A vulnerability in the Sender Policy Framework (SPF) functionality of Cisco AsyncOS Software for Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to bypass the configured user filters on an affected device. The vulnerability exists because the affected software insufficiently validates certain incoming SPF messages. An attacker could exploit this vulnerability by sending a custom SPF packet to an affected devices. There are no workarounds that address this vulnerability. The advisory is available at the following link:https://tools.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20191002-esa-bypass.”]
Source: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20191002-esa-bypass