CVE-2021-27861: Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with inval

Q: How do I fix CVE-2021-27861?

ieee 802.2: upgrade to newer than 802.2h-1997; p802.1q: upgrade to newer than d1.0. Exact commands for each OS are on this page.

Q: Is CVE-2021-27861 being exploited?

CVE-2021-27861 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-27861 affect?

CVE-2021-27861 affects ieee 802.2, p802.1q. Severity is medium (CVSS 4.7). Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with invalid length (and optionally VLAN0 headers)

Q: How urgent is CVE-2021-27861?

Priority 29/100. No elevated risk signals yet.

Routine

MEDIUM 4.7UPGRADEUPGRADE

CVE-2021-27861 is a medium-severity flaw (CVSS 4.7) affecting ieee 802.2, p802.1q. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with invalid length (and optionally VLAN0 headers)

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.7 (Medium)
Attack vector	Adjacent network
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.7% (top 48%)
CISA exploited list	No
Weakness	CWE-130, CWE-290
Published	2022-09-27
Last modified	2026-06-17

Publisher (CNA): CERT/CC · Vendor: ieee · ietf

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2022-09-27 19:15 UTCPublished CVE record published
2026-06-17 03:45 UTCUpdated Record last modified

ieee ieee 802.2 UPGRADE

Affected: <= 802.2h-1997

Fixed in: newer than 802.2h-1997

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy ieee-802.2 || rpm -q ieee-802.2 || ieee-802.2 --version

2. UPGRADE to newer than 802.2h-1997 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade ieee-802.2

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade ieee-802.2

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

ietf p802.1q UPGRADE

Affected: <= d1.0

Fixed in: newer than d1.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy p802.1q || rpm -q p802.1q || p802.1q --version

2. UPGRADE to newer than d1.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade p802.1q

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade p802.1q

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-27861?

ieee 802.2: upgrade to newer than 802.2h-1997; p802.1q: upgrade to newer than d1.0. Exact commands for each OS are on this page.

Is CVE-2021-27861 being exploited?

CVE-2021-27861 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-27861 affect?

CVE-2021-27861 affects ieee 802.2, p802.1q. Severity is medium (CVSS 4.7). Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with invalid length (and optionally VLAN0 headers)

How urgent is CVE-2021-27861?

Priority 29/100. No elevated risk signals yet.

Related CVEs

CVE-2021-27862 MEDIUM 4.7 UPGRADE UPGRADE Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using LLC/SNAP headers with inval
CVE-2021-27854 MEDIUM 4.7 UPGRADE UPGRADE Layer 2 network filtering capabilities such as IPv6 RA guard can be bypassed using combinations of VLAN 0 head
CVE-2021-27853 MEDIUM 4.7 UPGRADE UPGRADE Layer 2 network filtering capabilities such as IPv6 RA guard or ARP inspection can be bypassed using combinati

References

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