CVE-2026-98171 smb: client: fix next_buffer UAF and NextCommand bounds in compound PDUs
A use-after-free and bounds checking flaw in the Linux kernel SMB client allows attackers to execute code or cause denial of service via crafted compound PDUs.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2026-98171?
CVE-2026-98171 is a high-severity use after free vulnerability in Linux, published on 6 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
In the Linux kernel, the following vulnerability has been resolved:
smb: client: fix next_buffer UAF and NextCommand bounds in compound PDUs
Fix several related bounds checking and pointer lifecycle issues in receive_encrypted_standard()'s handling of compound encrypted frames:
- Clear next_buffer after assigning it to server->bigbuf. A stale next_buffer pointer can lead to a use-after-free on subsequent error paths. - Update pdu_length to the decrypted plaintext size (buf_size). Using the pre-decryption length allows NextCommand to point into stale ciphertext residue. - Reject next_cmd values smaller than MID_HEADER_SIZE(server). - Fix an integer overflow in the upper bound check by verifying pdu_length - next_cmd < MID_HEADER_SIZE(server), ensuring the trailing slice is large enough for a header.
Which versions are affected by CVE-2026-98171?
How do I fix CVE-2026-98171?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-98171 being exploited?
There is no known exploitation of CVE-2026-98171 in the wild and no public exploit code.
Sources
Also known as AZL-106215, BELL-CVE-2026-98171, DEBIAN-CVE-2026-98171, GHSA-68gh-wq6f-89rf, UBUNTU-CVE-2026-98171.