CVE-2026-68099 ksmbd: restore DACL size on check_add_overflow() to avoid malformed ACL
An integer overflow in ksmbd causes malformed ACLs, leading to out-of-bounds reads and potential denial of service or information disclosure.
- 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-2026-68099?
CVE-2026-68099 is a vulnerability in Linux, published on 10 Aug 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: restore DACL size on check_add_overflow() to avoid malformed ACL
check_add_overflow() unconditionally writes the truncated sum into *d even on overflow, per its contract in include/linux/overflow.h. The four check_add_overflow() guards in set_posix_acl_entries_dacl() and set_ntacl_dacl() break out of the ACE-building loops on overflow, but the truncated *size is then consumed downstream at the end of set_ntacl_dacl():
pndacl->size = cpu_to_le16(le16_to_cpu(pndacl->size) + size);
This produces an on-wire NT ACL whose pndacl->size under-reports the bytes actually written by the preceding fill_ace_for_sid()/memcpy() calls, yielding a malformed ACL that can trigger out-of-bounds reads when re-parsed by clients or ksmbd itself.
Restore *size to its pre-addition value on each overflow branch (via `*size -= ace_sz` / `size -= nt_ace_size`) so that after the break, *size once again holds the cumulative size of the successfully-written ACEs. The committed ACL is then truncated-but-self-consistent rather than malformed.
The ksmbd DACL builders are the only check_add_overflow() sites found where an overflow path breaks out of a loop and the destination value is consumed afterward. The other nearby break-style cases either return -EINVAL on overflow (transport_ipc.c) or break without consuming the overflowed destination value afterward (buildid.c).
Which versions are affected by CVE-2026-68099?
How do I fix CVE-2026-68099?
Apply the vendor's patch.
Is CVE-2026-68099 being exploited?
There is no known exploitation of CVE-2026-68099 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-68099, DEBIAN-CVE-2026-68099, GHSA-xjwm-2vhv-89mg, UBUNTU-CVE-2026-68099.