# CVE-2026-74609: tipc: read le->link under the node lock in tipc_node_link_down()

> A race condition in the Linux kernel TIPC module allows attackers to trigger a use-after-free, potentially leading to code execution or system crashes.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** Yes
- **Published:** 22 Aug 2026
- **Updated:** 16 Oct 2026
- **Also known as:** AZL-97062, BELL-CVE-2026-74609, DEBIAN-CVE-2026-74609, GHSA-c6xm-fh9c-399h, UBUNTU-CVE-2026-74609

## What is CVE-2026-74609?

CVE-2026-74609 is a high-severity use after free vulnerability in Linux, published on 22 Aug 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:

tipc: read le->link under the node lock in tipc_node_link_down()

tipc_node_link_down() caches the link pointer before taking n->lock:

	struct tipc_link *l = le->link;		/* unlocked */

	if (!l)
		return;
	tipc_node_write_lock(n);
	if (!tipc_link_is_establishing(l)) {	/* deref l */
	...
		tipc_link_reset(l);		/* write into l */
	if (delete) {
		kfree(l);
		le->link = NULL;

The delete=true caller frees that very object under n->lock, so the lock
does not protect the cached pointer against it:

 - CPU A, delete=false: tipc_rcv() on TIPC_LINK_DOWN_EVT, or the link
   supervision timer via tipc_node_timeout(), reads l unlocked and then
   dereferences it under n->lock;
 - CPU B, delete=true: netlink TIPC_NL_BEARER_DISABLE -> bearer_disable()
   -> tipc_node_delete_links() -> tipc_node_link_down(n, bearer_id, true)
   -> kfree(l).

The link is freed with plain kfree(), not kfree_rcu(), and for UDP bearers
disable_media() only schedules the asynchronous cleanup_bearer() work, so
its synchronize_net() runs after the links are already gone.  An in-flight
CPU A that has read l therefore dereferences freed memory once B frees it:
a use-after-free read in tipc_link_is_establishing(), and a use-after-free
write via tipc_link_reset() on the establishing branch.

The following trace was captured on 7.2.0-rc5-00284-gaf39eb111ce6:

  BUG: KASAN: slab-use-after-free in tipc_link_is_establishing (net/tipc/link.c:285)
  Read of size 4 at addr ffff88802e2aa068 by task swapper/2/0
   tipc_link_is_establishing (net/tipc/link.c:285)
   tipc_node_link_down (net/tipc/node.c:1076)
   tipc_node_timeout (net/tipc/node.c:843)
  Allocated by task 9549:
   tipc_link_create (net/tipc/link.c:490)
   tipc_node_check_dest (net/tipc/node.c:1279)
   tipc_disc_rcv (net/tipc/discover.c:252)
   tipc_udp_recv (net/tipc/udp_media.c:389)
  Freed by task 9549:
   tipc_node_link_down (net/tipc/node.c:1084)
   tipc_node_delete_links (net/tipc/node.c:1320)
   bearer_disable (net/tipc/bearer.c:414)
   __tipc_nl_bearer_disable (net/tipc/bearer.c:992)

Move the le->link read inside tipc_node_write_lock(), so it is serialised
against the kfree() in the delete path.  A racing teardown now either has
not run yet, and we see a valid link, or has already run, and we see NULL.

## Which versions are affected by CVE-2026-74609?


## How do I fix CVE-2026-74609?

Apply the vendor's patch.

## Is CVE-2026-74609 being exploited?

There is no known exploitation of CVE-2026-74609 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74609 and fix it if it is affected.

What it is: CVE-2026-74609 is a high-severity use after free vulnerability in Linux, published on 22 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-74609 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-2026-74609/ (Markdown: https://insights.sbomify.com/CVE-2026-74609/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74609
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74609
- OSV: https://osv.dev/vulnerability/CVE-2026-74609

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74609/
Summaries are generated and may contain mistakes; the official description above is the record.