CVE-2025-39838 cifs: prevent NULL pointer dereference in UTF16 conversion

What is CVE-2025-39838?

CVE-2025-39838 is a medium-severity vulnerability in Debian Debian Linux, published on 19 Sep 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: prevent NULL pointer dereference in UTF16 conversion

There can be a NULL pointer dereference bug here. NULL is passed to __cifs_sfu_make_node without checks, which passes it unchecked to cifs_strndup_to_utf16, which in turn passes it to cifs_local_to_utf16_bytes where '*from' is dereferenced, causing a crash.

This patch adds a check for NULL 'src' in cifs_strndup_to_utf16 and returns NULL early to prevent dereferencing NULL pointer.

Found by Linux Verification Center (linuxtesting.org) with SVACE

Weakness: CWE-476

Which versions are affected by CVE-2025-39838?

It affects 2 products.

Products include Debian Debian Linux, Linux kernel.

How do I fix CVE-2025-39838?

Apply the vendor's patch.

Is CVE-2025-39838 being exploited?

There is no known exploitation of CVE-2025-39838 in the wild and no public exploit code.

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All Debian Debian Linux vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-67596, BELL-CVE-2025-39838, DEBIAN-CVE-2025-39838, GHSA-9q78-c4fv-64q9, ROOT-OS-DEBIAN-11-CVE-2025-39838, ROOT-OS-DEBIAN-12-CVE-2025-39838 and 4 more.