CVE-2021-34739: Cisco CBS250-16p-2g Firmware

High severity, CVSS 8.1. EPSS: 1.7% chance of exploitation in the next 30 days.

A vulnerability in the web-based management interface of multiple Cisco Small Business Series Switches could allow an unauthenticated, remote attacker to replay valid user session credentials and gain unauthorized access to the web-based management interface of an affected device. This vulnerability is due to insufficient expiration of session credentials. An attacker could exploit this vulnerability by conducting a man-in-the-middle attack against an affected device to intercept valid session credentials and then replaying the intercepted credentials toward the same device at a later time. A successful exploit could allow the attacker to access the web-based management interface with administrator privileges.

Affected products

  • Cisco CBS250-16p-2g Firmware: up to and including 3.1
  • Cisco CBS250-16t-2g Firmware: up to and including 3.1
  • Cisco CBS250-24fp-4g Firmware: up to and including 3.1
  • Cisco CBS250-24fp-4x Firmware: up to and including 3.1
  • Cisco CBS250-24p-4g Firmware: up to and including 3.1
  • Cisco CBS250-24p-4x Firmware: up to and including 3.1
  • Cisco CBS250-24pp-4g Firmware: up to and including 3.1
  • Cisco CBS250-24t-4g Firmware: up to and including 3.1
  • Cisco CBS250-24t-4x Firmware: up to and including 3.1
  • Cisco CBS250-48p-4g Firmware: up to and including 3.1
  • Cisco CBS250-48p-4x Firmware: up to and including 3.1
  • Cisco CBS250-48pp-4g Firmware: up to and including 3.1
  • Cisco CBS250-48t-4g Firmware: up to and including 3.1
  • Cisco CBS250-48t-4x Firmware: up to and including 3.1
  • Cisco CBS250-8fp-E-2g Firmware: up to and including 3.1
  • Cisco CBS250-8p-E-2g Firmware: up to and including 3.1
  • Cisco CBS250-8pp-D Firmware: up to and including 3.1
  • Cisco CBS250-8pp-E-2g Firmware: up to and including 3.1
  • Cisco CBS250-8t-D Firmware: up to and including 3.1
  • Cisco CBS250-8t-E-2g Firmware: up to and including 3.1
  • Cisco CBS350-12np-4x Firmware: up to and including 3.1
  • Cisco CBS350-12xs Firmware: up to and including 3.1
  • Cisco CBS350-12xt Firmware: up to and including 3.1
  • Cisco CBS350-16fp-2g Firmware: up to and including 3.1
  • Cisco CBS350-16p-2g Firmware: up to and including 3.1
  • and 184 more

Published 2021-11-04. Last modified 2026-06-17.