CVE-2021-47555

Medium

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.

Package Linux Kernel
Published 2024-05-24
Last modified 2025-09-18
CVSS version 3.1
Patch available
Yes

CVSS 3.1 score

5.5

out of 10
Medium
Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
High
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness type

CWE-191

CVE-2021-47555 is classified as CWE-191

See CWE-191 on MITRE CWE for full details on this weakness type.

Affected versions

Linux kernel versions 5.14.19, 5.4.160, 5.10.80, 5.15.3 and later are affected. Fixed in 5.15, 5.4.163, 5.10.83, 5.15.6 and their respective stable series.

Affected from
≥ 5.14.19 ≥ 5.4.160 ≥ 5.10.80 ≥ 5.15.3
Fixed in
✓ 5.15 5.15.x ✓ 5.4.163 5.4.x ✓ 5.10.83 5.10.x ✓ 5.15.6 5.15.x

References

4 total

Frequently asked questions

  • What is CVE-2021-47555?

    CVE-2021-47555 is a Medium severity Linux kernel vulnerability with a CVSS score of 5.5 out of 10 . It affects Linux kernel versions from 5.14.19 onward and has been patched in 5.15, 5.4.163, 5.10.83 and others. CVE-2021-47555 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

  • What is the CVSS score for CVE-2021-47555?

    CVE-2021-47555 has a CVSS score of 5.5 out of 10, rated Medium severity (CVSS 3.1). The vector string is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H .

  • Is there a patch available for CVE-2021-47555?

    Yes. CVE-2021-47555 has been patched. Fixed versions include 5.15, 5.4.163, 5.10.83 and others. If you are running Linux kernel 5.14.19 or later up to the fix versions, apply the relevant patch for your kernel branch.

  • Is CVE-2021-47555 actively exploited?

    No. CVE-2021-47555 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

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