Skip to content
Fencer Vulns
high 7.8

CVE-2021-47566 json

proc/vmcore: fix clearing user buffer by properly using clear_user()

published 2024-05-24 2 y ago modified 2026-06-17 4 mo ago also EUVD-2021-34568

cvss
7.8
version 3.1, NVD
cisa kev
Not listed
not in CISA's catalog
epss
0.2%
EPSS 0.2% chance of exploitation in 30 days, percentile 13%
public exploits
0
none known

Summary

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

proc/vmcore: fix clearing user buffer by properly using clear_user()

To clear a user buffer we cannot simply use memset, we have to use clear_user(). With a virtio-mem device that registers a vmcore_cb and has some logically unplugged memory inside an added Linux memory block, I can easily trigger a BUG by copying the vmcore via "cp":

systemd[1]: Starting Kdump Vmcore Save Service... kdump[420]: Kdump is using the default log level(3). kdump[453]: saving to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/ kdump[458]: saving vmcore-dmesg.txt to /sysroot/var/crash/127.0.0.1-2021-11-11-14:59:22/ kdump[465]: saving vmcore-dmesg.txt complete kdump[467]: saving vmcore BUG: unable to handle page fault for address: 00007f2374e01000 #PF: supervisor write access in kernel mode #PF: error_code(0x0003) - permissions violation PGD 7a523067 P4D 7a523067 PUD 7a528067 PMD 7a525067 PTE 800000007048f867 Oops: 0003 [#1] PREEMPT SMP NOPTI CPU: 0 PID: 468 Comm: cp Not tainted 5.15.0+ #6 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.14.0-27-g64f37cc530f1-prebuilt.qemu.org 04/01/2014 RIP: 0010:read_from_oldmem.part.0.cold+0x1d/0x86 Code: ff ff ff e8 05 ff fe ff e9 b9 e9 7f ff 48 89 de 48 c7 c7 38 3b 60 82 e8 f1 fe fe ff 83 fd 08 72 3c 49 8d 7d 08 4c 89 e9 89 e8 <49> c7 45 00 00 00 00 00 49 c7 44 05 f8 00 00 00 00 48 83 e7 f81 RSP: 0018:ffffc9000073be08 EFLAGS: 00010212 RAX: 0000000000001000 RBX: 00000000002fd000 RCX: 00007f2374e01000 RDX: 0000000000000001 RSI: 00000000ffffdfff RDI: 00007f2374e01008 RBP: 0000000000001000 R08: 0000000000000000 R09: ffffc9000073bc50 R10: ffffc9000073bc48 R11: ffffffff829461a8 R12: 000000000000f000 R13: 00007f2374e01000 R14: 0000000000000000 R15: ffff88807bd421e8 FS: 00007f2374e12140(0000) GS:ffff88807f000000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f2374e01000 CR3: 000000007a4aa000 CR4: 0000000000350eb0 Call Trace: read_vmcore+0x236/0x2c0 proc_reg_read+0x55/0xa0 vfs_read+0x95/0x190 ksys_read+0x4f/0xc0 do_syscall_64+0x3b/0x90 entry_SYSCALL_64_after_hwframe+0x44/0xae

Some x86-64 CPUs have a CPU feature called "Supervisor Mode Access Prevention (SMAP)", which is used to detect wrong access from the kernel to user buffers like this: SMAP triggers a permissions violation on wrong access. In the x86-64 variant of clear_user(), SMAP is properly handled via clac()+stac().

To fix, properly use clear_user() when we're dealing with a user buffer.

Patch / fix

  • Linux Linux 4.4.294, 4.9.292, 4.14.257, 4.19.219, 5.4.163, 5.10.83, 5.15.6, 5.16
  • linux Debian 14, Debian 13, Debian 12 5.15.15-1

debian advisories DEBIAN-CVE-2021-47566

  • linux Ubuntu 18.04 LTS 4.15.0-169.177
  • linux Ubuntu 20.04 LTS 5.4.0-100.113
  • linux-aws Ubuntu 18.04 LTS 4.15.0-1121.129
  • linux-aws Ubuntu 20.04 LTS 5.4.0-1066.69
  • linux-gcp Ubuntu 20.04 LTS 5.4.0-1065.69
  • linux-ibm Ubuntu 20.04 LTS 5.4.0-1015.16
  • linux-kvm Ubuntu 18.04 LTS 4.15.0-1107.109
  • linux-kvm Ubuntu 20.04 LTS 5.4.0-1056.58

