(&[bob_device]).await.unwrap();
            machines_for_key_share(true).await;
            machines_for_key_share(false).await;

Fixed code:
        other_machine_owner: &UserId,
        let bob_machine = test_gossip_machine(other_machine_owner);
        let second_device = ReadOnlyDevice::from_account(&alice_2_account()).await;
        second_device.set_trust_state(LocalTrust::Verified);
        alice_machine.store.save_devices(&[bob_device, second_device]).await.unwrap();
            machines_for_key_share(alice_id(), true).await;
    #[async_test]
    async fn reject_forward_from_another_user() {
        let (alice_machine, alice_account, group_session, bob_machine) =
            machines_for_key_share(bob_id(), true).await;

        // Get the request and convert it into a event.
        let requests = alice_machine.outgoing_to_device_requests().await.unwrap();
        let request = &requests[0];
        let event = request_to_event(alice_id(), alice_id(), request);

        alice_machine.mark_outgoing_request_as_sent(&request.request_id).await.unwrap();

        // Bob doesn't have any outgoing requests.
        assert!(bob_machine.outgoing_requests.is_empty());

        // Receive the room key request from alice.
        bob_machine.receive_incoming_key_request(&event);
        bob_machine.collect_incoming_key_requests().await.unwrap();
        // Now bob does have an outgoing request.
        assert!(!bob_machine.outgoing_requests.is_empty());

        // Get the request and convert it to a encrypted to-device event.
        let requests = bob_machine.outgoing_to_device_requests().await.unwrap();
        let request = &requests[0];

        let event: EncryptedToDeviceEvent = request_to_event(alice_id(), bob_id(), request);
        bob_machine.mark_outgoing_request_as_sent(&request.request_id).await.unwrap();

        // Check that alice doesn't have the session.
        assert!(alice_machine
            .store
            .get_inbound_group_session(
                room_id(),
                &bob_machine.store.account().identity_keys().curve25519.to_base64(),
                group_session.session_id()
            )
            .await
            .unwrap()
            .is_none());

        let decrypted = alice_account.decrypt_to_device_event(&event).await.unwrap();
        if let AnyDecryptedOlmEvent::ForwardedRoomKey(e) = decrypted.result.event {
            let session = alice_machine
                .receive_forwarded_room_key(decrypted.result.sender_key, &e)
                .await
                .unwrap();

            assert!(session.is_none(), "We should not receive a room key from another user");
        } else {
            panic!("Invalid decrypted event type");
        }
    }

            machines_for_key_share(alice_id(), false).await;