Bug 2468161 (CVE-2026-43405)

Summary: CVE-2026-43405 kernel: libceph: Use u32 for non-negative values in ceph_monmap_decode()
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Priority: medium    
Version: unspecifiedCC: rhel-process-autobot, watson-tool-maintainers
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OS: Linux   
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A flaw was found in the libceph component of the Linux kernel. This vulnerability occurs in the ceph_monmap_decode() function due to incorrect handling of non-negative values, where int variables are used instead of u32 for blob_len and num_mon. An attacker could exploit this by sending a specially crafted message with an excessively large num_mon value. This could lead to an attempt to allocate a very large amount of memory, resulting in a Denial of Service (DoS) condition.
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Description OSIDB Bzimport 2026-05-08 15:02:23 UTC 
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.
Comment 1 Keith Grant 2026-05-08 22:21:35 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2026050841-CVE-2026-43405-38d6@gregkh/T