CVE-2026-43408 ceph: add a bunch of missing ceph_path_info initializers
Missing initializers in Ceph kernel code cause crashes and potential privilege escalation when freeing uninitialized path info structures.
- 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-2026-43408?
CVE-2026-43408 is a high-severity vulnerability in Linux kernel, published on 8 May 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:
ceph: add a bunch of missing ceph_path_info initializers
ceph_mdsc_build_path() must be called with a zero-initialized ceph_path_info parameter, or else the following ceph_mdsc_free_path_info() may crash.
Example crash (on Linux 6.18.12):
virt_to_cache: Object is not a Slab page! WARNING: CPU: 184 PID: 2871736 at mm/slub.c:6732 kmem_cache_free+0x316/0x400 [...] Call Trace: [...] ceph_open+0x13d/0x3e0 do_dentry_open+0x134/0x480 vfs_open+0x2a/0xe0 path_openat+0x9a3/0x1160 [...] cache_from_obj: Wrong slab cache. names_cache but object is from ceph_inode_info WARNING: CPU: 184 PID: 2871736 at mm/slub.c:6746 kmem_cache_free+0x2dd/0x400 [...] kernel BUG at mm/slub.c:634! Oops: invalid opcode: 0000 [#1] SMP NOPTI RIP: 0010:__slab_free+0x1a4/0x350
Some of the ceph_mdsc_build_path() callers had initializers, but others had not, even though they were all added by commit 15f519e9f883 ("ceph: fix race condition validating r_parent before applying state"). The ones without initializer are suspectible to random crashes. (I can imagine it could even be possible to exploit this bug to elevate privileges.)
Unfortunately, these Ceph functions are undocumented and its semantics can only be derived from the code. I see that ceph_mdsc_build_path() initializes the structure only on success, but not on error.
Calling ceph_mdsc_free_path_info() after a failed ceph_mdsc_build_path() call does not even make sense, but that's what all callers do, and for it to be safe, the structure must be zero-initialized. The least intrusive approach to fix this is therefore to add initializers everywhere.
Which versions are affected by CVE-2026-43408?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-43408?
Apply the vendor's patch.
Is CVE-2026-43408 being exploited?
There is no known exploitation of CVE-2026-43408 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-43408, DEBIAN-CVE-2026-43408, GHSA-97qv-cc94-mr6w, ROOT-OS-UBUNTU-2404-CVE-2026-43408, UBUNTU-CVE-2026-43408.