Summary

• A vulnerability in the base64d function in the SMTP listener component of Exim could allow an unauthenticated, remote attacker to execute arbitrary code on a targeted system.
  
  The vulnerability is due to insufficient validation of user-supplied input by the affected system. An attacker could exploit this vulnerability by submitting a crafted message to the affected system. A successful exploit could cause a buffer overflow condition, which could allow the attacker to execute arbitrary code on the system.
  
  Exim.org has confirmed the vulnerability and released a software patch.

Analysis

• To exploit this vulnerability, the attacker must send a crafted message to the targeted system, making exploitation more difficult in environments that restrict network access from untrusted sources.

Safeguards

• Administrators are advised to apply the appropriate updates.
  
  Administrators are advised to allow only trusted users to have network access.
  
  Administrators may consider using IP-based access control lists (ACLs) to allow only trusted systems to access the affected systems.
  
  Administrators are advised to monitor affected systems.

Vendor Announcements

• Exim.org has released a git commit at the following link: CVE-2018-6789
  
  FreeBSD has released a VuXML document at the following link: exim -- a buffer overflow vulnerability, remote code execution

Fixed Software

• Exim.org has released a software patch at the following link: Fix base64d() buffer size (CVE-2018-6789)
  
  FreeBSD has released ports collection updates at the following link: Ports Collection Index
  

Revision History

• Version	Description	Section	Date
  3	Cisco has updated this alert to include additional Exim versions that are affected by the Exim base64d function buffer overflow arbitrary code execution vulnerability.	Affected Products	2018-March-16
  2	Exim.org has released a patch to address the Exim base64d function buffer overflow arbitrary code execution vulnerability. FreeBSD has released a VuXML document and ports collection updates to address this vulnerability.	Header, Summary, Vendor Announcements, Fixed Software, Affected Products	2018-February-12
  1	Initial public release.	—	2018-February-09

  Show Less

Affected Products

• The security vulnerability applies to the following combinations of products.
  
  

  Primary Products
  GNU Public License	Exim	4.44 (Base) | 4.50 (Base) | 4.51 (Base) | 4.52 (Base) | 4.53 (Base) | 4.54 (Base) | 4.60 (Base) | 4.61 (Base) | 4.62 (Base) | 4.63 (Base) | 4.64 (Base) | 4.65 (Base) | 4.66 (Base) | 4.67 (Base) | 4.68 (Base) | 4.69 (Base) | 4.70 (Base) | 4.71 (Base) | 4.72 (Base) | 4.73 (Base) | 4.74 (Base) | 4.75 (Base) | 4.76 (Base) | 4.77 (Base) | 4.80 (Base, .1) | 4.82 (Base) | 4.83 (Base) | 4.84 (Base) | 4.85 (Base) | 4.86 (Base) | 4.87 (Base) | 4.88 (Base) | 4.89 (Base) | 4.90 (Base)

  Associated Products
  FreeBSD Project	FreeBSD	10.2 (.0) | 10.3 (.0) | 11.0 (.0) | 11.1 (.0) | 10.4 (.0) | 8.0 (Base) | 8.1 (Base) | 8.2 (Base) | 8.3 (Base) | 8.4 (Base) | 9.0 (Base) | 9.1 (Base) | 9.2 (Base) | 9.3 (Base) | 10.0 (.0) | 10.1 (.0)