CVE-2021-27853: Layer 2 network filtering capabilities such as IPv6 RA guard or ARP inspection can be bypassed using combinati
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Routine
MEDIUM 4.7UPGRADEUPGRADEMITIGATE
CVE-2021-27853 is a medium-severity flaw (CVSS 4.7) affecting ieee 802.2, p802.1q, catalyst 6503-e firmware. 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 or ARP inspection can be bypassed using combinations of VLAN 0 headers and LLC/SNAP headers.
Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.
cisco catalyst 6503-e firmware MITIGATE
Affected: 15.5\(01.01.85\)sy07
Fixed in: no fixed release known
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
cisco catalyst 6504-e firmware MITIGATE
Affected: 15.5\(01.01.85\)sy07
Fixed in: no fixed release known
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
cisco catalyst 6506-e firmware MITIGATE
Affected: 15.5\(01.01.85\)sy07
Fixed in: no fixed release known
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
cisco catalyst 6509-e firmware MITIGATE
Affected: 15.5\(01.01.85\)sy07
Fixed in: no fixed release known
Safe to downgrade to: no unaffected older release
Check your OS release
cat /etc/os-release; uname -r
Debian / Ubuntu
sudo apt update && sudo apt full-upgrade
RHEL / Amazon Linux / Fedora
sudo dnf upgrade --refresh
Windows
Install the latest cumulative update from Windows Update
If no patch exists yet
OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.
Verify at the official sourceNVD · 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-2021-27853?
ieee 802.2: upgrade to newer than 802.2h-1997; p802.1q: upgrade to newer than d1.0; catalyst 6503-e firmware: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.
Is CVE-2021-27853 being exploited?
CVE-2021-27853 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-2021-27853 affect?
CVE-2021-27853 affects ieee 802.2, p802.1q, catalyst 6503-e firmware. Severity is medium (CVSS 4.7). Layer 2 network filtering capabilities such as IPv6 RA guard or ARP inspection can be bypassed using combinations of VLAN 0 headers and LLC/SNAP headers.
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