CVE-2021-4090Public exploitNetwork attack vector

Kernel memory overwrite via oversized NFSv4 bitmap

Published Feb 18, 2022 · Updated Aug 25, 2026

An NFSD out-of-bounds write in affected Linux kernels and the SIMATIC GNU/Linux subsystem allows attackers to corrupt kernel memory via NFSv4. nfsd4_decode_bitmap4 trusts the RPC bitmap word count and copies client-supplied words past the bmval array during EXCHANGE_ID decoding. A reachable NFSv4 server is required; a crafted client request can crash the server, while published assessments also identify confidentiality and integrity risk.

CVSS severity7.1
High
EPSS probability0.34%
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

An NFSD out-of-bounds write in affected Linux kernels and the SIMATIC GNU/Linux subsystem allows attackers to corrupt kernel memory via NFSv4. nfsd4_decode_bitmap4 trusts the RPC bitmap word count and copies client-supplied words past the bmval array during EXCHANGE_ID decoding. A reachable NFSv4 server is required; a crafted client request can crash the server, while published assessments also identify confidentiality and integrity risk.

The record

CVE
CVE-2021-4090
Published
Feb 18, 2022
Updated
Aug 25, 2026
Vendor
Siemens
Product
SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
Classifications
CWE-787, T1068
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Feb 18, 2022CVE publishedPublication date reported by the CVE source.
  2. Aug 25, 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=0 <*

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Siemens · SIMATIC S7-1500 TM MFP - GNU/Linux subsystemversion=0 <*
The Linux Kernel Organization · Linux Kernelversion=5.11 <5.15.5

Published CVSS scores

6.6NIST NVDAV:L/AC:L/Au:N/C:C/I:C/A:N
5.3Siemens ProductCERTCVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
7.1NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

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)
Vectornetwork
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-787Out-of-bounds Write
T1068Exploitation for Privilege Escalation

Public exploit references

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