CVE-2026-89634 smb: client: fix ALIGN() overflow in symlink_data() error context loop
An integer overflow in the Linux kernel SMB client allows attackers to bypass bounds checks, potentially causing infinite loops or out-of-bounds reads.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89634?
CVE-2026-89634 is a critical 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 ALIGN() overflow in symlink_data() error context loop
The check added by commit 7d9a7f1f96cd ("smb/client: fix possible infinite loop and oob read in symlink_data()") compared the post-ALIGN length against the remaining buffer, but ALIGN() itself can overflow: for ErrorDataLength near UINT32_MAX (e.g. 0xFFFFFFF9), ALIGN(x, 8) wraps to 0, so the subsequent bounds check passes, and the loop advances by zero bytes leaving 'p' pointing into stale data.
Fix by checking the raw ErrorDataLength against the remaining space before applying ALIGN(), then checking again after. Since raw_len is bounded by the buffer, raw_len + 7 cannot overflow, so the second check is an exact post-alignment bounds guard.
Which versions are affected by CVE-2026-89634?
How do I fix CVE-2026-89634?
Apply the vendor's patch.
Is CVE-2026-89634 being exploited?
There is no known exploitation of CVE-2026-89634 in the wild and no public exploit code.
Sources
Also known as AZL-100628, BELL-CVE-2026-89634, DEBIAN-CVE-2026-89634, GHSA-959h-4fxq-gqhj, UBUNTU-CVE-2026-89634.