From 195e15421df113d7283aab2ccff8b8fb06df5465 Mon Sep 17 00:00:00 2001 From: Matt Caswell Date: Fri, 21 Jun 2024 11:51:54 +0100 Subject: [PATCH 08/10] Add ALPN validation in the client The ALPN protocol selected by the server must be one that we originally advertised. We should verify that it is. Follow on from CVE-2024-5535 Reviewed-by: Neil Horman Reviewed-by: Tomas Mraz (Merged from https://github.com/openssl/openssl/pull/24717) --- ssl/statem/extensions_clnt.c | 24 ++++++++++++++++++++++++ 1 file changed, 24 insertions(+) diff --git a/ssl/statem/extensions_clnt.c b/ssl/statem/extensions_clnt.c index 1ab3c13d57..ff9c009ee5 100644 --- a/ssl/statem/extensions_clnt.c +++ b/ssl/statem/extensions_clnt.c @@ -1590,6 +1590,8 @@ int tls_parse_stoc_alpn(SSL_CONNECTION *s, PACKET *pkt, unsigned int context, X509 *x, size_t chainidx) { size_t len; + PACKET confpkt, protpkt; + int valid = 0; /* We must have requested it. */ if (!s->s3.alpn_sent) { @@ -1608,6 +1610,28 @@ int tls_parse_stoc_alpn(SSL_CONNECTION *s, PACKET *pkt, unsigned int context, SSLfatal(s, SSL_AD_DECODE_ERROR, SSL_R_BAD_EXTENSION); return 0; } + + /* It must be a protocol that we sent */ + if (!PACKET_buf_init(&confpkt, s->ext.alpn, s->ext.alpn_len)) { + SSLfatal(s, SSL_AD_INTERNAL_ERROR, ERR_R_INTERNAL_ERROR); + return 0; + } + while (PACKET_get_length_prefixed_1(&confpkt, &protpkt)) { + if (PACKET_remaining(&protpkt) != len) + continue; + if (memcmp(PACKET_data(pkt), PACKET_data(&protpkt), len) == 0) { + /* Valid protocol found */ + valid = 1; + break; + } + } + + if (!valid) { + /* The protocol sent from the server does not match one we advertised */ + SSLfatal(s, SSL_AD_DECODE_ERROR, SSL_R_BAD_EXTENSION); + return 0; + } + OPENSSL_free(s->s3.alpn_selected); s->s3.alpn_selected = OPENSSL_malloc(len); if (s->s3.alpn_selected == NULL) { -- 2.46.0