CVE-2026-31704 ksmbd: use check_add_overflow() to prevent u16 DACL size overflow
An integer overflow in the Linux kernel's ksmbd module allows buffer corruption via crafted ACL entries, potentially leading to code execution or privilege escalation.
- 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-2026-31704?
CVE-2026-31704 is a medium-severity vulnerability in Linux kernel, published on 1 May 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:
ksmbd: use check_add_overflow() to prevent u16 DACL size overflow
set_posix_acl_entries_dacl() and set_ntacl_dacl() accumulate ACE sizes in u16 variables. When a file has many POSIX ACL entries, the accumulated size can wrap past 65535, causing the pointer arithmetic (char *)pndace + *size to land within already-written ACEs. Subsequent writes then overwrite earlier entries, and pndacl->size gets a truncated value.
Use check_add_overflow() at each accumulation point to detect the wrap before it corrupts the buffer, consistent with existing check_mul_overflow() usage elsewhere in smbacl.c.
Which versions are affected by CVE-2026-31704?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31704?
Apply the vendor's patch.
Is CVE-2026-31704 being exploited?
There is no known exploitation of CVE-2026-31704 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-31704, DEBIAN-CVE-2026-31704, GHSA-xmgr-rx43-m3gf, ROOT-OS-DEBIAN-12-CVE-2026-31704, ROOT-OS-UBUNTU-2204-CVE-2026-31704, ROOT-OS-UBUNTU-2404-CVE-2026-31704 and 1 more.