A vulnerability in the Multipurpose Internet Mail Extensions (MIME) scanner of Cisco AsyncOS Software for Cisco Email Security Appliances (ESA) and Web Security Appliances (WSA) could allow an unauthenticated, remote attacker to bypass configured user filters on the device.

The vulnerability is due to improper error handling of a malformed MIME header in an email attachment.

An attacker could exploit this vulnerability by sending an email with a crafted MIME attachment.

For example, a successful exploit could allow the attacker to bypass user filters configured to prevent executable files from being opened.

The malformed MIME headers may not be RFC compliant but some mail clients could still allow users to access the attachment, which may not have been properly filtered by the device.

There are no workarounds that address this vulnerability.

This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170215-asyncos
A vulnerability in the Multipurpose Internet Mail Extensions (MIME) scanner of Cisco AsyncOS Software for Cisco Email Security Appliances (ESA) and Web Security Appliances (WSA) could allow an unauthenticated, remote attacker to bypass configured user filters on the device.

The vulnerability is due to improper error handling of a malformed MIME header in an email attachment.

An attacker could exploit this vulnerability by sending an email with a crafted MIME attachment.

For example, a successful exploit could allow the attacker to bypass user filters configured to prevent executable files from being opened.

The malformed MIME headers may not be RFC compliant but some mail clients could still allow users to access the attachment, which may not have been properly filtered by the device.

There are no workarounds that address this vulnerability.

This advisory is available at the following link:
https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20170215-asyncos

Security Impact Rating: Medium

CVE: CVE-2017-3827

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