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NVD / CVE Program· CNA Linux

CVE-2021-47221: mm/slub: actually fix freelist pointer vs redzoning

Noroxi assessment

Priority: Monitor (action score 22/100)

  • The sources we track (CISA KEV, Exploit-DB, Metasploit, Nuclei, GitHub) show no public exploit code or exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.22% (FIRST EPSS).
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux ce6e8bee7a3883e8008b30f5887dbb426aac6a35, e41a49fadbc80b60b48d3c095d9e2ee7ef7c9a8e, f6ed2357541612a13a5841b3af4dc32ed984a25f.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux ce6e8bee7a3883e8008b30f5887dbb426aac6a35, e41a49fadbc80b60b48d3c095d9e2ee7ef7c9a8e, f6ed2357541612a13a5841b3af4dc32ed984a25f or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

In the Linux kernel, the following vulnerability has been resolved: mm/slub: actually fix freelist pointer vs redzoning It turns out that SLUB redzoning ("slub_debug=Z") checks from s->object_size rather than from s->inuse (which is normally bumped to make room for the freelist pointer), so a cache created with an object size less than 24 would have the freelist pointer written beyond s->object_size, causing the redzone to be corrupted by the freelist pointer. This was very visible with "slub_debug=ZF": BUG test (Tainted: G B ): Right Redzone overwritten ----------------------------------------------------------------------------- INFO: 0xffff957ead1c05de-0xffff957ead1c05df @offset=1502. First byte 0x1a instead of 0xbb INFO: Slab 0xffffef3950b47000 objects=170 used=170 fp=0x0000000000000000 flags=0x8000000000000200 INFO: Object 0xffff957ead1c05d8 @offset=1496 fp=0xffff957ead1c0620 Redzone (____ptrval____): bb bb bb bb bb bb bb bb ........ Object (____ptrval____): 00 00 00 00 00 f6 f4 a5 ........ Redzone (____ptrval____): 40 1d e8 1a aa @.... Padding (____ptrval____): 00 00 00 00 00 00 00 00 ........ Adjust the offset to stay within s->object_size. (Note that no caches of in this size range are known to exist in the kernel currently.)

MediumCVSS 5.5 · v3.1—No exploit Fix available
Published
May 21, 2024
Updated
Jun 17, 2026
EPSS
0.2% · 12th percentile

Report tools

JSON

Action score

22

Monitor

Low priority for now.

CVSS
22 / 40 · 5.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.2%

CISA SSVC decision

Exploitation
none
Automatable
no
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • No public exploit code on record
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2021-47221

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel5.7 and later · before 5.10.46
  • linux linux kernel5.11 and later · before 5.12.13
  • linux linux kernel5.13

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 5.7affected
    • 89b83f282d8ba380cf2124f88106c57df49c538c and later · before f6ed2357541612a13a5841b3af4dc32ed984a25faffected · git
    • 89b83f282d8ba380cf2124f88106c57df49c538c and later · before ce6e8bee7a3883e8008b30f5887dbb426aac6a35affected · git
    • 89b83f282d8ba380cf2124f88106c57df49c538c and later · before e41a49fadbc80b60b48d3c095d9e2ee7ef7c9a8eaffected · git
    • before 5.7not affected · semver
    • 5.10.46 and later · up to and including 5.10.*not affected · semver
    • 5.12.13 and later · up to and including 5.12.*not affected · semver
    • 5.13 and laternot affected · original_commit_for_fix

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 5.10.46-15.10.46-1
Red Hat:enterprise_linux:8::baseosbpftoolbefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseosbpftool-debuginfobefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernelbefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-abi-stablelistsbefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-corebefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-debugbefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-debug-corebefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-debug-debuginfobefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-debug-develbefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-debug-modulesbefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-debug-modules-extrabefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-debuginfobefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-debuginfo-common-aarch64before 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-debuginfo-common-ppc64lebefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-debuginfo-common-s390xbefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-debuginfo-common-x86_64before 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-develbefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-docbefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-modulesbefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-modules-extrabefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-toolsbefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-tools-debuginfobefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8
Red Hat:enterprise_linux:8::baseoskernel-tools-libsbefore 0:4.18.0-477.10.1.el8_80:4.18.0-477.10.1.el8_8

+11

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2024-36008May 20, 2024 · ipv4: check for NULL idev in ip_route_use_hint()
    22Monitor
  • ← EarlierCVE-2020-36788May 21, 2024 · drm/nouveau: avoid a use-after-free when BO init fails
    31Monitor
  • Later →CVE-2021-47222May 21, 2024 · net: bridge: fix vlan tunnel dst refcnt when egressing
    31Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linuxce6e8bee7a3883e8008b30f5887dbb426aac6a35Vendor (CNA)
Linux Linuxe41a49fadbc80b60b48d3c095d9e2ee7ef7c9a8eVendor (CNA)
Linux Linuxf6ed2357541612a13a5841b3af4dc32ed984a25fVendor (CNA)
debian:linux5.10.46-1 · Debian:12Package registry (OSV)
red hat:bpftool0:4.18.0-477.10.1.el8_8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:bpftool-debuginfo0:4.18.0-477.10.1.el8_8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kernel0:4.18.0-477.10.1.el8_8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kernel-abi-stablelists0:4.18.0-477.10.1.el8_8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kernel-core0:4.18.0-477.10.1.el8_8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kernel-debug0:4.18.0-477.10.1.el8_8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kernel-debug-core0:4.18.0-477.10.1.el8_8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kernel-debug-debuginfo0:4.18.0-477.10.1.el8_8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kernel-debug-devel0:4.18.0-477.10.1.el8_8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kernel-debug-modules0:4.18.0-477.10.1.el8_8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kernel-debug-modules-extra0:4.18.0-477.10.1.el8_8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)
red hat:kernel-debuginfo0:4.18.0-477.10.1.el8_8 · Red Hat:enterprise_linux:8::baseosPackage registry (OSV)

Exploit status

No known public exploit

No public exploit has been observed yet. That doesn't mean you're safe, only that the bar is a little higher.

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

No dated events beyond publication.

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2021-4708778 days aparttee: optee: Fix incorrect page free bug
    31Monitor
  • CVE-2022-48425430 days apartIn the Linux kernel through 6.2.7, fs/ntfs3/inode.c has an invalid kfree because it does not validate MFT flags before replaying logs.
    31Monitor
  • CVE-2022-4696496 days apartThere exists a use-after-free vulnerability in the Linux kernel through io_uring and the IORING_OP_SPLICE operation.
    31Monitor
  • CVE-2024-4213270 days apartbluetooth/hci: disallow setting handle bigger than HCI_CONN_HANDLE_MAX
    28Monitor
  • CVE-2021-473870 days apartcpufreq: schedutil: Use kobject release() method to free sugov_tunables
    22Monitor
  • CVE-2024-358324 days apartbcachefs: kvfree bch_fs::snapshots in bch2_fs_snapshots_exit
    22Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

All national notices →

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
none
Integrity
none
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
None
Integrity impact
None
Availability impact
High

Weakness class (CWE)

CWE-763 · Release of Invalid Pointer or Reference

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (2 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records