CVE-2026-89657 libceph: validate OSD extent maps before cursor advance
A malicious Ceph OSD peer can crash the Linux kernel client by sending malformed sparse-read replies that trigger an assertion failure.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-89657?
CVE-2026-89657 is a high-severity denial of service 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:
libceph: validate OSD extent maps before cursor advance
net/ceph/osd_client.c:osd_sparse_read() validates that the sparse-read data length matches the summed extent lengths, but it does not validate that each OSD-supplied extent is monotonic and lies inside the original request range. A malformed authenticated OSD reply can advertise a far-forward nonzero extent offset with a matching data length and make the client advance the message-data cursor beyond the request buffer. This reaches the BUG_ON(!*length) assertion in ceph_msg_data_next() from the client receive path.
Impact: A malicious or compromised authenticated Ceph OSD peer can crash a kernel Ceph client via a malformed sparse-read reply.
Reject sparse extent maps that overflow, move backwards, overlap, or extend outside the original sparse-read request before advancing the cursor.
[ idryomov: perform sparse_extent_map_valid() check a bit earlier, in CEPH_SPARSE_READ_DATA_LEN instead of CEPH_SPARSE_READ_DATA_PRE state ]
Which versions are affected by CVE-2026-89657?
How do I fix CVE-2026-89657?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-89657 being exploited?
There is no known exploitation of CVE-2026-89657 in the wild and no public exploit code.
Sources
Also known as AZL-100554, BELL-CVE-2026-89657, DEBIAN-CVE-2026-89657, GHSA-9478-77xp-cr7g, UBUNTU-CVE-2026-89657.