CVE-2026-89639 cifs: use cifs_invalidate_cache() in cifs_do_truncate() for O_TRUNC
A race condition in the Linux kernel CIFS module allows serving stale cached data during file truncation, potentially leading to information disclosure.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89639?
CVE-2026-89639 is a high-severity vulnerability in Linux, published on 11 Sep 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
cifs: use cifs_invalidate_cache() in cifs_do_truncate() for O_TRUNC
cifs_do_truncate() is invoked from cifs_open() without i_rwsem, so it cannot use cifs_resize_file_locked() to perform a proper fscache cookie resize. Instead, add cifs_invalidate_cache() after cifs_setsize().
cifs_invalidate_cache() calls fscache_invalidate(), which works without holding i_rwsem: it unconditionally increments inval_counter and sets FSCACHE_COOKIE_NO_DATA_TO_READ, ensuring that stale cached data is not served once the cookie is later activated by fscache_use_cookie(). Truncation to zero leaves no valid cached data, making invalidation the correct semantic here.
Which versions are affected by CVE-2026-89639?
How do I fix CVE-2026-89639?
Apply the vendor's patch.
Is CVE-2026-89639 being exploited?
There is no known exploitation of CVE-2026-89639 in the wild and no public exploit code.
Sources
Also known as BELL-CVE-2026-89639, DEBIAN-CVE-2026-89639, GHSA-m6p4-6vjr-qq2h, UBUNTU-CVE-2026-89639.