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NVD / CVE Program· CNA Linux

CVE-2021-47555: net: vlan: fix underflow for the real_dev refcnt

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 01d9cc2dea3fde3bad6d27f464eff463496e2b00, 5.10.83, 5.15.
  • Severity is disputed: the assigning authority (CNA) scores it 7.8, NVD 5.5.
  • Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Low priority for now. Upgrade to Linux Linux 01d9cc2dea3fde3bad6d27f464eff463496e2b00, 5.10.83, 5.15 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: net: vlan: fix underflow for the real_dev refcnt Inject error before dev_hold(real_dev) in register_vlan_dev(), and execute the following testcase: ip link add dev dummy1 type dummy ip link add name dummy1.100 link dummy1 type vlan id 100 ip link del dev dummy1 When the dummy netdevice is removed, we will get a WARNING as following: ======================================================================= refcount_t: decrement hit 0; leaking memory. WARNING: CPU: 2 PID: 0 at lib/refcount.c:31 refcount_warn_saturate+0xbf/0x1e0 and an endless loop of: ======================================================================= unregister_netdevice: waiting for dummy1 to become free. Usage count = -1073741824 That is because dev_put(real_dev) in vlan_dev_free() be called without dev_hold(real_dev) in register_vlan_dev(). It makes the refcnt of real_dev underflow. Move the dev_hold(real_dev) to vlan_dev_init() which is the call-back of ndo_init(). That makes dev_hold() and dev_put() for vlan's real_dev symmetrical.

MediumCVSS 5.5 · v3.1—No exploit Fix available
Published
May 24, 2024
Updated
Aug 5, 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.

CNA vs NVD score

NVD
5.5
CNA · Linux
7.8
2.3 point gap

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

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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  • 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.

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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 kernel5.4.160 and later · before 5.4.163
  • linux linux kernel5.10.80 and later · before 5.10.83
  • linux linux kernel5.14.19 and later · before 5.15
  • linux linux kernel5.15.3 and later · before 5.15.6
  • linux linux kernel5.16

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

    • fca96b3f852a1b369b7b2844ce357cd689879934affected
    • 700602b662d7eaa816b1a3cb0abe7a85de358fd4 and later · before 5e44178864b38dd70b877985abd7d86fdb95f27daffected · git
    • e04a7a84bb77f9cdf4475340fe931389bc72331c and later · before 6e800ee43218a56acc93676bbb3d93b74779e555affected · git
    • 21032425c36ff85f16e72ca92193a8c401e4acd5 and later · before f7fc72a508cf115c273a7a29350069def1041890affected · git
    • 563bcbae3ba233c275c244bfce2efe12938f5363 and later · before 01d9cc2dea3fde3bad6d27f464eff463496e2b00affected · git
    • 5.14.19 and later · before 5.15affected · semver
    • 5.4.160 and later · before 5.4.163affected · semver
    • 5.10.80 and later · before 5.10.83affected · semver
    • 5.15.3 and later · before 5.15.6affected · semver

Package-level exposure

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

EcosystemPackageAffected rangeFix
Debian:12linuxbefore 5.15.15-15.15.15-1
openSUSE:Leap 15.5dtb-aarch64before 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-64kbbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-azurebefore 5.14.21-150500.33.60.15.14.21-150500.33.60.1
openSUSE:Leap 15.5kernel-debugbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-docsbefore 5.14.21-150500.55.73.25.14.21-150500.55.73.2
openSUSE:Leap 15.5kernel-kvmsmallbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-obs-buildbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-obs-qabefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-rtbefore 5.14.21-150500.13.61.15.14.21-150500.13.61.1
openSUSE:Leap 15.5kernel-rt_debugbefore 5.14.21-150500.13.61.15.14.21-150500.13.61.1
openSUSE:Leap 15.5kernel-sourcebefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-source-azurebefore 5.14.21-150500.33.60.15.14.21-150500.33.60.1
openSUSE:Leap 15.5kernel-source-rtbefore 5.14.21-150500.13.61.15.14.21-150500.13.61.1
openSUSE:Leap 15.5kernel-symsbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap 15.5kernel-syms-azurebefore 5.14.21-150500.33.60.15.14.21-150500.33.60.1
openSUSE:Leap 15.5kernel-syms-rtbefore 5.14.21-150500.13.61.15.14.21-150500.13.61.1
openSUSE:Leap 15.5kernel-zfcpdumpbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap Micro 5.5kernel-defaultbefore 5.14.21-150500.55.73.15.14.21-150500.55.73.1
openSUSE:Leap Micro 5.5kernel-default-basebefore 5.14.21-150500.55.73.1.150500.6.33.85.14.21-150500.55.73.1.150500.6.33.8
SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOSkernel-64kbbefore 5.14.21-150400.24.125.15.14.21-150400.24.125.1
SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOSkernel-docsbefore 5.14.21-150400.24.125.15.14.21-150400.24.125.1
SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOSkernel-obs-buildbefore 5.14.21-150400.24.125.15.14.21-150400.24.125.1
SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOSkernel-sourcebefore 5.14.21-150400.24.125.15.14.21-150400.24.125.1

