From: Gianmarco De Gregori Date: Wed, 10 Dec 2025 10:48:33 +0000 (+0100) Subject: mudp: fix unaligned 32-bit read when parsing peer ID X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=8bf8bead6d7cc3c743fdf2b915fbb2f3f24e7005;p=thirdparty%2Fopenvpn.git mudp: fix unaligned 32-bit read when parsing peer ID The code previously read a 32-bit value from a uint8_t buffer using a direct cast and dereference. This can cause unaligned memory access and undefined behavior on architectures that do not support unaligned reads, potentially leading to a one-packet crash. Fix this by reading the bytes individually and combining them manually. Reported-By: Joshua Rogers Found-By: ZeroPath (https://zeropath.com) Change-Id: Id0bb4c45d373437ab8dbaff7a311745f9b538cbf Signed-off-by: Gianmarco De Gregori Acked-by: Gert Doering Gerrit URL: https://gerrit.openvpn.net/c/openvpn/+/1348 Message-Id: <20251210104839.8270-1-gert@greenie.muc.de> Signed-off-by: Gert Doering --- diff --git a/src/openvpn/mudp.c b/src/openvpn/mudp.c index b03e165e4..5de3af697 100644 --- a/src/openvpn/mudp.c +++ b/src/openvpn/mudp.c @@ -209,7 +209,7 @@ multi_get_create_instance_udp(struct multi_context *m, bool *floated, struct lin /* make sure buffer has enough length to read opcode (1 byte) and peer-id (3 bytes) */ if (v2) { - uint32_t peer_id = ntohl(*(uint32_t *)ptr) & 0xFFFFFF; + uint32_t peer_id = ((uint32_t)ptr[1] << 16) | ((uint32_t)ptr[2] << 8) | ((uint32_t)ptr[3]); peer_id_disabled = (peer_id == MAX_PEER_ID); if (!peer_id_disabled && (peer_id < m->max_clients) && (m->instances[peer_id]))