CVE-2025-40255 net: core: prevent NULL deref in generic_hwtstamp_ioctl_lower()
A local attacker can crash the Linux kernel by triggering a null pointer dereference in the network timestamping ioctl handler.
- 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-2025-40255?
CVE-2025-40255 is a 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:
net: core: prevent NULL deref in generic_hwtstamp_ioctl_lower()
The ethtool tsconfig Netlink path can trigger a null pointer dereference. A call chain such as:
tsconfig_prepare_data() -> dev_get_hwtstamp_phylib() -> vlan_hwtstamp_get() -> generic_hwtstamp_get_lower() -> generic_hwtstamp_ioctl_lower()
results in generic_hwtstamp_ioctl_lower() being called with kernel_cfg->ifr as NULL.
The generic_hwtstamp_ioctl_lower() function does not expect a NULL ifr and dereferences it, leading to a system crash.
Fix this by adding a NULL check for kernel_cfg->ifr in generic_hwtstamp_ioctl_lower(). If ifr is NULL, return -EINVAL.
Which versions are affected by CVE-2025-40255?
How do I fix CVE-2025-40255?
Apply the vendor's patch.
Is CVE-2025-40255 being exploited?
There is no known exploitation of CVE-2025-40255 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2025-40255, DEBIAN-CVE-2025-40255, GHSA-3mxh-p32w-7p56, UBUNTU-CVE-2025-40255.