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Fencer Vulns
high 7.1

CVE-2021-4090 json

An out-of-bounds (OOB) memory write flaw was found in the NFSD in the Linux kernel.

published 2022-02-18 4 y ago modified 2026-10-14 26 d ago also EUVD-2021-33977

cvss
7.1
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.3%
EPSS 0.3% chance of exploitation in 30 days, percentile 27%
public exploits
0
none known

Summary

An out-of-bounds (OOB) memory write flaw was found in the NFSD in the Linux kernel. Missing sanity may lead to a write beyond bmval[bmlen-1] in nfsd4_decode_bitmap4 in fs/nfsd/nfs4xdr.c. In this flaw, a local attacker with user privilege may gain access to out-of-bounds memory, leading to a system integrity and confidentiality threat.

Patch / fix

  • Linux kernel 5.15.5
  • Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem V1.1.1
  • linux Debian 14, Debian 13, Debian 12 5.15.5-1

debian advisories DEBIAN-CVE-2021-4090

  • linux-aws-5.11 Ubuntu 20.04 LTS 5.11.0-1028.31~20.04.1
  • linux-aws-5.13 Ubuntu 20.04 LTS 5.13.0-1012.13~20.04.1
  • linux-gcp-5.11 Ubuntu 20.04 LTS 5.11.0-1029.33~20.04.3
  • linux-gcp-5.13 Ubuntu 20.04 LTS 5.13.0-1013.16~20.04.1
  • linux-hwe-5.13 Ubuntu 20.04 LTS 5.13.0-28.31~20.04.1
  • linux-oem-5.13 Ubuntu 20.04 LTS 5.13.0-1029.36
  • linux-oem-5.14 Ubuntu 20.04 LTS 5.14.0-1018.19
  • linux-azure-5.11 Ubuntu 20.04 LTS 5.11.0-1028.31~20.04.2

ubuntu advisories UBUNTU-CVE-2021-4090

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • kernel CBL-Mariner 2.0 5.15.26.1-1

azure linux advisories AZL-8654

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2021-4090 updated cvss 7.1

kernel: Overflow of bmval[bmlen-1] in nfsd4_decode_bitmap function

  • Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +82 more
    not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-24-102-01 updated cvss 5.3

Siemens SIMATIC S7-1500 TM MFP

  • Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
    affected: mitigation, no fix available

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

0.34% chance of exploitation in the next 30 days, higher than 27% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
NVD 3.1 7.1 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
NVD 2.0 6.6 AV:L/AC:L/Au:N/C:C/I:C/A:N

Affected products

  • Linux kernel
  • Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem

Classification

Weakness
Technology feeds

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.