CVE-2025-40268 cifs: client: fix memory leak in smb3_fs_context_parse_param

Not scored Published 6 Dec 2025 Updated 11 May 2026

A memory leak in the Linux kernel CIFS client allows local attackers to exhaust kernel memory, causing 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-2025-40268?

CVE-2025-40268 is a memory corruption vulnerability in Linux, published on 6 Dec 2025. 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:

cifs: client: fix memory leak in smb3_fs_context_parse_param

The user calls fsconfig twice, but when the program exits, free() only frees ctx->source for the second fsconfig, not the first. Regarding fc->source, there is no code in the fs context related to its memory reclamation.

To fix this memory leak, release the source memory corresponding to ctx or fc before each parsing.

syzbot reported: BUG: memory leak unreferenced object 0xffff888128afa360 (size 96): backtrace (crc 79c9c7ba): kstrdup+0x3c/0x80 mm/util.c:84 smb3_fs_context_parse_param+0x229b/0x36c0 fs/smb/client/fs_context.c:1444

BUG: memory leak unreferenced object 0xffff888112c7d900 (size 96): backtrace (crc 79c9c7ba): smb3_fs_context_fullpath+0x70/0x1b0 fs/smb/client/fs_context.c:629 smb3_fs_context_parse_param+0x2266/0x36c0 fs/smb/client/fs_context.c:1438

Which versions are affected by CVE-2025-40268?

How do I fix CVE-2025-40268?

Apply the vendor's patch.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2025-40268 being exploited?

There is no known exploitation of CVE-2025-40268 in the wild and no public exploit code.

Sources

Also known as BELL-CVE-2025-40268, DEBIAN-CVE-2025-40268, GHSA-cvhf-p6qw-wm2q, ROOT-OS-DEBIAN-12-CVE-2025-40268, ROOT-OS-DEBIAN-13-CVE-2025-40268, ROOT-OS-UBUNTU-2204-CVE-2025-40268 and 2 more.