CVE-2026-43490 ksmbd: validate inherited ACE SID length
A memory corruption vulnerability in the Linux kernel's ksmbd SMB server allows attackers to execute code or cause denial of service via malformed ACEs.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-43490?
CVE-2026-43490 is a high-severity memory corruption vulnerability in Linux kernel, published on 15 May 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: validate inherited ACE SID length
smb_inherit_dacl() walks the parent directory DACL loaded from the security descriptor xattr. It verifies that each ACE contains the fixed SID header before using it, but does not verify that the variable-length SID described by sid.num_subauth is fully contained in the ACE.
A malformed inheritable ACE can advertise more subauthorities than are present in the ACE. compare_sids() may then read past the ACE. smb_set_ace() also clamps the copied destination SID, but used the unchecked source SID count to compute the inherited ACE size. That could advance the temporary inherited ACE buffer pointer and nt_size accounting past the allocated buffer.
Fix this by validating the parent ACE SID count and SID length before using the SID during inheritance. Compute the inherited ACE size from the copied SID so the size matches the bounded destination SID. Reject the inherited DACL if size accumulation would overflow smb_acl.size or the security descriptor allocation size.
Weakness: CWE-787
Which versions are affected by CVE-2026-43490?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-43490?
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-2026-43490 being exploited?
There is no known exploitation of CVE-2026-43490 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-43490, DEBIAN-CVE-2026-43490, GHSA-9hm7-v4rj-6wqj, ROOT-OS-DEBIAN-12-CVE-2026-43490, ROOT-OS-UBUNTU-2204-CVE-2026-43490, ROOT-OS-UBUNTU-2404-CVE-2026-43490 and 1 more.