CVE-2026-72322 ipv6: mcast: Fix potential UAF in MLD delayed work
A race condition in Linux kernel IPv6 multicast handling allows a use-after-free, leading to a kernel panic and denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-72322?
CVE-2026-72322 is a critical use after free vulnerability in Linux, published on 15 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ipv6: mcast: Fix potential UAF in MLD delayed work
A race condition exists between device teardown and incoming MLD query processing, leading to a Use-After-Free in the MLD delayed work.
During device destruction, the primary reference to inet6_dev is dropped, which can drop its refcount to 0. The actual freeing of inet6_dev memory is deferred via RCU.
Concurrently, the packet receive path runs under RCU read lock and obtains the inet6_dev pointer. Because the memory is RCU-protected, CPU-0 can safely dereference inet6_dev even if its refcount has hit 0.
However, if CPU-0 calls igmp6_event_query() and schedules delayed work, it attempts to acquire a reference using in6_dev_hold(). This increments the refcount from 0 to 1, triggering a "refcount_t: addition on 0" warning. Since the inet6_dev memory is still scheduled to be freed after the RCU grace period, the device is freed while the work is still scheduled. When the work runs, it accesses the freed memory, causing a kernel panic.
Fix this by using refcount_inc_not_zero() (via a new helper in6_dev_hold_safe()) to prevent acquiring a reference if the device is already being destroyed. If the refcount is 0, we do not schedule the work.
Which versions are affected by CVE-2026-72322?
How do I fix CVE-2026-72322?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-72322 being exploited?
There is no known exploitation of CVE-2026-72322 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-72322, DEBIAN-CVE-2026-72322, GHSA-p5wq-w75h-848c, UBUNTU-CVE-2026-72322.