CVE-2026-80849
Received Received - Intake

Use-After-Free in Linux Kernel TCP-AO Implementation

Publication date: 2026-09-04

Last updated on: 2026-09-04

Assigner: kernel.org

Description
In the Linux kernel, the following vulnerability has been resolved: net/tcp-ao: fix use-after-free of current_key on reconnect to another peer tcp_inbound_ao_hash() is called before bh_lock_sock_nested() is taken, with only rcu_read_lock() held. On the fast path for established sockets, if the rnext_keyid sent by the peer differs from current_key->sndid, the key the peer asked for is looked up and stored in current_key. The lookup is inside the RCU read side, but current_key outlives it. When the socket is disconnected and connect() is called again for another peer, tcp_ao_connect_init() unlinks every key that does not match the new peer and frees it with call_rcu(). If current_key points at such a key, it is cleared to NULL. The fast path reads sk_state only once on entry, so a softirq that got into it while the socket was still established can update current_key after that loop has already run. The update is inside the RCU read side, so it comes before the call_rcu() callback, and once the callback frees the key, current_key is left pointing at freed memory. The next transmission picks that pointer up in tcp_get_current_key(). tcp_ao_transmit_skb() then reads the traffic key from the freed object, which is the use-after-free. Wait for one grace period before unlinking, and only if a key is going to be removed. By the time tcp_connect() runs the socket is already in TCP_SYN_SENT, and TCP_AO_ESTABLISHED does not contain TCPF_SYN_SENT, so a softirq entering after the wait cannot reach the fast path, and the ones already in it have finished. The existing NULL handling in the loop is then enough.

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Meta Information

Published
2026-09-04
Last Modified
2026-09-04
Generated
2026-09-04
AI Q&A
2026-09-04
EPSS Evaluated
N/A
NVD
CVE-2026-80849
EUVD
EUVD-2026-71299

Affected Vendors & Products

Showing 1 associated CPE
Vendor Product Version / Range
linux linux_kernel *

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Exploitability

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CWE ID Description
CWE-UNKNOWN

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Executive Summary

This vulnerability is a use-after-free issue in the Linux kernel's TCP Authentication Option (TCP-AO) implementation. It occurs when a socket reconnects to a different peer, causing a key pointer to reference freed memory. The flaw arises because current_key outlives the RCU read side, allowing a softirq to update it after a key is freed, leading to potential memory corruption during subsequent transmissions.

Detection Guidance

This vulnerability involves a use-after-free in the Linux kernel's TCP-AO implementation. Detection requires checking kernel logs for TCP-AO related errors or crashes, particularly after socket reconnections. Monitor for kernel oops or panics involving tcp_ao or tcp_inbound_ao_hash functions. No specific commands are provided in the context.

Impact Analysis

This vulnerability could allow an attacker to execute arbitrary code or cause a denial-of-service condition by triggering a use-after-free in the kernel. If exploited, it may lead to system crashes, privilege escalation, or unauthorized access to sensitive data, depending on the kernel's context and security mitigations.

Compliance Impact

This vulnerability could impact compliance with GDPR and HIPAA by compromising system integrity and data confidentiality. A successful exploit may lead to unauthorized data access or system disruption, violating requirements for data protection and availability. Organizations must patch affected systems to maintain compliance.

Mitigation Strategies

Apply the Linux kernel patch that resolves this issue. Update to a kernel version containing the fix for net/tcp-ao use-after-free. If immediate patching is not possible, disable TCP-AO (TCP Authentication Option) if not required, as this vulnerability specifically affects TCP-AO functionality.

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