# 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.

- **Severity:** Not scored
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Aug 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-96117, BELL-CVE-2026-72321, DEBIAN-CVE-2026-72321, GHSA-mrw5-54xq-r399, UBUNTU-CVE-2026-72321

## 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.

## Is CVE-2026-72321 being exploited?

There is no known exploitation of CVE-2026-72321 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-72321 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-72321 in the wild and no public exploit code.

Affected product: Linux. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-72321/ (Markdown: https://insights.sbomify.com/CVE-2026-72321/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-72321
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-72321
- OSV: https://osv.dev/vulnerability/CVE-2026-72321

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-72321/
Summaries are generated and may contain mistakes; the official description above is the record.