CVE-2026-43405 libceph: Use u32 for non-negative values in ceph_monmap_decode()
A signedness error in the Linux kernel's Ceph client allows attackers to trigger unnecessary large memory allocations, potentially causing denial of service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-43405?
CVE-2026-43405 is a high-severity vulnerability in Linux kernel, published on 8 May 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: Use u32 for non-negative values in ceph_monmap_decode()
This patch fixes unnecessary implicit conversions that change signedness of blob_len and num_mon in ceph_monmap_decode(). Currently blob_len and num_mon are (signed) int variables. They are used to hold values that are always non-negative and get assigned in ceph_decode_32_safe(), which is meant to assign u32 values. Both variables are subsequently used as unsigned values, and the value of num_mon is further assigned to monmap->num_mon, which is of type u32. Therefore, both variables should be of type u32. This is especially relevant for num_mon. If the value read from the incoming message is very large, it is interpreted as a negative value, and the check for num_mon > CEPH_MAX_MON does not catch it. This leads to the attempt to allocate a very large chunk of memory for monmap, which will most likely fail. In this case, an unnecessary attempt to allocate memory is performed, and -ENOMEM is returned instead of -EINVAL.
Which versions are affected by CVE-2026-43405?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-43405?
Apply the vendor's patch.
Is CVE-2026-43405 being exploited?
There is no known exploitation of CVE-2026-43405 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-43405, DEBIAN-CVE-2026-43405, GHSA-5r63-pv2h-4jqg, ROOT-OS-DEBIAN-11-CVE-2026-43405, ROOT-OS-UBUNTU-2204-CVE-2026-43405, ROOT-OS-UBUNTU-2404-CVE-2026-43405 and 1 more.