CVE-2026-72321 ipv4: igmp: Fix potential memory leaks in igmp_mod_timer() and igmp_stop_timer()
A remote attacker can trigger a memory leak in the Linux kernel IGMP implementation, potentially leading to 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-2026-72321?
CVE-2026-72321 is a memory corruption 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:
ipv4: igmp: Fix potential memory leaks in igmp_mod_timer() and igmp_stop_timer()
When a timer is deleted and not re-armed in igmp_mod_timer(), or stopped in igmp_stop_timer(), the code currently decrements the reference counter of the multicast list entry @im using refcount_dec(&im->refcnt).
However, both functions can be called from the RCU reader path: - igmp_mod_timer() via igmp_heard_query() -> for_each_pmc_rcu() - igmp_stop_timer() via igmp_rcv() -> igmp_heard_report()
If the group im was concurrently removed from the list by ip_mc_dec_group(), its reference count might have already been decremented to 1.
In this case, timer_delete() succeeds, and refcount_dec() decrements the refcount from 1 to 0. Since refcount_dec() does not free the object when it hits 0 (unlike ip_ma_put()), the im structure is leaked.
Fix this by using ip_ma_put(im) instead of refcount_dec(&im->refcnt), and deferring the put until after the spinlock is released.
Which versions are affected by CVE-2026-72321?
How do I fix CVE-2026-72321?
Apply the vendor's patch.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-72321 being exploited?
There is no known exploitation of CVE-2026-72321 in the wild and no public exploit code.
Sources
Also known as AZL-96117, BELL-CVE-2026-72321, DEBIAN-CVE-2026-72321, GHSA-mrw5-54xq-r399, UBUNTU-CVE-2026-72321.