CVE-2026-98276 net: lock the socket in sock_gettstamp()
- Exploited in the wild
- Not known
- Fix
- Available
What is CVE-2026-98276?
CVE-2026-98276 is a high-severity vulnerability in Linux, published on 6 Oct 2026.
Official description
In the Linux kernel, the following vulnerability has been resolved:
net: lock the socket in sock_gettstamp()
sk->sk_flags must only be changed while holding the socket lock, because sock_set_flag() and sock_reset_flag() use non atomic operations (__set_bit() and __clear_bit()).
sock_gettstamp() is one of the last places where a bit of sk->sk_flags is changed from a syscall without owning the socket lock, through sock_enable_timestamp(sk, SOCK_TIMESTAMP).
sk_set_memalloc() and sk_clear_memalloc() also change sk->sk_flags without the socket lock, but their callers (nbd, iscsi_tcp, nvme-tcp, sunrpc, wireguard) need a careful audit, this will be addressed in a separate patch.
Jungwoo Lee and Wongi Lee reported an UDP socket use-after-free caused by this bug: a SIOCGSTAMPNS_NEW ioctl racing with bind() can cancel the SOCK_RCU_FREE bit that udp_lib_get_port() just set, because both threads perform a read-modify-write on the same word.
CPU 0 (bind) CPU 1 (SIOCGSTAMPNS_NEW) -------------------------------- ---------------------------- read sk_flags = F read sk_flags = F compute F | BIT(SOCK_RCU_FREE) compute F | BIT(SOCK_TIMESTAMP) store F | BIT(SOCK_RCU_FREE) sk_add_node_rcu(sk, ...) store F | BIT(SOCK_TIMESTAMP)
After the lost update, SOCK_RCU_FREE is clear while the socket is visible to lockless UDP receive lookups. sk_destruct() then frees the socket immediately instead of waiting for a RCU grace period, while the receive path still holds a reference-less pointer to it:
BUG: KASAN: slab-use-after-free in ipv4_pktinfo_prepare+0x30/0x410 Read of size 8 at addr ffff888008806610 by task exploit/207 CPU: 0 UID: 1000 PID: 207 Comm: exploit Not tainted 6.12.95+ #1 ipv4_pktinfo_prepare+0x30/0x410 udp_queue_rcv_one_skb+0x51c/0x1180 udp_unicast_rcv_skb+0x109/0x350 ip_protocol_deliver_rcu+0x14b/0x310 ip_local_deliver_finish+0x29d/0x390 ip_local_deliver+0x24d/0x2a0
Only grab the socket lock when SOCK_TIMESTAMP has to be set, to keep the common case lockless.
Which versions are affected by CVE-2026-98276?
How do I fix CVE-2026-98276?
Upgrade to a fixed version.
Is CVE-2026-98276 being exploited?
There is no known exploitation of CVE-2026-98276 in the wild and no public exploit code.
Sources
Also known as AZL-106305, BELL-CVE-2026-98276, DEBIAN-CVE-2026-98276, GHSA-qgp7-2j87-wmwc, UBUNTU-CVE-2026-98276.