# CVE-2023-52856: drm/bridge: lt8912b: Fix crash on bridge detach

> A null pointer dereference in the Linux kernel's lt8912b bridge driver causes a system crash during bridge detach operations.

- **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:** 21 May 2024
- **Updated:** 11 May 2026
- **Also known as:** BELL-CVE-2023-52856, DEBIAN-CVE-2023-52856, GHSA-3qr9-g9f2-22xh, UBUNTU-CVE-2023-52856

## What is CVE-2023-52856?

CVE-2023-52856 is a medium-severity vulnerability in Linux kernel, published on 21 May 2024. 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:

drm/bridge: lt8912b: Fix crash on bridge detach

The lt8912b driver, in its bridge detach function, calls
drm_connector_unregister() and drm_connector_cleanup().

drm_connector_unregister() should be called only for connectors
explicitly registered with drm_connector_register(), which is not the
case in lt8912b.

The driver's drm_connector_funcs.destroy hook is set to
drm_connector_cleanup().

Thus the driver should not call either drm_connector_unregister() nor
drm_connector_cleanup() in its lt8912_bridge_detach(), as they cause a
crash on bridge detach:

Unable to handle kernel NULL pointer dereference at virtual address 0000000000000000
Mem abort info:
  ESR = 0x0000000096000006
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x06: level 2 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000006, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=00000000858f3000
[0000000000000000] pgd=0800000085918003, p4d=0800000085918003, pud=0800000085431003, pmd=0000000000000000
Internal error: Oops: 0000000096000006 [#1] PREEMPT SMP
Modules linked in: tidss(-) display_connector lontium_lt8912b tc358768 panel_lvds panel_simple drm_dma_helper drm_kms_helper drm drm_panel_orientation_quirks
CPU: 3 PID: 462 Comm: rmmod Tainted: G        W          6.5.0-rc2+ #2
Hardware name: Toradex Verdin AM62 on Verdin Development Board (DT)
pstate: 80000005 (Nzcv daif -PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : drm_connector_cleanup+0x78/0x2d4 [drm]
lr : lt8912_bridge_detach+0x54/0x6c [lontium_lt8912b]
sp : ffff800082ed3a90
x29: ffff800082ed3a90 x28: ffff0000040c1940 x27: 0000000000000000
x26: 0000000000000000 x25: dead000000000122 x24: dead000000000122
x23: dead000000000100 x22: ffff000003fb6388 x21: 0000000000000000
x20: 0000000000000000 x19: ffff000003fb6260 x18: fffffffffffe56e8
x17: 0000000000000000 x16: 0010000000000000 x15: 0000000000000038
x14: 0000000000000000 x13: ffff800081914b48 x12: 000000000000040e
x11: 000000000000015a x10: ffff80008196ebb8 x9 : ffff800081914b48
x8 : 00000000ffffefff x7 : ffff0000040c1940 x6 : ffff80007aa649d0
x5 : 0000000000000000 x4 : 0000000000000001 x3 : ffff80008159e008
x2 : 0000000000000000 x1 : 0000000000000000 x0 : 0000000000000000
Call trace:
 drm_connector_cleanup+0x78/0x2d4 [drm]
 lt8912_bridge_detach+0x54/0x6c [lontium_lt8912b]
 drm_bridge_detach+0x44/0x84 [drm]
 drm_encoder_cleanup+0x40/0xb8 [drm]
 drmm_encoder_alloc_release+0x1c/0x30 [drm]
 drm_managed_release+0xac/0x148 [drm]
 drm_dev_put.part.0+0x88/0xb8 [drm]
 devm_drm_dev_init_release+0x14/0x24 [drm]
 devm_action_release+0x14/0x20
 release_nodes+0x5c/0x90
 devres_release_all+0x8c/0xe0
 device_unbind_cleanup+0x18/0x68
 device_release_driver_internal+0x208/0x23c
 driver_detach+0x4c/0x94
 bus_remove_driver+0x70/0xf4
 driver_unregister+0x30/0x60
 platform_driver_unregister+0x14/0x20
 tidss_platform_driver_exit+0x18/0xb2c [tidss]
 __arm64_sys_delete_module+0x1a0/0x2b4
 invoke_syscall+0x48/0x110
 el0_svc_common.constprop.0+0x60/0x10c
 do_el0_svc_compat+0x1c/0x40
 el0_svc_compat+0x40/0xac
 el0t_32_sync_handler+0xb0/0x138
 el0t_32_sync+0x194/0x198
Code: 9104a276 f2fbd5b7 aa0203e1 91008af8 (f85c0420)

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2023-52856?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2023-52856?

Apply the vendor's patch.

## Is CVE-2023-52856 being exploited?

There is no known exploitation of CVE-2023-52856 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-2023-52856 and fix it if it is affected.

What it is: CVE-2023-52856 is a medium-severity vulnerability in Linux kernel, published on 21 May 2024. 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-2023-52856 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-2023-52856/ (Markdown: https://insights.sbomify.com/CVE-2023-52856/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2023-52856
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2023-52856
- OSV: https://osv.dev/vulnerability/CVE-2023-52856

---
From sbomify Insights: https://insights.sbomify.com/CVE-2023-52856/
Summaries are generated and may contain mistakes; the official description above is the record.