CVE-2025-21648 netfilter: conntrack: clamp maximum hashtable size to INT_MAX
A flaw in the Linux kernel netfilter conntrack module allows a local attacker to trigger a kernel warning and potential denial of service by resizing the hashtable.
- 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-2025-21648?
CVE-2025-21648 is a medium-severity denial of service vulnerability in Linux kernel, published on 19 Jan 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:
netfilter: conntrack: clamp maximum hashtable size to INT_MAX
Use INT_MAX as maximum size for the conntrack hashtable. Otherwise, it is possible to hit WARN_ON_ONCE in __kvmalloc_node_noprof() when resizing hashtable because __GFP_NOWARN is unset. See:
0708a0afe291 ("mm: Consider __GFP_NOWARN flag for oversized kvmalloc() calls")
Note: hashtable resize is only possible from init_netns.
Which versions are affected by CVE-2025-21648?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2025-21648?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-21648 being exploited?
There is no known exploitation of CVE-2025-21648 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2025-21648, DEBIAN-CVE-2025-21648, GHSA-w9f5-vpqq-grqj, UBUNTU-CVE-2025-21648.