CVE-2019-1844 in Email Security Appliance
Summary
by MITRE
A vulnerability in certain attachment detection mechanisms of the Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to bypass the filtering functionality of an affected device. The vulnerability is due to improper detection of certain content sent to an affected device. An attacker could exploit this vulnerability by sending certain file types without Content-Disposition information to an affected device. A successful exploit could allow an attacker to send messages that contain malicious content to users.
If you want to get best quality of vulnerability data, you may have to visit VulDB.
Analysis
by VulDB Data Team • 09/12/2023
The vulnerability identified as CVE-2019-1844 affects Cisco Email Security Appliance (ESA) systems and represents a critical flaw in the device's attachment detection mechanisms. This weakness stems from insufficient validation of file content characteristics during email processing, specifically when handling messages lacking proper Content-Disposition headers. The vulnerability operates at the protocol level where email security appliances typically enforce strict content filtering policies to prevent malicious attachments from reaching end users. When the ESA fails to properly identify certain file types due to missing or malformed Content-Disposition information, it creates a bypass opportunity for attackers to circumvent the device's intended security controls.
The technical implementation of this vulnerability exploits the ESA's content detection algorithms which rely on specific headers and content characteristics to classify and filter email attachments. Without Content-Disposition information, the system cannot properly determine the nature of the attached file, leading to a failure in applying appropriate security checks and filtering rules. This flaw demonstrates a classic weakness in input validation where the system assumes certain header fields will always be present, creating a path for malicious content to slip through security controls. The vulnerability specifically targets the device's ability to perform proper attachment analysis, which is a fundamental security function designed to prevent the delivery of potentially harmful email content to users.
Operationally, this vulnerability presents a severe risk to organizations relying on Cisco ESA for email security, as it allows unauthenticated remote attackers to bypass critical filtering mechanisms without requiring any credentials or privileged access. The impact extends beyond simple content delivery, as attackers can craft messages containing malicious attachments that would normally be blocked by the appliance's security policies. This creates a significant attack surface where threat actors can deliver phishing emails, malware payloads, or other malicious content directly to users' inboxes. The vulnerability essentially undermines the core security posture of the email infrastructure, potentially leading to data breaches, system compromises, and other security incidents that could affect entire organizations.
Organizations should implement immediate mitigations including applying the latest Cisco security patches and updates to address the vulnerability in the ESA device. Network administrators should also consider implementing additional email security controls such as enhanced content filtering rules, sandboxing mechanisms, and behavioral analysis systems that can detect anomalous email patterns even when traditional attachment detection fails. The vulnerability aligns with CWE-20, which describes improper input validation, and represents a technique that could be categorized under ATT&CK tactic TA0005 (Defense Evasion) and technique T1070.004 (File Deletion) when attackers use this bypass to deliver malicious content that may later be used for more sophisticated attacks. Additionally, implementing network segmentation and email encryption protocols can provide additional layers of protection against exploitation of this vulnerability.