CVE-2026-98276
net: lock the socket in sock_gettstamp()
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.
INFO
Published Date :
Oct. 6, 2026, 9:18 a.m.
Last Modified :
Oct. 6, 2026, 9:18 a.m.
Remotely Exploit :
No
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Solution
- Apply the provided patch to lock the socket correctly.
- Audit callers of sk_set_memalloc() and sk_clear_memalloc().
- Ensure all socket flag changes are atomic or locked.
- Update the Linux kernel to the latest secure version.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-98276.
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-98276 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-98276
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
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CVE-2026-98276 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-98276 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Oct. 06, 2026
Action Type Old Value New Value Added 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. Added Affected New affected value received. <a href="https://github.com/CVEProject/cvelistV5/blob/main/cves/2026/98xxx/CVE-2026-98276.json">CVE-2026-98276</a> Added Reference https://git.kernel.org/stable/c/17b2a1eb97fdb2a2cbaeab3b146b26797ea9311f Added Reference https://git.kernel.org/stable/c/18899e2e4023369a8f7739c2255a59a9748d8d17 Added Reference https://git.kernel.org/stable/c/1f73253add8365d0dad0a4f421acaa8c21d20cef Added Reference https://git.kernel.org/stable/c/3b12d3967e96f1b7b977d9fc352ae29a1b299a82 Added Reference https://git.kernel.org/stable/c/88c804847dd87dc613b771b392ccecdb94725032 Added Reference https://git.kernel.org/stable/c/899650bbf985b7bfd2a7b808357df9b16e6d6959 Added Reference https://git.kernel.org/stable/c/9ed55f3dbef4f4adfe65eb03b0c35c53229a8490 Added Reference https://git.kernel.org/stable/c/d9f96bc2d822501f84d1caa6275a2c6b316ca2c4