# CVE-2026-43407: libceph: Fix potential out-of-bounds access in ceph_handle_auth_reply()

> An integer overflow in the Linux kernel's libceph module allows out-of-bounds memory access, potentially leading to crashes or code execution.

- **Severity:** Critical 9.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 8 May 2026
- **Updated:** 19 Oct 2026
- **Also known as:** BELL-CVE-2026-43407, DEBIAN-CVE-2026-43407, GHSA-g5m7-8jmr-xx94, ROOT-OS-DEBIAN-11-CVE-2026-43407, ROOT-OS-UBUNTU-2204-CVE-2026-43407, ROOT-OS-UBUNTU-2404-CVE-2026-43407, UBUNTU-CVE-2026-43407

## What is CVE-2026-43407?

CVE-2026-43407 is a critical 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: Fix potential out-of-bounds access in ceph_handle_auth_reply()

This patch fixes an out-of-bounds access in ceph_handle_auth_reply()
that can be triggered by a message of type CEPH_MSG_AUTH_REPLY. In
ceph_handle_auth_reply(), the value of the payload_len field of such a
message is stored in a variable of type int. A value greater than
INT_MAX leads to an integer overflow and is interpreted as a negative
value. This leads to decrementing the pointer address by this value and
subsequently accessing it because ceph_decode_need() only checks that
the memory access does not exceed the end address of the allocation.

This patch fixes the issue by changing the data type of payload_len to
u32. Additionally, the data type of result_msg_len is changed to u32,
as it is also a variable holding a non-negative length.

Also, an additional layer of sanity checks is introduced, ensuring that
directly after reading it from the message, payload_len and
result_msg_len are not greater than the overall segment length.

BUG: KASAN: slab-out-of-bounds in ceph_handle_auth_reply+0x642/0x7a0 [libceph]
Read of size 4 at addr ffff88811404df14 by task kworker/20:1/262

CPU: 20 UID: 0 PID: 262 Comm: kworker/20:1 Not tainted 6.19.2 #5 PREEMPT(voluntary)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
Workqueue: ceph-msgr ceph_con_workfn [libceph]
Call Trace:
 <TASK>
 dump_stack_lvl+0x76/0xa0
 print_report+0xd1/0x620
 ? __pfx__raw_spin_lock_irqsave+0x10/0x10
 ? kasan_complete_mode_report_info+0x72/0x210
 kasan_report+0xe7/0x130
 ? ceph_handle_auth_reply+0x642/0x7a0 [libceph]
 ? ceph_handle_auth_reply+0x642/0x7a0 [libceph]
 __asan_report_load_n_noabort+0xf/0x20
 ceph_handle_auth_reply+0x642/0x7a0 [libceph]
 mon_dispatch+0x973/0x23d0 [libceph]
 ? apparmor_socket_recvmsg+0x6b/0xa0
 ? __pfx_mon_dispatch+0x10/0x10 [libceph]
 ? __kasan_check_write+0x14/0x30i
 ? mutex_unlock+0x7f/0xd0
 ? __pfx_mutex_unlock+0x10/0x10
 ? __pfx_do_recvmsg+0x10/0x10 [libceph]
 ceph_con_process_message+0x1f1/0x650 [libceph]
 process_message+0x1e/0x450 [libceph]
 ceph_con_v2_try_read+0x2e48/0x6c80 [libceph]
 ? __pfx_ceph_con_v2_try_read+0x10/0x10 [libceph]
 ? save_fpregs_to_fpstate+0xb0/0x230
 ? raw_spin_rq_unlock+0x17/0xa0
 ? finish_task_switch.isra.0+0x13b/0x760
 ? __switch_to+0x385/0xda0
 ? __kasan_check_write+0x14/0x30
 ? mutex_lock+0x8d/0xe0
 ? __pfx_mutex_lock+0x10/0x10
 ceph_con_workfn+0x248/0x10c0 [libceph]
 process_one_work+0x629/0xf80
 ? __kasan_check_write+0x14/0x30
 worker_thread+0x87f/0x1570
 ? __pfx__raw_spin_lock_irqsave+0x10/0x10
 ? __pfx_try_to_wake_up+0x10/0x10
 ? kasan_print_address_stack_frame+0x1f7/0x280
 ? __pfx_worker_thread+0x10/0x10
 kthread+0x396/0x830
 ? __pfx__raw_spin_lock_irq+0x10/0x10
 ? __pfx_kthread+0x10/0x10
 ? __kasan_check_write+0x14/0x30
 ? recalc_sigpending+0x180/0x210
 ? __pfx_kthread+0x10/0x10
 ret_from_fork+0x3f7/0x610
 ? __pfx_ret_from_fork+0x10/0x10
 ? __switch_to+0x385/0xda0
 ? __pfx_kthread+0x10/0x10
 ret_from_fork_asm+0x1a/0x30
 </TASK>

[ idryomov: replace if statements with ceph_decode_need() for
  payload_len and result_msg_len ]

Weakness: CWE-125 (Out-of-bounds Read), CWE-190 (Integer Overflow or Wraparound)

## Which versions are affected by CVE-2026-43407?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-43407?

Apply the vendor's patch.

## Is CVE-2026-43407 being exploited?

There is no known exploitation of CVE-2026-43407 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-43407 and fix it if it is affected.

What it is: CVE-2026-43407 is a critical 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.
Exploitation: There is no known exploitation of CVE-2026-43407 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-43407/ (Markdown: https://insights.sbomify.com/CVE-2026-43407/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43407
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43407
- OSV: https://osv.dev/vulnerability/CVE-2026-43407

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43407/
Summaries are generated and may contain mistakes; the official description above is the record.