CVE-2019-19680 in Protection Server Email Firewall
Summary
by MITRE
A file-extension filtering vulnerability in ProofPoint Protection Server Email Firewall through 8.10 allows attackers to bypass protection mechanisms (related to extensions, MIME types, virus detection, and journal entries for transmitted files) by sending malformed (not RFC compliant) multipart email.
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Analysis
by VulDB Data Team • 01/14/2020
The CVE-2019-19680 vulnerability represents a critical file extension filtering weakness within ProofPoint Protection Server Email Firewall version 8.10 and earlier. This flaw operates at the email processing layer where the system fails to properly validate file extensions within multipart email messages, creating a pathway for attackers to circumvent security controls designed to block malicious attachments. The vulnerability specifically targets the email firewall's ability to enforce content restrictions based on file extensions, MIME types, and virus detection parameters, effectively undermining the protective mechanisms that organizations rely upon to prevent malware delivery through email channels.
The technical exploitation of this vulnerability occurs through the manipulation of multipart email structures that do not conform to RFC standards. Attackers can craft emails with malformed multipart boundaries or improperly formatted content disposition headers that cause the ProofPoint firewall to incorrectly parse file extensions. This parsing error allows malicious files to be delivered through the email system with extensions that would normally be blocked by the firewall's content filtering rules. The vulnerability extends beyond simple file extension bypass to affect virus detection mechanisms, journal entry logging, and overall email content inspection processes. The system's failure to properly validate multipart email structures creates a parsing inconsistency where legitimate security controls become ineffective against crafted malicious payloads.
From an operational impact perspective, this vulnerability presents a significant risk to organizations relying on ProofPoint Protection Server for email security. The bypass mechanism allows attackers to deliver potentially harmful files that would normally be blocked by the firewall's extension filtering rules, including executable files, script files, and other malicious content types. The vulnerability affects multiple security layers within the email protection system, potentially compromising virus detection capabilities, altering journaling behavior for transmitted files, and creating blind spots in content inspection. Organizations may experience false security assurances from their email protection systems while simultaneously allowing malicious content to pass through undetected. The impact extends to compliance requirements and security monitoring systems that depend on accurate email content filtering and logging behaviors.
The vulnerability aligns with CWE-20 Improper Input Validation, specifically addressing weaknesses in how email content is parsed and validated within security appliances. This weakness creates a pathway for attackers to exploit the difference between standard RFC-compliant email processing and the system's handling of malformed content, enabling the bypass of multiple security controls simultaneously. The attack pattern follows principles outlined in the MITRE ATT&CK framework under T1190 Exploit Public-Facing Application, where an attacker targets a specific vulnerability in email security infrastructure to gain unauthorized access to systems through email-based delivery methods. Organizations should implement immediate mitigations including firmware updates to the latest ProofPoint Protection Server versions, enhanced email content inspection rules, and additional security controls to compensate for the bypass capability. Network segmentation, additional email scanning solutions, and enhanced monitoring of email traffic patterns can help detect and prevent exploitation attempts while awaiting official patches.