CVE-2021-27853
L2 network filtering can be bypassed using stacked VLAN0 and LLC/SNAP headers
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.
Attack profile
How easy it is to exploit
- Attack vector
- Adjacent network
- Complexity
- Low
- Privileges needed
- None
- User interaction
- None
What an attacker can affect
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
Exploit likelihood
What each source reports
NVD Score used
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.
- Record
CVE-2021-27853- CVSS 3.1
- 4.7 Medium
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N - Weakness
- CWE-290
- Updated
- 2026-11-02
CVE List
L2 network filtering can be bypassed using stacked VLAN0 and LLC/SNAP headers
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.
- Record
CVE-2021-27853- CVSS 3.1
- 4.7 Medium
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N - Weakness
- CWE-290
- Updated
- 2026-11-02
EUVDEUVD-2021-14591
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.
- Record
EUVD-2021-14591- CVSS 3.1
- 4.7 Medium
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N - Updated
- 2026-11-02
GitHub AdvisoriesGHSA-v8jg-p3fp-g968
Layer 2 network filtering capabilities such as IPv6 RA guard or ARP inspection can be bypassed...
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.
- Record
GHSA-v8jg-p3fp-g968- CVSS 3.1
- 4.7 Medium
CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N - Weakness
- CWE-290
- Updated
- 2026-11-02
Affected products
- cisco catalyst 6503-e firmware
- cisco catalyst 6504-e firmware
- cisco catalyst 6506-e firmware
- cisco catalyst 6509-e firmware
- cisco catalyst 6509-neb-a firmware
- cisco catalyst 6509-v-e firmware
- cisco catalyst 6513-e firmware
- cisco catalyst 6800ia firmware
- cisco catalyst 6807-xl firmware
- cisco catalyst 6840-x firmware
- cisco catalyst 6880-x firmware
- cisco catalyst c6816-x-le firmware
Show 85 moreShow less
- cisco catalyst c6824-x-le-40g firmware
- cisco catalyst c6832-x-le firmware
- cisco catalyst c6840-x-le-40g firmware
- cisco ios xe
- cisco meraki ms210 firmware
- cisco meraki ms225 firmware
- cisco meraki ms250 firmware
- cisco meraki ms350 firmware
- cisco meraki ms355 firmware
- cisco meraki ms390 firmware
- cisco meraki ms410 firmware
- cisco meraki ms420 firmware
- cisco meraki ms425 firmware
- cisco meraki ms450 firmware
- cisco n9k-c9316d-gx firmware
- cisco n9k-c9332d-gx2b firmware
- cisco n9k-c9348d-gx2a firmware
- cisco n9k-c93600cd-gx firmware
- cisco n9k-c9364d-gx2a firmware
- cisco n9k-x9432c-s firmware
- cisco n9k-x9464px firmware
- cisco n9k-x9464tx2 firmware
- cisco n9k-x9564px firmware
- cisco n9k-x9564tx firmware
- cisco n9k-x9636c-r firmware
- cisco n9k-x9636c-rx firmware
- cisco n9k-x97160yc-ex firmware
- cisco n9k-x9732c-ex firmware
- cisco n9k-x9732c-fx firmware
- cisco n9k-x9736c-ex firmware
- cisco n9k-x9736c-fx firmware
- cisco n9k-x9788tc-fx firmware
- cisco nexus 92160yc-x firmware
- cisco nexus 92300yc firmware
- cisco nexus 92304qc firmware
- cisco nexus 92348gc-x firmware
- cisco nexus 9236c firmware
- cisco nexus 9272q firmware
- cisco nexus 93108tc-ex firmware
- cisco nexus 93108tc-fx3p firmware
- cisco nexus 93108tc-fx firmware
- cisco nexus 93120tx firmware
- cisco nexus 93180yc-ex firmware
- cisco nexus 93180yc-fx3 firmware
- cisco nexus 93180yc-fx firmware
- cisco nexus 93216tc-fx2 firmware
- cisco nexus 93240yc-fx2 firmware
- cisco nexus 9332c firmware
- cisco nexus 93360yc-fx2 firmware
- cisco nexus 9336c-fx2-e firmware
- cisco nexus 9336c-fx2 firmware
- cisco nexus 9348gc-fxp firmware
- cisco nexus 9364c-gx firmware
- cisco nexus 9364c firmware
- cisco nexus 9432pq firmware
- cisco nexus 9504 firmware
- cisco nexus 9508 firmware
- cisco nexus 9516 firmware
- cisco nexus 9536pq firmware
- cisco nexus 9636pq firmware
- cisco nexus 9716d-gx firmware
- cisco nexus 9736pq firmware
- cisco nexus 9800 firmware
- cisco nexus x9636q-r firmware
- cisco sf-500-24mp firmware
- cisco sf500-18p firmware
- cisco sf500-24 firmware
- cisco sf500-24p firmware
- cisco sf500-48 firmware
- cisco sf500-48mp firmware
- cisco sg500-28 firmware
- cisco sg500-28mpp firmware
- cisco sg500-28p firmware
- cisco sg500-52 firmware
- cisco sg500-52mp firmware
- cisco sg500-52p firmware
- cisco sg500x-24 firmware
- cisco sg500x-24mpp firmware
- cisco sg500x-24p firmware
- cisco sg500x-48 firmware
- cisco sg500x-48mpp firmware
- cisco sg500x-48p firmware
- ieee 802.2
- ietf draft-ietf-v6ops-ra-guard
- ietf p802.1q
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | CVE List, EUVD, GitHub Advisories, NVD |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2021-27853 is a medium vulnerability (CVSS 4.7) in Cisco Catalyst 6503-e Firmware, published September 27, 2022. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 0.81%, the 57th percentile. No source names a fixed version.
References
datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08
standards.ieee.org/ieee/802.2/1048
tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-VU855201-J3z8CKTX
kb.cert.org/vuls/id/855201
blog.champtar.fr/VLAN0_LLC_SNAP
nvd.nist.gov/vuln/detail/CVE-2021-27853
github.com/advisories/GHSA-v8jg-p3fp-g968