CVE-2025-40248 vsock: Ignore signal/timeout on connect() if already established

High 7.8 Published 4 Dec 2025 Updated 5 Aug 2026

A race condition in the Linux kernel vsock implementation allows attackers to cause use-after-free or null pointer dereferences, potentially leading to system crashes or code execution.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2025-40248?

CVE-2025-40248 is a high-severity vulnerability in Linux, published on 4 Dec 2025. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

vsock: Ignore signal/timeout on connect() if already established

During connect(), acting on a signal/timeout by disconnecting an already established socket leads to several issues:

1. connect() invoking vsock_transport_cancel_pkt() -> virtio_transport_purge_skbs() may race with sendmsg() invoking virtio_transport_get_credit(). This results in a permanently elevated `vvs->bytes_unsent`. Which, in turn, confuses the SOCK_LINGER handling.

2. connect() resetting a connected socket's state may race with socket being placed in a sockmap. A disconnected socket remaining in a sockmap breaks sockmap's assumptions. And gives rise to WARNs.

3. connect() transitioning SS_CONNECTED -> SS_UNCONNECTED allows for a transport change/drop after TCP_ESTABLISHED. Which poses a problem for any simultaneous sendmsg() or connect() and may result in a use-after-free/null-ptr-deref.

Do not disconnect socket on signal/timeout. Keep the logic for unconnected sockets: they don't linger, can't be placed in a sockmap, are rejected by sendmsg().

[1]: https://lore.kernel.org/netdev/[email protected]/ [2]: https://lore.kernel.org/netdev/[email protected]/ [3]: https://lore.kernel.org/netdev/[email protected]/

Which versions are affected by CVE-2025-40248?

Linux distribution packages (40)

`kpatch-patch-4_18_0-553_30_1` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-11.el8_10`
`kpatch-patch-4_18_0-553_30_1-debuginfo` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-11.el8_10`
`kpatch-patch-4_18_0-553_30_1-debugsource` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-11.el8_10`
`kpatch-patch-4_18_0-553_40_1` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-9.el8_10`
`kpatch-patch-4_18_0-553_40_1-debuginfo` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-9.el8_10`
`kpatch-patch-4_18_0-553_40_1-debugsource` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-9.el8_10`
`kpatch-patch-4_18_0-553_53_1` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-7.el8_10`
`kpatch-patch-4_18_0-553_53_1-debuginfo` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-7.el8_10`
`kpatch-patch-4_18_0-553_53_1-debugsource` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-7.el8_10`
`kpatch-patch-4_18_0-553_72_1` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-4.el8_10`
`kpatch-patch-4_18_0-553_72_1-debuginfo` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-4.el8_10`
`kpatch-patch-4_18_0-553_72_1-debugsource` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-4.el8_10`
`kpatch-patch-4_18_0-553_85_1` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-2.el8_10`
`kpatch-patch-4_18_0-553_85_1-debuginfo` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-2.el8_10`
`kpatch-patch-4_18_0-553_85_1-debugsource` Red Hat:enterprise_linux:8::baseos	All versions	`0:1-2.el8_10`
`kpatch-patch-5_14_0-611_9_1` Red Hat:enterprise_linux:9::baseos	All versions	`0:1-3.el9_7`
`kpatch-patch-5_14_0-611_9_1-debuginfo` Red Hat:enterprise_linux:9::baseos	All versions	`0:1-3.el9_7`
`kpatch-patch-5_14_0-611_9_1-debugsource` Red Hat:enterprise_linux:9::baseos	All versions	`0:1-3.el9_7`
`kpatch-patch-4_18_0-372_131_1` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-12.el8_6`
`kpatch-patch-4_18_0-372_131_1-debuginfo` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-12.el8_6`
`kpatch-patch-4_18_0-372_131_1-debugsource` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-12.el8_6`
`kpatch-patch-4_18_0-372_137_1` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-9.el8_6`
`kpatch-patch-4_18_0-372_137_1-debuginfo` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-9.el8_6`
`kpatch-patch-4_18_0-372_137_1-debugsource` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-9.el8_6`
`kpatch-patch-4_18_0-372_145_1` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-7.el8_6`
`kpatch-patch-4_18_0-372_145_1-debuginfo` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-7.el8_6`
`kpatch-patch-4_18_0-372_145_1-debugsource` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-7.el8_6`
`kpatch-patch-4_18_0-372_158_1` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-3.el8_6`
`kpatch-patch-4_18_0-372_158_1-debuginfo` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-3.el8_6`
`kpatch-patch-4_18_0-372_158_1-debugsource` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-3.el8_6`
`kpatch-patch-4_18_0-372_170_1` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-2.el8_6`
`kpatch-patch-4_18_0-372_170_1-debuginfo` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-2.el8_6`
`kpatch-patch-4_18_0-372_170_1-debugsource` Red Hat:rhel_e4s:8.6::baseos	All versions	`0:1-2.el8_6`
`kpatch-patch-4_18_0-477_107_1` Red Hat:rhel_e4s:8.8::baseos	All versions	`0:1-3.el8_8`
`kpatch-patch-4_18_0-477_107_1-debuginfo` Red Hat:rhel_e4s:8.8::baseos	All versions	`0:1-3.el8_8`
`kpatch-patch-4_18_0-477_107_1-debugsource` Red Hat:rhel_e4s:8.8::baseos	All versions	`0:1-3.el8_8`
`kpatch-patch-4_18_0-477_120_1` Red Hat:rhel_e4s:8.8::baseos	All versions	`0:1-2.el8_8`
`kpatch-patch-4_18_0-477_120_1-debuginfo` Red Hat:rhel_e4s:8.8::baseos	All versions	`0:1-2.el8_8`
`kpatch-patch-4_18_0-477_120_1-debugsource` Red Hat:rhel_e4s:8.8::baseos	All versions	`0:1-2.el8_8`
`kpatch-patch-4_18_0-477_81_1` Red Hat:rhel_e4s:8.8::baseos	All versions	`0:1-11.el8_8`

How do I fix CVE-2025-40248?

Apply the vendor's patch.

Is CVE-2025-40248 being exploited?

There is no known exploitation of CVE-2025-40248 in the wild and no public exploit code.

Sources

Also known as AZL-71396, BELL-CVE-2025-40248, DEBIAN-CVE-2025-40248, GHSA-j4rg-4m7w-4hr3, RHSA-2026:3848, RHSA-2026:3865 and 12 more.