Linux Kernel IPv4 Use-After-Free Vulnerability (CVE-2026-98432)
Summary #
A use-after-free vulnerability, tracked as CVE-2026-98432, was disclosed in the IPv4 networking code of the Linux kernel. The kernel frees IP option structures right away while other kernel code may still be reading them. That can cause memory corruption when the kernel builds TCP SYN-ACK responses for pending connections, or when it moves pending connections between sockets. Connection migration is used when net.ipv4.tcp_migrate_req=1 is set or a BPF reuseport program is attached. A remote unauthenticated attacker can trigger memory corruption, kernel crash, and potential remote code execution (RCE) by sending specially crafted IPv4 TCP packets.
WatchGuard has investigated and found the following products run a vulnerable version of the Linux Kernel and are potentially affected by CVE-2026-98432: - Firebox Fireware OS - WatchGuard AP - Dimension
While Fireware OS and WatchGuard AP run vulnerable versions of the Linux kernel, they do not enable MPTCP and are not affected by the remote code execution (RCE) exploit chain circulating online.
WatchGuard Dimension runs on a vulnerable version of the Ubuntu operating system but without MPTCP enabled. We will update this advisory when a fix is available from Ubuntu.
CVE identifiers #
| CVE ID | Description | CVSS |
|---|---|---|
| CVE-2026-98432 | In the Linux kernel, the following vulnerability has been resolved: ipv4: free inet_opt and ireq_opt after an RCU grace period tcp_v4_syn_recv_sock() transfers ownership of ireq->ireq_opt to the child socket (newinet->inet_opt) without copying it. Another cpu can concurrently process a retransmitted SYN for the same request socket, and send a SYNACK from tcp_check_req(). tcp_v4_send_synack() and inet_csk_route_req() read ireq->ireq_opt under rcu_read_lock() only, and ip_build_and_send_pkt() and ip_options_build() then read opt->optlen twice. Note that the SYNACK timer itself is not an issue: it holds a reference on its request socket, and inet_csk_reqsk_queue_drop() calls timer_delete_sync() before the child can be freed. Since commit 079096f103fa ("tcp/dccp: install syn_recv requests into ehash table"), request sockets are processed without holding the listener lock, so nothing prevents the child socket from being freed while the SYNACK is still being built. TCP child sockets do not have SOCK_RCU_FREE, and inet_sock_destruct() frees inet_opt with a plain kfree(), leading to a use-after-free in ip_options_build(). A similar issue exists with request socket migration (net.ipv4.tcp_migrate_req=1, or a BPF_SK_REUSEPORT_SELECT_OR_MIGRATE program). reqsk_timer_handler() clones the request socket with inet_reqsk_clone(), so that the old request socket and its clone share the same ireq_opt, then reqsk_migrate_reset() clears the pointer in the old one. Another cpu holding a reference on the old request socket can still be using these options (sending a SYNACK, or creating a child in tcp_v4_syn_recv_sock()) when the clone is freed, and tcp_v4_reqsk_destructor() also uses a plain kfree(). Readers already use RCU, and other paths replacing inet_opt (do_ip_setsockopt(), cipso_v4_sock_setattr()...) already use kfree_rcu(). Use kfree_rcu() in inet_sock_destruct() and tcp_v4_reqsk_destructor() as well. IPv6 is not affected by the first issue, because tcp_v6_syn_recv_sock() duplicates the options. tcp_v6_reqsk_destructor() has the same migration issue with ipv6_opt, which is only set by CALIPSO. This will be addressed in a separate patch. | 9.8 |
Product status #
| Product | Affected | Not affected |
|---|---|---|
| Dimension | >= 2.0 | — |
| Fireware OS | ||
| Default | 2025.1, >= 12.0 | — |
| WatchGuard AP | >= 1.0 | — |
Solution #
Product | Status | Resolved Version |
|---|---|---|
Firebox Fireware OS | Potentially Affected | Unresolved |
WatchGuard AP | Potentially Affected | Unresolved |
Dimension | Potentially Affected | Unresolved |