CVE-2026-97598 ipv4: fib: bound automatic table ID allocation
A local attacker can cause a denial of service in the Linux kernel by exhausting routing table IDs, leading to excessive CPU usage while holding the RTNL lock.
- 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-2026-97598?
CVE-2026-97598 is a denial of service vulnerability in Linux, published on 25 Sep 2026. 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:
ipv4: fib: bound automatic table ID allocation
fib_empty_table() probes every table ID from 1 until it finds a free one. IPv4 tables are stored in a 256-bucket hash table, so a dense set of IDs makes each probe walk a growing hash chain while RTNL is held.
Automatic table assignment ("ip rule ... table 0") is an IPv4-only legacy path. Bound the automatically allocated ID to 4096 so the RTNL hold stays bounded, without changing lookups of explicitly specified table IDs.
This changes user-visible behavior. A table-0 rule previously received the lowest free ID in 1..RT_TABLE_MAX (0xFFFFFFFF). After this patch the search stops at 4096 and the rule add fails with ENOBUFS if that range is fully occupied. Explicit table IDs above 4096 remain usable.
The automatic path is unused in practice: it is IPv4-only, not documented by ip-rule, uncovered by kernel selftests, and both NetworkManager and systemd refuse table 0.
Which versions are affected by CVE-2026-97598?
How do I fix CVE-2026-97598?
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-2026-97598 being exploited?
There is no known exploitation of CVE-2026-97598 in the wild and no public exploit code.
Sources
Also known as AZL-104415, BELL-CVE-2026-97598, DEBIAN-CVE-2026-97598, GHSA-9pxv-wwmf-9jpr, UBUNTU-CVE-2026-97598.