Product: Starscream websocket library Severity: LOW CVE Reference: CVE-2017-5887 Type: SSL Pinning bypass Abstract -------- WebSocket.swift in Starscream before 2.0.4 allows an SSL Pinning bypass because pinning occurs in the stream function (this is too late; pinning should occur in the initStreamsWithData function). Description ----------- The open-source Starscream library provides a SWIFT implementation of the websocket framework. It allows iOS applications to send and receive messages via a dedicated websocket channel. Applications using the Starscream library (up to and including version 2.0.3) were vulnerable to potential information disclosure due to an incorrect implementation of SSL pinning during the websocket handshake. Impact ------ An attacker can intercept the initial websocket handshake GET request, which may potentially contain sensitive information (e.g. session tokens, cookies). An attacker could possibly misuse this information to attack the target application. Cause ----- The code of the library contains a vulnerability whereby the SSL pinning is executed only on the websocket TCP connection itself, but not for the initial handshake request. Solution -------- Upgrade to version 2.0.4. Technical details ----------------- The cause of the problem was in the implementation of the initial connection (referencing initStreamsWithData version 1.1.4 where we first discovered the issue). After configuring the streams with the SSL context, the method proceeds to open the connection and writes the initial upgrade connection directly to the stream as soon as hasSpaceAvailable returns true. The actual pinning is done only after the initial connection is established. The fix consisted in checking the pinned certificates BEFORE any byte is sent through the stream and closing the connection immediately if the check fails. Credits ------- Vulnerability was discovered by Lukas Futera and Giuliano Galea of Centralway Numbrs AG. Disclosure timeline ------------------- 28.2.2017 Vulnerability reported to vendor 07.3.2017 Vulnerability acknowledgment by vendor 14.3.2017 Vendor published initial patch 28.3.2017 New version released 21.4.2017 Advisory published -- This message is for the attention of the intended recipient(s) only. It may contain confidential, proprietary and/or legally privileged information. Use, disclosure and/or retransmission of information contained in this email may be prohibited. If you are not an intended recipient, you are kindly asked to notify the sender immediately (by reply e-mail) and to permanently delete this message. Thank you.
