CVE-2026-89632 smb: client: fix use-before-check of ReparseDataLength in reparse_buf_ptr()
A malicious SMB server can cause a kernel crash by sending a small response, leading to a use-before-check vulnerability in the Linux kernel SMB client.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89632?
CVE-2026-89632 is a high-severity vulnerability in Linux, published on 11 Sep 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:
smb: client: fix use-before-check of ReparseDataLength in reparse_buf_ptr()
reparse_buf_ptr() reads buf->ReparseDataLength before checking that count covers the full fixed header:
buf = (struct reparse_data_buffer *)((u8 *)io + off); len = sizeof(*buf); /* 8 bytes */ rdlen = le16_to_cpu(buf->ReparseDataLength); /* offset 4, 2 bytes */
if (count < len || count < rdlen + len) /* check comes after */
struct reparse_data_buffer has ReparseDataLength at offset 4. If a server returns OutputCount < 6, the read at offset 4-5 reaches past the end of the received data. The off+count bounds against iov_len were already validated, but that does not protect against count being smaller than sizeof(*buf).
Split the check: verify count >= sizeof(*buf) before reading ReparseDataLength, then verify count covers the data region.
Which versions are affected by CVE-2026-89632?
How do I fix CVE-2026-89632?
Apply the vendor's patch.
Is CVE-2026-89632 being exploited?
There is no known exploitation of CVE-2026-89632 in the wild and no public exploit code.
Sources
Also known as AZL-100757, BELL-CVE-2026-89632, DEBIAN-CVE-2026-89632, GHSA-j6wx-7c3w-595c, UBUNTU-CVE-2026-89632.