A Vulnerability in Exim Mailer Could Allow for Arbitrary Code Execution

ITS Advisory Number: 
2017-120
Date(s) Issued: 
Thursday, November 30, 2017
Subject: 
A Vulnerability in Exim Mailer Could Allow for Arbitrary Code Execution
Overview: 

A vulnerability has been discovered in Exim Mailer, which could allow for arbitrary code execution. Exim Mailer is a message transfer agent on Unix systems that connects to the Internet. Successfully exploiting this vulnerability could allow for arbitrary code execution in the context of the affected application. Depending on the privileges associated with the application, an attacker could install programs; view, change, or delete data; or create new accounts with full user rights. Failed exploitation could result in a denial-of-service condition.

Systems Affected: 
  • Exim Mailer 4.89 and prior

RISK
GOVERNMENT
Large and medium government entities: 
High
Small government entities: 
Medium
BUSINESS
Large and medium business entities: 
High
Small business entities: 
Medium
Home Users: 
N/A
Description: 

A vulnerability has been discovered in Exim Mailer, which could allow for arbitrary code execution. This vulnerability exists due to a use-after-free bug, which could be exploited by an attacker to remotely execute arbitrary code on the SMTP server by crafting a sequence of BDAT commands (CVE-2017-16943).

Successfully exploiting this vulnerability could allow for arbitrary code execution in the context of the affected application. Depending on the privileges associated with the application, an attacker could install programs; view, change, or delete data; or create new accounts with full user rights. Failed exploitation could result in a denial-of-service condition.

Actions: 
  • After appropriate testing, immediately upgrade to the latest version of Exim Mailer.

  • Verify no unauthorized system modifications have occurred on system before applying patch.

  • Apply the principle of Least Privilege to all systems and services.

  • Remind users not to open emails, download attachments, or follow links provided by unknown or untrusted sources.