# CVE-2026-52961: ceph: fix BUG_ON in __ceph_build_xattrs_blob() due to stale blob size

> A stale blob size in the Ceph filesystem driver causes a kernel BUG_ON crash, leading to a denial of service.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 24 Jun 2026
- **Updated:** 14 Sep 2026
- **Also known as:** AZL-90717, BELL-CVE-2026-52961, DEBIAN-CVE-2026-52961, GHSA-7c47-vxfh-p7q4, ROOT-OS-DEBIAN-12-CVE-2026-52961, ROOT-OS-UBUNTU-2404-CVE-2026-52961, UBUNTU-CVE-2026-52961

## What is CVE-2026-52961?

CVE-2026-52961 is a medium-severity denial of service vulnerability in Linux kernel, published on 24 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

ceph: fix BUG_ON in __ceph_build_xattrs_blob() due to stale blob size

The generic/642 test-case can reproduce the kernel crash:

[40243.605254] ------------[ cut here ]------------
[40243.605956] kernel BUG at fs/ceph/xattr.c:918!
[40243.607142] Oops: invalid opcode: 0000 [#1] SMP PTI
[40243.608067] CPU: 7 UID: 0 PID: 498762 Comm: kworker/7:1 Not tainted 7.0.0-rc7+ #3 PREEMPT(full)
[40243.609700] Hardware name: QEMU Ubuntu 25.10 PC v2 (i440FX + PIIX, + 10.1 machine, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
[40243.611820] Workqueue: ceph-msgr ceph_con_workfn
[40243.612715] RIP: 0010:__ceph_build_xattrs_blob+0x1b8/0x1e0
[40243.613731] Code: 0f 84 82 fe ff ff e9 cf 8e 56 ff 48 8d 65 e8 31 c0 5b 41 5c 41 5d 5d 31 d2 31 c9 31 f6 31 ff 45 31 c0 45 31 c9 c3 cc cc cc cc <0f> 0b 4c 8b 62 08 41 8b 85 24 07 00 00 49 83 c4 04 41 89 44 24 fc
[40243.616888] RSP: 0018:ffffcc80c4d4b688 EFLAGS: 00010287
[40243.617773] RAX: 0000000000010026 RBX: 0000000000000001 RCX: 0000000000000000
[40243.618928] RDX: ffff8a773798dee0 RSI: 0000000000000000 RDI: 0000000000000000
[40243.620158] RBP: ffffcc80c4d4b6a0 R08: 0000000000000000 R09: 0000000000000000
[40243.621573] R10: 0000000000000000 R11: 0000000000000000 R12: ffff8a75f3b58000
[40243.622907] R13: ffff8a75f3b58000 R14: 0000000000000080 R15: 000000000000bffd
[40243.624054] FS:  0000000000000000(0000) GS:ffff8a787d1b4000(0000) knlGS:0000000000000000
[40243.625331] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[40243.626269] CR2: 000072f390b623c0 CR3: 000000011c02a003 CR4: 0000000000372ef0
[40243.627408] Call Trace:
[40243.627839]  <TASK>
[40243.628188]  __prep_cap+0x3fd/0x4a0
[40243.628789]  ? do_raw_spin_unlock+0x4e/0xe0
[40243.629474]  ceph_check_caps+0x46a/0xc80
[40243.630094]  ? __lock_acquire+0x4a2/0x2650
[40243.630773]  ? find_held_lock+0x31/0x90
[40243.631347]  ? handle_cap_grant+0x79f/0x1060
[40243.632068]  ? lock_release+0xd9/0x300
[40243.632696]  ? __mutex_unlock_slowpath+0x3e/0x340
[40243.633429]  ? lock_release+0xd9/0x300
[40243.634052]  handle_cap_grant+0xcf6/0x1060
[40243.634745]  ceph_handle_caps+0x122b/0x2110
[40243.635415]  mds_dispatch+0x5bd/0x2160
[40243.636034]  ? ceph_con_process_message+0x65/0x190
[40243.636828]  ? lock_release+0xd9/0x300
[40243.637431]  ceph_con_process_message+0x7a/0x190
[40243.638184]  ? kfree+0x311/0x4f0
[40243.638749]  ? kfree+0x311/0x4f0
[40243.639268]  process_message+0x16/0x1a0
[40243.639915]  ? sg_free_table+0x39/0x90
[40243.640572]  ceph_con_v2_try_read+0xf58/0x2120
[40243.641255]  ? lock_acquire+0xc8/0x300
[40243.641863]  ceph_con_workfn+0x151/0x820
[40243.642493]  process_one_work+0x22f/0x630
[40243.643093]  ? process_one_work+0x254/0x630
[40243.643770]  worker_thread+0x1e2/0x400
[40243.644332]  ? __pfx_worker_thread+0x10/0x10
[40243.645020]  kthread+0x109/0x140
[40243.645560]  ? __pfx_kthread+0x10/0x10
[40243.646125]  ret_from_fork+0x3f8/0x480
[40243.646752]  ? __pfx_kthread+0x10/0x10
[40243.647316]  ? __pfx_kthread+0x10/0x10
[40243.647919]  ret_from_fork_asm+0x1a/0x30
[40243.648556]  </TASK>
[40243.648902] Modules linked in: overlay hctr2 libpolyval chacha libchacha adiantum libnh libpoly1305 essiv intel_rapl_msr intel_rapl_common intel_uncore_frequency_common skx_edac_common nfit kvm_intel kvm irqbypass joydev ghash_clmulni_intel aesni_intel rapl input_leds mac_hid psmouse vga16fb serio_raw vgastate floppy i2c_piix4 pata_acpi bochs qemu_fw_cfg i2c_smbus sch_fq_codel rbd dm_crypt msr parport_pc ppdev lp parport efi_pstore
[40243.654766] ---[ end trace 0000000000000000 ]---

Commit d93231a6bc8a ("ceph: prevent a client from exceeding the MDS
maximum xattr size") moved the required_blob_size computation to before
the __build_xattrs() call, introducing a race.

__build_xattrs() releases and reacquires i_ceph_lock during execution.
In that window, handle_cap_grant() may update i_xattrs.blob with a
newer MDS-provided blob and bump i_xattrs.version.  When
__bui
---truncated---

Weakness: CWE-617 (Reachable Assertion)

## Which versions are affected by CVE-2026-52961?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-52961?

Apply the vendor's patch.

## Is CVE-2026-52961 being exploited?

There is no known exploitation of CVE-2026-52961 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-2026-52961 and fix it if it is affected.

What it is: CVE-2026-52961 is a medium-severity denial of service vulnerability in Linux kernel, published on 24 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-52961 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-2026-52961/ (Markdown: https://insights.sbomify.com/CVE-2026-52961/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-52961
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-52961
- OSV: https://osv.dev/vulnerability/CVE-2026-52961

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-52961/
Summaries are generated and may contain mistakes; the official description above is the record.