CVE-2026-98374 tcp: fix use-after-free of retransmit_skb_hint in tcp_send_synack()
An unprivileged remote attacker can trigger a use-after-free in the Linux kernel TCP stack via crafted ICMP messages, potentially causing a crash or code execution.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-98374?
CVE-2026-98374 is a high-severity use after free vulnerability in Linux, published on 7 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-98374?
How do I fix CVE-2026-98374?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-98374 being exploited?
There is no known exploitation of CVE-2026-98374 in the wild and no public exploit code.
Sources
Also known as AZL-106734, BELL-CVE-2026-98374, DEBIAN-CVE-2026-98374, GHSA-2q84-vc4j-mp23, UBUNTU-CVE-2026-98374.