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.
- 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
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.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-74735 being exploited?
There is no known exploitation of CVE-2026-74735 in the wild and no public exploit code.
Sources
Also known as AZL-97743, BELL-CVE-2026-74735, DEBIAN-CVE-2026-74735, GHSA-wf96-m5fp-jh8c, UBUNTU-CVE-2026-74735.