01 Record
CVE-2021-27853
L2 network filtering can be bypassed using stacked VLAN0 and LLC/SNAP headers
MediumPUBLISHEDCNA: certcc
CNA base score4.7 CVSS v3.xCVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
02 Description
L2 network filtering can be bypassed using stacked VLAN0 and LLC/SNAP headers
03 Exploitation and scoring
- Exploitation
- Assessed, none found. CISA's assessment recorded neither public exploit code nor evidence of exploitation when it was made.
- SSVC decision
- ExploitationnoneCISA recorded no public exploit code and no evidence of exploitation.
- AutomatablenoAt least one step from reconnaissance to exploitation cannot be reliably automated.
- Technical ImpactpartialSuccessful exploitation gives limited control of the vulnerable component.
- EPSS probability
- 0.81% probability of exploitation activity in the next 30 days.
- EPSS percentile
- Equal to or higher than the score of 56.7% of scored records. A rank, not a probability.
- NVD base score
- 4.7 (CVSS v3.x), scored by the NVD independently of the CNA.
- NVD CVSS vector
- CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
- NVD analysis status
- Modified. NVD last modified this record on 2026-06-17.
- Red Hat severity
- Moderate. Red Hat's rating for its own products, not a CVSS rating.
Exploit-prediction scores from FIRST. Independent scoring and analysis status from the NVD. Vendor severity from Red Hat. Exploitation assessment and catalog membership from CISA.
04 Metadata
- Published
- 2022-09-27 17:55Z4 YR AGO
- Last updated
- 2025-11-04 19:12Z11 MO AGO
- Reserved
- 2021-03-01
- Assigning CNA
- certcc
- Record state
- PUBLISHED
- Severity
- Medium (CVSS 4.7)
- CNA CVSS vector
- CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
- Weaknesses
- CWE-290Authentication Bypass by SpoofingBase
- Data version
- 5.2
- Document digest
- 2a75d0dd18cb76901b2b25ec79eb4bff6fe971804a52765d385117d1cc524bb4
05 Affected products
VendorProductVersionsPlatforms
06 References
- datatracker.ietf.orghttps://datatracker.ietf.org/doc/draft-ietf-v6ops-ra-guard/08/
- standards.ieee.orghttps://standards.ieee.org/ieee/802.2/1048/
- standards.ieee.orghttps://standards.ieee.org/ieee/802.1Q/10323/
- tools.cisco.com20220927 Vulnerabilities in Layer 2 Network Security Controls Affecting Cisco Products: September 2022https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-VU855201-J3z8CKTX
- kb.cert.orghttps://kb.cert.org/vuls/id/855201
- blog.champtar.frhttps://blog.champtar.fr/VLAN0_LLC_SNAP/
- www.kb.cert.orghttps://www.kb.cert.org/vuls/id/855201