CVE-2026-98374
tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()
Description
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.
INFO
Published Date :
Oct. 7, 2026, 1:17 p.m.
Last Modified :
Oct. 7, 2026, 1:17 p.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Solution
- Update the Linux kernel to the patched version.
- Apply the specific TCP fix for retransmit_skb_hint.
- Ensure TP->retransmit_skb_hint is synchronized with skb copies.
References to Advisories, Solutions, and Tools
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CWE - Common Weakness Enumeration
While CVE identifies
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associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
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stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-98374
weaknesses.
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The following table lists the changes that have been made to the
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Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Oct. 07, 2026
Action Type Old Value New Value Added Description 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. Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/98xxx/CVE-2026-98374.json">CVE-2026-98374</a> Added Reference https://git.kernel.org/stable/c/0f87720c7e4bcab07c24888b3cf12bfe857bb90e Added Reference https://git.kernel.org/stable/c/631aa4cb45099f09e9385dd786bd291c6270bfc4 Added Reference https://git.kernel.org/stable/c/71d45049b0d631dfdbf3c65305f7fca676de023b Added Reference https://git.kernel.org/stable/c/c5b4da1f403a658c1c19766be2b426003ada419f Added Reference https://git.kernel.org/stable/c/e3ea71cb1408a013ed4e8a757b815f1a919324bd Added Reference https://git.kernel.org/stable/c/fad6d429651e748365e93ca54645accc212f0018 Added Reference https://git.kernel.org/stable/c/fe99bbeee5c5dbd3abc30721a8079ced59649d97