From: Maximilian Ammann via Fulldisclosure <fulldisclosure () seclists org>
Date: Tue, 17 Jan 2023 12:12:43 +0100
# wolfSSL before 5.5.0: Denial-of-service with session resumption ================================================================= ## INFO ======= The CVE project has assigned the id CVE-2022-38152 to this issue. Severity: 7.5 HIGH Affected version: before 5.5.0 End of embargo: Ended August 30, 2022 Blog Post: https://blog.trailofbits.com/2023/01/12/wolfssl-vulnerabilities-tlspuffin-fuzzing-ssh/ ## SUMMARY ========== When a TLS 1.3 client connects to a wolfSSL server and SSL_clear is called on its session, the server crashes with a segmentation fault. The bug occurs after a client performs a handshake against a wolfSSL server and then closes the connection. If the server reuses the previous session structure (struct WOLFSSL) by calling wolfSSL_clear(WOLFSSL* ssl) on it, the next received Client Hello, which resumes the previous session, crashes the server. Note, that this bug only exists in resumed handshakes using TLS session resumption. This bug was discovered using the novel symbolic-model-guided fuzzer tlspuffin. ## DETAILS ========== Line numbers below are valid for the wolfSSL Git tag v5.4.0-stable. The vulnerability is exploitable with default compilation flags. If the --enable-postauth flag is used, then this bug is no longer exploitable. When creating a new TLS session (represented by a struct WOLFSSL), a struct called arrays is allocated in internal.c:6652. ``` int InitSSL(WOLFSSL* ssl, WOLFSSL_CTX* ctx, int writeDup) { ... ssl->arrays = (Arrays*)XMALLOC(sizeof(Arrays), ssl->heap, DYNAMIC_TYPE_ARRAYS); ... } ``` Note that this function is only called when creating a new session structure using wolfSSL_new. After a handshake is done, resources related to it are freed by default using the FreeHandshakeResources function in line ssl.c:3735. This frees the memory behind ssl->arrays and sets the pointer to NULL. ``` void FreeHandshakeResources(WOLFSSL* ssl) { ... if (!ssl->options.tls1_3) FreeArrays(ssl) ... } void FreeArrays(WOLFSSL* ssl) { ... ssl->arrays = NULL; } ``` If the compile flag --enable-postauth is not set, the variable options.tls1_3 is false, and therefore the arrays are freed. If --enable-postauth is set, then the arrays are not freed. The above code is executed during the handshake of a fresh session. Users of wolfSSL might not allocate a new session by using wolfSSL_new(), but reuse a previous struct WOLFSSL. This can be done by calling wolfSSL_clear(WOLFSSL* ssl) on the previous session and reusing the struct. The next abbreviated handshake, which resumes the previous connection, will now cause a segmentation fault in tls13.c:5296. The segmentation fault occurs because the arrays pointer still points to NULL as InitSSL is not called before the Client Hello is handled. ## AFFECTED VERSIONS ==================== wolfSSL 5.3.0 and 5.4.0 are affected The server needs to handle sessions in a non-default way by using wolfSSL_clear ## SUGGESTED REMEDIATION ======================== After a session has been cleared and is reused for the next client, it should be reinitialized. _______________________________________________ Sent through the Full Disclosure mailing list https://nmap.org/mailman/listinfo/fulldisclosure Web Archives & RSS: https://seclists.org/fulldisclosure/
