Linux Kernel l2tp /proc/net/pppol2tp pppol2tp_proc_release/l2tp_dfs_seq_release tunnel/session use after free

Summaryinfo

A vulnerability was found in Linux Kernel. It has been declared as problematic. This impacts the function pppol2tp_proc_release/l2tp_dfs_seq_release of the file /proc/net/pppol2tp of the component l2tp. Executing a manipulation of the argument tunnel/session can lead to use after free. This vulnerability is registered as CVE-2026-74735. The attack needs to be launched locally. No exploit is available.

Detailsinfo

A vulnerability was found in Linux Kernel (version now known). It has been declared as problematic. This vulnerability affects the function pppol2tp_proc_release/l2tp_dfs_seq_release of the file /proc/net/pppol2tp of the component l2tp. The manipulation of the argument tunnel/session with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. As an impact it is known to affect integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at git.kernel.org. This vulnerability was named CVE-2026-74735 since 08/15/2026. The exploitation appears to be easy. The attack needs to be approached locally. There are known technical details, but no exploit is available. The current price for an exploit might be approx. USD $0-$5k (estimation calculated on 08/26/2026).

Applying the patch ebe2774e956482dd3c70b8991f6f7654356339e6 is able to eliminate this problem.

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Productinfo

Type

• Operating System

Vendor

• Linux

Name

• Kernel

License

• open-source

Website

• Vendor: https://www.kernel.org/

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