Rule Category

SERVER-MAIL -- Snort has detected traffic exploiting vulnerabilities in mail servers (such as Exchange, Courrier). These are different from protocol traffic, as this deals with the traffic going to the mail server itself.

Alert Message

SERVER-MAIL EHLO user overflow attempt

Rule Explanation

This event is generated when an attacker attempts to send an overly long EHLO SMTP message, used to exploit an off-by-one vulnerability present in the Exim mail transfer agent. Impact: Attempted Administrator Privilege Gain Details: Rule checks for overly long EHLO SMTP messages used to exploit an off-by-one vulnerability present in the Exim mail transfer agent. Ease of Attack: Simple

What To Look For

Known Usage

No public information

False Positives

No known false positives

Contributors

Cisco Talos Intelligence Group

MITRE ATT&CK Framework

Tactic:

Technique:

For reference, see the MITRE ATT&CK vulnerability types here: https://attack.mitre.org

CVE

CVE Additional Information

CVE-2018-6789
An issue was discovered in the base64d function in the SMTP listener in Exim before 4.90.1. By sending a handcrafted message, a buffer overflow may happen. This can be used to execute code remotely.
Details
Severity Base Score9.8
Impact Score5.9 Exploit Score3.9
Confidentiality ImpactHIGH Integrity ImpactHIGH
Availability ImpactHIGH Access Vector
Authentication Ease of Access
CVE-2019-16928
Exim 4.92 through 4.92.2 allows remote code execution, a different vulnerability than CVE-2019-15846. There is a heap-based buffer overflow in string_vformat in string.c involving a long EHLO command.
Details
SeverityHIGH Base Score7.5
Impact Score6.4 Exploit Score10.0
Confidentiality ImpactPARTIAL Integrity ImpactPARTIAL
Availability ImpactPARTIAL Access VectorNETWORK
AuthenticationNONE Ease of AccessLOW