CVE-2023-53121

Kernel crash via unsafe per-CPU counter update

Published May 2, 2025 · Updated May 11, 2026

A TCP flaw in the Linux kernel allows local users to crash the kernel through SYN-ACK retransmission from process context. tcp_rtx_synack() can invoke tcp_make_synack() with preemption enabled, where __TCP_INC_STATS() updates a per-CPU variable that requires non-preemptible context. A low-privileged local user must reach the TCP send path that retransmits a SYN-ACK; the resulting preemption check triggers a kernel BUG and interrupts the host.

CVSS severity5.5
Medium
EPSS probability0.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

A TCP flaw in the Linux kernel allows local users to crash the kernel through SYN-ACK retransmission from process context. tcp_rtx_synack() can invoke tcp_make_synack() with preemption enabled, where __TCP_INC_STATS() updates a per-CPU variable that requires non-preemptible context. A low-privileged local user must reach the TCP send path that retransmits a SYN-ACK; the resulting preemption check triggers a kernel BUG and interrupts the host.

The record

CVE
CVE-2023-53121
Published
May 2, 2025
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. May 2, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=3.7
  2. Affected versionversion=8336886f786fdacbc19b719c1f7ea91eb70706d4 <442aa78ed70188b21ccd8669738448702c0a3281
  3. Affected versionversion=8336886f786fdacbc19b719c1f7ea91eb70706d4 <7613cde8c0c1f02a7ec2e1d536c01b65b135fc1c
  4. Affected versionversion=8336886f786fdacbc19b719c1f7ea91eb70706d4 <77ad58bca0119e8cc3e0e9d91a3f22caa66e4dfa
  5. Affected versionversion=8336886f786fdacbc19b719c1f7ea91eb70706d4 <9180aa4622a720b433e842b4d3aa34d73eec577a
  6. Affected versionversion=8336886f786fdacbc19b719c1f7ea91eb70706d4 <ad07290d63ff6689f50565b02f5b6f34ec15a5ca
  7. Affected versionversion=8336886f786fdacbc19b719c1f7ea91eb70706d4 <bced3f7db95ff2e6ca29dc4d1c9751ab5e736a09
  8. Affected versionversion=8336886f786fdacbc19b719c1f7ea91eb70706d4 <d493d4fe88195a144d6a277a90062a7534ed2192
  9. Affected versionversion=8336886f786fdacbc19b719c1f7ea91eb70706d4 <e23ca307745be3df7fe9762f3e2a7e311a57852e

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=3.7; version=8336886f786fdacbc19b719c1f7ea91eb70706d4 <442aa78ed70188b21ccd8669738448702c0a3281; version=8336886f786fdacbc19b719c1f7ea91eb70706d4 <7613cde8c0c1f02a7ec2e1d536c01b65b135fc1c; version=8336886f786fdacbc19b719c1f7ea91eb70706d4 <77ad58bca0119e8cc3e0e9d91a3f22caa66e4dfa; version=8336886f786fdacbc19b719c1f7ea91eb70706d4 <9180aa4622a720b433e842b4d3aa34d73eec577a; version=8336886f786fdacbc19b719c1f7ea91eb70706d4 <ad07290d63ff6689f50565b02f5b6f34ec15a5ca; version=8336886f786fdacbc19b719c1f7ea91eb70706d4 <bced3f7db95ff2e6ca29dc4d1c9751ab5e736a09; version=8336886f786fdacbc19b719c1f7ea91eb70706d4 <d493d4fe88195a144d6a277a90062a7534ed2192; version=8336886f786fdacbc19b719c1f7ea91eb70706d4 <e23ca307745be3df7fe9762f3e2a7e311a57852e

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo