CVE-2021-27853: Cisco Catalyst 6503-E Firmware

Medium severity, CVSS 4.7. EPSS: 0.8% chance of exploitation in the next 30 days.

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.

Affected products

  • Cisco Catalyst 6503-E Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst 6504-E Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst 6506-E Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst 6509-E Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst 6509-Neb-A Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst 6509-V-E Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst 6513-E Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst 6800ia Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst 6807-Xl Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst 6840-X Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst 6880-X Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst c6816-X-Le Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst c6824-X-Le-40g Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst c6832-X-Le Firmware: version 15.5(01.01.85)sy07 only
  • Cisco Catalyst c6840-X-Le-40g Firmware: version 15.5(01.01.85)sy07 only
  • Cisco IOS XE: version 17.3.3 only; version 15.2(07)e02 only; version 15.2(07)e03 only; version 17.4.1 only; version 17.6.1 only
  • Cisco Meraki MS210 Firmware: affected versions not specified
  • Cisco Meraki MS225 Firmware: affected versions not specified
  • Cisco Meraki MS250 Firmware: affected versions not specified
  • Cisco Meraki MS350 Firmware: affected versions not specified
  • Cisco Meraki MS355 Firmware: affected versions not specified
  • Cisco Meraki MS390 Firmware: affected versions not specified
  • Cisco Meraki MS410 Firmware: affected versions not specified
  • Cisco Meraki MS420 Firmware: affected versions not specified
  • Cisco Meraki MS425 Firmware: affected versions not specified
  • and 71 more

Published 2022-09-27. Last modified 2026-06-17.