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Fencer Vulns
critical 9.8

CVE-2021-47107 in the critical feed json

NFSD: Fix READDIR buffer overflow

published 2024-03-04 2 y ago modified 2026-10-14 26 d ago also EUVD-2021-33755

cvss
9.8
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.8%
EPSS 0.8% chance of exploitation in 30 days, percentile 58%
public exploits
0
none known

Summary

In the Linux kernel, the following vulnerability has been resolved:

NFSD: Fix READDIR buffer overflow

If a client sends a READDIR count argument that is too small (say, zero), then the buffer size calculation in the new init_dirlist helper functions results in an underflow, allowing the XDR stream functions to write beyond the actual buffer.

This calculation has always been suspect. NFSD has never sanity- checked the READDIR count argument, but the old entry encoders managed the problem correctly.

With the commits below, entry encoding changed, exposing the underflow to the pointer arithmetic in xdr_reserve_space().

Modern NFS clients attempt to retrieve as much data as possible for each READDIR request. Also, we have no unit tests that exercise the behavior of READDIR at the lower bound of @count values. Thus this case was missed during testing.

Patch / fix

  • Linux Linux 5.15.12, 5.16
  • Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem V1.1.1
  • linux Debian 14, Debian 13, Debian 12 5.15.15-1

debian advisories DEBIAN-CVE-2021-47107

  • kernel RHEL 8 4.18.0-425.3.1.el8
  • perf RHEL 8 4.18.0-425.3.1.el8
  • bpftool RHEL 8 4.18.0-425.3.1.el8
  • kernel-core RHEL 8 4.18.0-425.3.1.el8
  • kernel-tools RHEL 8 4.18.0-425.3.1.el8
  • python3-perf RHEL 8 4.18.0-425.3.1.el8
  • kernel-modules RHEL 8 4.18.0-425.3.1.el8
  • kernel-zfcpdump RHEL 8 4.18.0-425.3.1.el8

red hat advisories RHSA-2022:7683

  • kernel-azure SLE Module for Public Cloud 15 SP5, openSUSE Leap 15.5 5.14.21-150500.33.48.1
  • kernel-syms-azure SLE Module for Public Cloud 15 SP5, openSUSE Leap 15.5 5.14.21-150500.33.48.1
  • kernel-source-azure SLE Module for Public Cloud 15 SP5, openSUSE Leap 15.5 5.14.21-150500.33.48.1
  • dtb-aarch64 openSUSE Leap 15.5 5.14.21-150500.55.59.1
  • kernel-64kb SLE Module for Basesystem 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.59.1
  • kernel-syms SLE Module for Development Tools 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.59.1
  • kernel-obs-qa openSUSE Leap 15.5 5.14.21-150500.55.59.1
  • kernel-source SLE Module for Development Tools 15 SP5, SLE Module for Basesystem 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.59.1

suse advisories SUSE-SU-2024:1490-1SUSE-SU-2024:1480-1SUSE-SU-2024:1466-1SUSE-SU-2024:1321-1SUSE-SU-2024:1320-1

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-2021-47107 updated cvss 7.1

kernel: NFSD: Fix READDIR buffer overflow

  • 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
    affected: no fix planned “Out of support scope”
  • Red Hat Enterprise Linux 8 kernel-rt, kernel-rt-kvm, kernel-rt-core, kernel-rt-modules, kernel-rt-debug-kvm, kernel-rt-debug-core, +6 more
    affected: no fix available
  • Red Hat CodeReady Linux Builder (v. 8) kernel-debuginfo-common-x86_64 4.18.0-425.3.1.el8, kernel-debuginfo-common-aarch64 4.18.0-425.3.1.el8, kernel-debuginfo-common-ppc64le 4.18.0-425.3.1.el8 Red Hat Enterprise Linux BaseOS (v. 8) perf 4.18.0-425.3.1.el8, kernel 4.18.0-425.3.1.el8, bpftool 4.18.0-425.3.1.el8, kernel-core 4.18.0-425.3.1.el8, kernel-tools 4.18.0-425.3.1.el8, python3-perf 4.18.0-425.3.1.el8, +15 more
    fixed: vendor fix RHSA-2022:7683
  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 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 6.3

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

CISA SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

0.85% chance of exploitation in the next 30 days, higher than 58% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

  • git.kernel.org https://git.kernel.org/stable/c/9e291a6a28d32545ed2fd959a8165144d1724df1 referenced PoC, tagged "exploit" by a source, unverified
  • git.kernel.org https://git.kernel.org/stable/c/eabc0aab98e5218ceecd82069b0d6fdfff5ee885 referenced PoC, tagged "exploit" by a source, unverified
  • git.kernel.org https://git.kernel.org/stable/c/53b1119a6e5028b125f431a0116ba73510d82a72 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by version score vector
CNA 3.1 9.8 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD 3.1 7.8 CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

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

Classification

Weakness
  • CWE-120 Buffer Copy without Checking Size of Input
Technology feeds

References

Sources

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