ubuntu advisories UBUNTU-CVE-2021-47566

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 RHEL 8.8 EUS 4.18.0-477.74.1.el8_8
  • perf RHEL 8.8 EUS 4.18.0-477.74.1.el8_8
  • bpftool RHEL 8.8 EUS 4.18.0-477.74.1.el8_8
  • kernel-core RHEL 8.8 EUS 4.18.0-477.74.1.el8_8
  • kernel-tools RHEL 8.8 EUS 4.18.0-477.74.1.el8_8
  • python3-perf RHEL 8.8 EUS 4.18.0-477.74.1.el8_8
  • kernel-modules RHEL 8.8 EUS 4.18.0-477.74.1.el8_8
  • kernel-zfcpdump RHEL 8.8 EUS 4.18.0-477.74.1.el8_8

red hat advisories RHSA-2024:6993RHSA-2024:5281

  • dtb-aarch64 openSUSE Leap 15.5 5.14.21-150500.55.73.1
  • kernel-64kb SLE Module for Basesystem 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.73.1
  • kernel-syms SLE Module for Development Tools 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.73.1
  • kernel-obs-qa openSUSE Leap 15.5 5.14.21-150500.55.73.1
  • kernel-source SLE Module for Development Tools 15 SP5, SLE Module for Basesystem 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.73.1
  • kernel-default SLE Workstation Extension 15 SP5, SLE Module for Legacy 15 SP5, SLE Module for Basesystem 15 SP5 +5 more 5.14.21-150500.55.73.1
  • kernel-kvmsmall openSUSE Leap 15.5 5.14.21-150500.55.73.1
  • kernel-zfcpdump SLE Module for Basesystem 15 SP5, openSUSE Leap 15.5 5.14.21-150500.55.73.1

suse advisories SUSE-SU-2024:2939-1SUSE-SU-2024:2561-1SUSE-SU-2024:2394-1SUSE-SU-2024:2381-1SUSE-SU-2024:2372-1SUSE-SU-2024:2360-1

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-2021-47566 updated cvss 5.5

kernel: proc/vmcore: fix clearing user buffer by properly using clear_user()

  • 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 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more
    affected: no fix available
  • Red Hat CodeReady Linux Builder EUS (v.8.8) kernel-debuginfo-common-x86_64 4.18.0-477.74.1.el8_8, kernel-debuginfo-common-aarch64 4.18.0-477.74.1.el8_8, kernel-debuginfo-common-ppc64le 4.18.0-477.74.1.el8_8
    fixed: vendor fix RHSA-2024:6993
  • Red Hat Enterprise Linux BaseOS AUS (v.8.6) perf 4.18.0-372.118.1.el8_6, kernel 4.18.0-372.118.1.el8_6, bpftool 4.18.0-372.118.1.el8_6, kernel-core 4.18.0-372.118.1.el8_6, kernel-tools 4.18.0-372.118.1.el8_6, python3-perf 4.18.0-372.118.1.el8_6, +8 more Red Hat Enterprise Linux BaseOS E4S (v.8.6) perf 4.18.0-372.118.1.el8_6, kernel 4.18.0-372.118.1.el8_6, bpftool 4.18.0-372.118.1.el8_6, kernel-core 4.18.0-372.118.1.el8_6, kernel-tools 4.18.0-372.118.1.el8_6, python3-perf 4.18.0-372.118.1.el8_6, +15 more
    fixed: vendor fix RHSA-2024:5281
  • Red Hat Enterprise Linux BaseOS EUS (v.8.8) perf 4.18.0-477.74.1.el8_8, kernel 4.18.0-477.74.1.el8_8, bpftool 4.18.0-477.74.1.el8_8, kernel-core 4.18.0-477.74.1.el8_8, kernel-tools 4.18.0-477.74.1.el8_8, python3-perf 4.18.0-477.74.1.el8_8, +15 more
    fixed: vendor fix RHSA-2024:6993
  • Red Hat Enterprise Linux BaseOS TUS (v.8.6) perf 4.18.0-372.118.1.el8_6, kernel 4.18.0-372.118.1.el8_6, bpftool 4.18.0-372.118.1.el8_6, kernel-core 4.18.0-372.118.1.el8_6, kernel-tools 4.18.0-372.118.1.el8_6, python3-perf 4.18.0-372.118.1.el8_6, +8 more
    fixed: vendor fix RHSA-2024:5281
  • Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +83 more Red Hat Enterprise Linux BaseOS AUS (v.8.6) kernel-headers 4.18.0-372.118.1.el8_6, kernel-cross-headers 4.18.0-372.118.1.el8_6 Red Hat Enterprise Linux BaseOS E4S (v.8.6) kernel-headers 4.18.0-372.118.1.el8_6, kernel-cross-headers 4.18.0-372.118.1.el8_6 Red Hat Enterprise Linux BaseOS TUS (v.8.6) kernel-headers 4.18.0-372.118.1.el8_6, kernel-cross-headers 4.18.0-372.118.1.el8_6
    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 SSVC

Exploitation
none
Automatable
no
Technical impact
partial
Assessed
2 y ago

Exploit prediction

0.23% chance of exploitation in the next 30 days, higher than 13% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
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

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.