CVE-2026-97939 ipmr: account multicast table and route memory
A privileged user in a network namespace can exhaust host memory by creating unaccounted multicast routing tables, causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-97939?
CVE-2026-97939 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:
ipmr: account multicast table and route memory
A netadmin in a user+net namespace can create many IPv4 and IPv6 multicast routing tables with MRT_TABLE and MRT6_TABLE. Each unseen id allocates an mr_table via the shared mr_table_alloc(), links it into the per-net list, and leaves it until netns teardown. Those objects were not charged to memcg, so the host unreclaimable slab grows with the table count.
Account mr_table allocations with GFP_KERNEL_ACCOUNT and mark the IPv4/IPv6 MFC caches SLAB_ACCOUNT. This matches the established handling of IP addresses, routes and alternate interface names.
Unresolved MFC entries are still allocated from softIRQ with GFP_ATOMIC and are not charged. They expire after 10 seconds and are bounded by the socket receive queue; see commit 0079ad8e8dc3 ("ipmr: remove hard code cache_resolve_queue_len limit").
Which versions are affected by CVE-2026-97939?
How do I fix CVE-2026-97939?
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-2026-97939 being exploited?
There is no known exploitation of CVE-2026-97939 in the wild and no public exploit code.
Sources
Also known as AZL-104625, BELL-CVE-2026-97939, DEBIAN-CVE-2026-97939, GHSA-9pw8-8xmv-73cr, UBUNTU-CVE-2026-97939.