CVE-2026-98374
UnknownSummary
In the Linux kernel, a use-after-free vulnerability exists in tcp_send_synack() involving retransmit_skb_hint. When tcp_send_synack() replaces the cloned SYN skb at the head of the retransmit queue with a copy, it frees the original but tp->retransmit_skb_hint still points to the freed object, which can be exploited by an unprivileged TFO client to trigger a use-after-free.
Risk Assessment
An attacker could exploit the vulnerability to trigger a use-after-free in the kernel, potentially leading to a system crash or possible code execution with kernel privileges.
Recommendation
Update the Linux kernel to a version containing the fix that synchronizes the retransmit_skb_hint with the copy.
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See all- CVE-2026-98373Unknown
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack() When tcp_send_synack() replaces the cloned SYN skb at the head of the retransmit queue with a copy, it frees the original with tcp_rtx_queue_unlink_and_free() and only repairs tp->highest_sack. tp->retransmit_skb_hint keeps pointing at the freed skbuff_fclone_cache object. The dangling hint is read in tcp_verify_retransmit_hint() and used as the root of the rbtree walk in tcp_xmit_retransmit_queue(). An unprivileged TFO client (sendmsg(MSG_FASTOPEN)) can arm the hint with an attacker-supplied ICMP fragmentation-needed message, after which a simultaneous open frees the armed SYN skb: BUG: KASAN: slab-use-after-free in tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316) Read of size 4 at addr ffff88800604d928 by task swapper/1/0 Call Trace: tcp_mark_skb_lost (net/ipv4/tcp_input.c:1316) tcp_simple_retransmit (net/ipv4/tcp_input.c:3158) tcp_v4_err (net/ipv4/tcp_ipv4.c:587) Sync the hint to the copy.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS

