CVE-2026-80849: Linux Vulnerability

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.

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= 0a3a809089eb1d4a0a2fd0c16b520d603988c859, < 84a93b4e012587d0a4a84ffb23ec6da18e9d85f9; >= 0a3a809089eb1d4a0a2fd0c16b520d603988c859, < 73fde8fe4469f4ed8f0afcc0b9d6413002a9e6b3; >= 0a3a809089eb1d4a0a2fd0c16b520d603988c859, < e54ad693eddb40c595add013f545354c538e325b; >= 0a3a809089eb1d4a0a2fd0c16b520d603988c859, < 2857dcbd03cf3354af0fba1b65c6a260fb43811a; >= 0a3a809089eb1d4a0a2fd0c16b520d603988c859, < da4471557f279d0f56605158a625bb6e49ef7d41
Linux	Linux	6.7

References

Timeline

Published: Sep 4, 2026
Last Modified: Sep 4, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-80849?

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.

How severe is CVE-2026-80849?

Severity scoring for CVE-2026-80849 is pending analysis.

How do I fix CVE-2026-80849?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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