A vulnerability in the Simple Mail Transfer Protocol (SMTP) header filtering functionality of Cisco AsyncOS Software for Cisco Email Security Appliances (ESA) could allow an unauthenticated, remote attacker to bypass configured user filters on the device. The vulnerability is due to improper handling of a malformed SMTP header in an email received on an affected device. An attacker could exploit this vulnerability by sending an email containing a crafted SMTP header. A successful exploit could allow the attacker to bypass the configured ESA content filtering mechanisms, allowing some email clients to display the malformed header information from the email message. This advisory is available at the following link: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-20171129-esa
For information about fixed software releases, consult the Cisco bug ID(s) at the top of this advisory.
When considering software upgrades, customers are advised to regularly consult the advisories for Cisco products, which are available from the Cisco Security Advisories and Alerts page, to determine exposure and a complete upgrade solution.
In all cases, customers should ensure that the devices to be upgraded contain sufficient memory and confirm that current hardware and software configurations will continue to be supported properly by the new release. If the information is not clear, customers are advised to contact the Cisco Technical Assistance Center (TAC) or their contracted maintenance providers.
The Cisco Product Security Incident Response Team (PSIRT) is not aware of any public announcements or malicious use of the vulnerability that is described in this advisory.
This vulnerability was reported to the Cisco PSIRT by Mai Ngoc Duong.
To learn about Cisco security vulnerability disclosure policies and publications, see the Security Vulnerability Policy. This document also contains instructions for obtaining fixed software and receiving security vulnerability information from Cisco.
| Version | Description | Section | Status | Date |
|---|---|---|---|---|
| 1.4 | Set Workarounds to Yes in advisory header. | Header | Final | 2017-December-12 |
| 1.3 | Added workaround information. | Workarounds | Final | 2017-December-12 |
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