# CVE-2026-74735: l2tp: fix tunnel and session refcount leak on seq_file release

> A local attacker can cause a reference count leak in the Linux kernel L2TP module by prematurely closing proc or debug files, leading to resource exhaustion and denial of service.

- **Severity:** Not scored
- **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:** 26 Aug 2026
- **Updated:** 21 Oct 2026
- **Also known as:** AZL-97743, BELL-CVE-2026-74735, DEBIAN-CVE-2026-74735, GHSA-wf96-m5fp-jh8c, UBUNTU-CVE-2026-74735

## What is CVE-2026-74735?

CVE-2026-74735 is a denial of service vulnerability in Linux, published on 26 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:

l2tp: fix tunnel and session refcount leak on seq_file release

In pppol2tp_proc_open() and l2tp_dfs_seq_open(), iteration state
(pd->tunnel and pd->session) is kept in seq_file private data to allow
iteration across multiple read() system calls.

However, if userspace closes /proc/net/pppol2tp or /sys/kernel/debug/l2tp/tunnels
before reading to end-of-file (EOF), any tunnel or session reference stored in
pd->tunnel / pd->session is left un-dropped when seq_file private data is freed.

Fix this by dropping any remaining pd->tunnel and pd->session references in
pppol2tp_proc_release() and l2tp_dfs_seq_release() when closing the file.

## Which versions are affected by CVE-2026-74735?


## How do I fix CVE-2026-74735?

Apply the vendor's patch.

## Is CVE-2026-74735 being exploited?

There is no known exploitation of CVE-2026-74735 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-74735 and fix it if it is affected.

What it is: CVE-2026-74735 is a denial of service vulnerability in Linux, published on 26 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-2026-74735 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-2026-74735/ (Markdown: https://insights.sbomify.com/CVE-2026-74735/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-74735
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-74735
- OSV: https://osv.dev/vulnerability/CVE-2026-74735

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-74735/
Summaries are generated and may contain mistakes; the official description above is the record.