CVE-2021-27862Public exploit

Filter bypass via invalid-length LLC/SNAP conversion

Published Sep 27, 2022 · Updated Nov 4, 2025

Authentication bypass in IEEE 802.2 802.2h-1997 and IETF IPv6 RA Guard 08 allows attackers to pass rogue RAs through L2 filters. During Ethernet-to-Wi-Fi conversion, Linux mac80211 ignores an invalid 802.3 length and converts the LLC/SNAP payload into a valid 802.11 frame. An attacker on the same Layer 2 path must reach a device that converts the crafted frame and enforces RA Guard; a successful bypass can redirect or blackhole victim traffic.

CVSS severity4.7
Medium
EPSS probability0.66%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in IEEE 802.2 802.2h-1997 and IETF IPv6 RA Guard 08 allows attackers to pass rogue RAs through L2 filters. During Ethernet-to-Wi-Fi conversion, Linux mac80211 ignores an invalid 802.3 length and converts the LLC/SNAP payload into a valid 802.11 frame. An attacker on the same Layer 2 path must reach a device that converts the crafted frame and enforces RA Guard; a successful bypass can redirect or blackhole victim traffic.

The record

CVE
CVE-2021-27862
Published
Sep 27, 2022
Updated
Nov 4, 2025
Vendor
IEEE
Product
IEEE 802.2
Classifications
CWE-290, CWE-130, T1557
Attack vector
adjacent
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 27, 2022CVE publishedPublication date reported by the CVE source.
  2. Nov 4, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=802.2h-1997 <=802.2h-1997

What conditions does exploitation require?

Attack vectoradjacent
Required privilegesunauthenticated

What is affected?

IEEE · IEEE 802.2version=802.2h-1997 <=802.2h-1997
Internet Engineering Task Force (IETF) · IPv6 Router Advertisement Guardversion=08 <=08

Published CVSS scores

4.7NIST NVDCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
4.7CISA-ADPCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectoradjacent
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-290Authentication Bypass by Spoofing
CWE-130Improper Handling of Length Parameter Inconsistency
T1557Adversary-in-the-Middle

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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