CVE-2025-21820

System hang via SysRq lock-order inversion

Published Feb 27, 2025 · Updated May 11, 2026

Improper locking in the Linux kernel Xilinx UARTPS driver allows local users to hang the system through serial-console SysRq handling. cdns_uart_console_write can acquire the UART port lock while holding the console lock as the interrupt path holds the port lock and enters printk, creating a circular wait. Reachability requires local low-privilege access and an affected kernel using the Xilinx UARTPS console; successful triggering can deadlock the kernel and halt service.

CVSS severity5.5
Medium
EPSS probability0.16%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Improper locking in the Linux kernel Xilinx UARTPS driver allows local users to hang the system through serial-console SysRq handling. cdns_uart_console_write can acquire the UART port lock while holding the console lock as the interrupt path holds the port lock and enters printk, creating a circular wait. Reachability requires local low-privilege access and an affected kernel using the Xilinx UARTPS console; successful triggering can deadlock the kernel and halt service.

The record

CVE
CVE-2025-21820
Published
Feb 27, 2025
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-667, T1499.004
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 27, 2025CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=4.6
  2. Affected versionversion=74ea66d4ca061a3cd4c0e924e51b60e924644852 <4410dba9807a17a93f649a9f5870ceaf30a675a3
  3. Affected versionversion=74ea66d4ca061a3cd4c0e924e51b60e924644852 <8ea0e7b3d7b8f2f0fc9db491ff22a0abe120801c
  4. Affected versionversion=74ea66d4ca061a3cd4c0e924e51b60e924644852 <9b88a7c4584ba67267a051069b8abe44fc9595b2
  5. Affected versionversion=74ea66d4ca061a3cd4c0e924e51b60e924644852 <b06f388994500297bb91be60ffaf6825ecfd2afe
  6. Affected versionversion=74ea66d4ca061a3cd4c0e924e51b60e924644852 <de5bd24197bd9ee37ec1e379a3d882bbd15c5065
  7. Affected versionversion=74ea66d4ca061a3cd4c0e924e51b60e924644852 <e22a97700901ba5e8bf8db68056a0d50f9440cae

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.6; version=74ea66d4ca061a3cd4c0e924e51b60e924644852 <4410dba9807a17a93f649a9f5870ceaf30a675a3; version=74ea66d4ca061a3cd4c0e924e51b60e924644852 <8ea0e7b3d7b8f2f0fc9db491ff22a0abe120801c; version=74ea66d4ca061a3cd4c0e924e51b60e924644852 <9b88a7c4584ba67267a051069b8abe44fc9595b2; version=74ea66d4ca061a3cd4c0e924e51b60e924644852 <b06f388994500297bb91be60ffaf6825ecfd2afe; version=74ea66d4ca061a3cd4c0e924e51b60e924644852 <de5bd24197bd9ee37ec1e379a3d882bbd15c5065; version=74ea66d4ca061a3cd4c0e924e51b60e924644852 <e22a97700901ba5e8bf8db68056a0d50f9440cae

Published CVSS scores

5.5NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-667Improper Locking
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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