+24

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-2021-47553May 24, 2024 · sched/scs: Reset task stack state in bringup_cpu()
    31Monitor
  • ← EarlierCVE-2021-47554May 24, 2024 · vdpa_sim: avoid putting an uninitialized iova_domain
    22Monitor
  • Later →CVE-2021-47556May 24, 2024 · ethtool: ioctl: fix potential NULL deref in ethtool_set_coalesce()
    22Monitor

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 Linux01d9cc2dea3fde3bad6d27f464eff463496e2b00Vendor (CNA)
Linux Linux5.10.83Vendor (CNA)
Linux Linux5.15Vendor (CNA)
Linux Linux5.15.6Vendor (CNA)
Linux Linux5.4.163Vendor (CNA)
Linux Linux5e44178864b38dd70b877985abd7d86fdb95f27dVendor (CNA)
Linux Linux6e800ee43218a56acc93676bbb3d93b74779e555Vendor (CNA)
Linux Linuxf7fc72a508cf115c273a7a29350069def1041890Vendor (CNA)
debian:linux5.15.15-1 · Debian:12Package registry (OSV)
opensuse:dtb-aarch645.14.21-150500.55.73.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-64kb5.14.21-150500.55.73.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-azure5.14.21-150500.33.60.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-debug5.14.21-150500.55.73.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-default5.14.21-150500.55.73.1 · openSUSE:Leap Micro 5.5Package registry (OSV)
opensuse:kernel-default-base5.14.21-150500.55.73.1.150500.6.33.8 · openSUSE:Leap Micro 5.5Package registry (OSV)
opensuse:kernel-rt5.14.21-150500.13.61.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-rt_debug5.14.21-150500.13.61.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-source-azure5.14.21-150500.33.60.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-source-rt5.14.21-150500.13.61.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-syms-azure5.14.21-150500.33.60.1 · openSUSE:Leap 15.5Package registry (OSV)
opensuse:kernel-syms-rt5.14.21-150500.13.61.1 · openSUSE:Leap 15.5Package registry (OSV)
suse:kernel-64kb5.14.21-150400.24.125.1 · SUSE:Linux Enterprise High Performance Computing 15 SP4-ESPOSPackage registry (OSV)
suse:kernel-azure5.14.21-150500.33.60.1 · SUSE:Linux Enterprise Module for Public Cloud 15 SP5Package registry (OSV)
suse:kernel-default5.14.21-150400.24.125.1 · SUSE:Linux Enterprise Micro 5.3Package registry (OSV)
suse:kernel-default-base5.14.21-150400.24.125.1.150400.24.60.1 · SUSE:Linux Enterprise Micro 5.3Package registry (OSV)
suse:kernel-livepatch-SLE15-SP4_Update_281-150400.9.3.1 · SUSE:Linux Enterprise Live Patching 15 SP4Package registry (OSV)
suse:kernel-livepatch-SLE15-SP5-RT_Update_171-150500.11.3.1 · SUSE:Linux Enterprise Live Patching 15 SP5Package registry (OSV)
suse:kernel-rt5.14.21-150400.15.85.1 · SUSE:Linux Enterprise Micro 5.3Package registry (OSV)
suse:kernel-rt5.14.21-150500.13.61.1 · SUSE:Linux Enterprise Micro 5.5Package registry (OSV)
suse:kernel-rt_debug5.14.21-150500.13.61.1 · SUSE:Real Time Module 15 SP5Package registry (OSV)

+5

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.

No history yet (it accumulates with the daily EPSS job).

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-2024-2682837 days apartcifs: fix underflow in parse_server_interfaces()
    37Monitor
  • CVE-2024-2691337 days apartdrm/amd/display: Fix dcn35 8k30 Underflow/Corruption Issue
    31Monitor
  • CVE-2024-46759117 days aparthwmon: (adc128d818) Fix underflows seen when writing limit attributes
    31Monitor
  • CVE-2024-53061179 days apartmedia: s5p-jpeg: prevent buffer overflows
    31Monitor
  • CVE-2024-0565130 days apartKernel: cifs filesystem decryption improper input validation remote code execution vulnerability in function receive_encrypted_standard of client
    30Monitor
  • CVE-2022-49278278 days apartremoteproc: Fix count check in rproc_coredump_write()
    28Monitor

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-191 · Integer Underflow (Wrap or Wraparound)

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 (3 more)

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

All records