CVE-2026-98374
Received Received - Intake

Use-After-Free in Linux Kernel TCP Stack

Publication date: 2026-10-07

Last updated on: 2026-10-07

Assigner: kernel.org

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.

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Meta Information

Published
2026-10-07
Last Modified
2026-10-07
Generated
2026-10-07
AI Q&A
2026-10-07
EPSS Evaluated
N/A
NVD
CVE-2026-98374
EUVD
EUVD-2026-94323

Affected Vendors & Products

Showing 8 associated CPEs
Vendor Product Version / Range
Linux Linux c31b70c9968fe9c4194d1b5d06d07596a3b680de
Linux Linux c31b70c9968fe9c4194d1b5d06d07596a3b680de
Linux Linux c31b70c9968fe9c4194d1b5d06d07596a3b680de
Linux Linux c31b70c9968fe9c4194d1b5d06d07596a3b680de
Linux Linux c31b70c9968fe9c4194d1b5d06d07596a3b680de
Linux Linux c31b70c9968fe9c4194d1b5d06d07596a3b680de
Linux Linux c31b70c9968fe9c4194d1b5d06d07596a3b680de
Linux Linux 5.11

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Exploitability

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KEV
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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability is a use-after-free flaw in the Linux kernel's TCP implementation. It occurs in the tcp_send_synack() function when handling TCP Fast Open (TFO) connections. The issue arises when a cloned SYN packet is replaced on the retransmit queue, freeing the original packet but leaving a dangling pointer in the retransmit_skb_hint variable. This pointer can later be used unsafely, leading to memory corruption and potential system crashes.

Detection Guidance

This vulnerability is specific to the Linux kernel's TCP implementation and may not have direct detection commands. Monitor kernel logs for KASAN errors related to tcp_mark_skb_lost or tcp_simple_retransmit. Check for unexpected retransmissions or crashes in TCP connections.

Impact Analysis

An attacker could exploit this to cause a denial-of-service (DoS) condition by crashing the system. If successful, it may lead to kernel panic, system instability, or unauthorized access in rare cases. Systems using vulnerable Linux kernel versions with TCP Fast Open enabled are at risk.

Compliance Impact

This vulnerability is a use-after-free flaw in the Linux kernel's TCP implementation that could lead to memory corruption or crashes. While it does not directly impact data privacy or security controls required by GDPR or HIPAA, such kernel vulnerabilities may indirectly affect compliance by compromising system stability or enabling denial-of-service conditions that disrupt regulated operations.

Mitigation Strategies

Update your Linux kernel to the latest stable version that includes the fix for this issue. If immediate patching is not possible, consider disabling TCP Fast Open (TFO) as a temporary workaround to prevent exploitation.

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