CVE-2026-31705 ksmbd: fix out-of-bounds write in smb2_get_ea() EA alignment
An out-of-bounds write in the Linux kernel's ksmbd module allows attackers to corrupt kernel memory, potentially leading to code execution or privilege escalation.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-31705?
CVE-2026-31705 is a critical memory corruption vulnerability in Linux kernel, published on 1 May 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
ksmbd: fix out-of-bounds write in smb2_get_ea() EA alignment
smb2_get_ea() applies 4-byte alignment padding via memset() after writing each EA entry. The bounds check on buf_free_len is performed before the value memcpy, but the alignment memset fires unconditionally afterward with no check on remaining space.
When the EA value exactly fills the remaining buffer (buf_free_len == 0 after value subtraction), the alignment memset writes 1-3 NUL bytes past the buf_free_len boundary. In compound requests where the response buffer is shared across commands, the first command (e.g., READ) can consume most of the buffer, leaving a tight remainder for the QUERY_INFO EA response. The alignment memset then overwrites past the physical kvmalloc allocation into adjacent kernel heap memory.
Add a bounds check before the alignment memset to ensure buf_free_len can accommodate the padding bytes.
This is the same bug pattern fixed by commit beef2634f81f ("ksmbd: fix potencial OOB in get_file_all_info() for compound requests") and commit fda9522ed6af ("ksmbd: fix OOB write in QUERY_INFO for compound requests"), both of which added bounds checks before unconditional writes in QUERY_INFO response handlers.
Weakness: CWE-787
Which versions are affected by CVE-2026-31705?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31705?
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-2026-31705 being exploited?
There is no known exploitation of CVE-2026-31705 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-31705, DEBIAN-CVE-2026-31705, GHSA-5jgf-2w89-7334, ROOT-OS-DEBIAN-12-CVE-2026-31705, ROOT-OS-UBUNTU-2204-CVE-2026-31705, ROOT-OS-UBUNTU-2404-CVE-2026-31705 and 1 more.