CVE-2026-80849: Linux kernel · net/tcp-ao: fix use-after-free of current_key on reconnect to another peer
Affects Linux kernelSource GCVE Database
Not known to be exploited.
Data as of 26 Oct 2026, 13:47 UTC
Rated by Threat Radar · CVSS not yet scored by NVD
- EPSS
- 0.1% chance of exploitation in 30 days – higher than 6% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Exploitation evidence
Disclosed: evidence found.
CVE published 4 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors
A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlinux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlinux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 26.04 LTSlinux-gkepkg:deb/ubuntu/linux-gke?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.
AI-suggested
A fix has been implemented in the Linux kernel to address this use-after-free vulnerability by introducing a wait for an RCU grace period before unlinking keys. Users should apply the official kernel updates that include this patch. Since this is a kernel-level issue, upgrading to a patched kernel version is the recommended remediation. Patch status is not explicitly stated in the provided data; users should consult their Linux distribution or vendor advisories for the exact fixed versions and update accordingly.
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.
References
- nvd.nist.gov/vuln/detail/CVE-2026-80849 (opens in a new tab)
- git.kernel.org/stable/c/2857dcbd03cf3354af0fba1b65c6a260fb43811a (opens in a new tab)
- git.kernel.org/stable/c/73fde8fe4469f4ed8f0afcc0b9d6413002a9e6b3 (opens in a new tab)
- git.kernel.org/stable/c/84a93b4e012587d0a4a84ffb23ec6da18e9d85f9 (opens in a new tab)
- git.kernel.org/stable/c/da4471557f279d0f56605158a625bb6e49ef7d41 (opens in a new tab)
- git.kernel.org/stable/c/e54ad693eddb40c595add013f545354c538e325b (opens in a new tab)
- ubuntu.com/security/CVE-2026-80849 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-80849 (opens in a new tab)
- git.kernel.org/linus/da4471557f279d0f56605158a625bb6e49ef7d41 (opens in a new tab)