CVE-2015-4278 in Email Security Appliance
Summary
by MITRE
Cisco Email Security Appliance (ESA) devices with software 8.5.6-106 and 9.5.0-201 allow remote attackers to cause a denial of service (per-domain e-mail reception outage) by placing malformed DMARC policy data in DNS TXT records for a domain, aka Bug ID CSCuv14806.
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Analysis
by VulDB Data Team • 06/03/2022
The Cisco Email Security Appliance ESA vulnerability CVE-2015-4278 represents a critical denial of service weakness that specifically targets the email security infrastructure of enterprise organizations. This vulnerability affects ESA devices running software versions 8.5.6-106 and 9.5.0-201 and stems from improper handling of malformed DMARC policy data within DNS TXT records. The flaw operates at the intersection of DNS resolution and email security processing, where the appliance fails to properly validate or sanitize DMARC policy information before attempting to process email traffic for affected domains. This vulnerability is particularly dangerous because it can be exploited remotely without authentication, allowing attackers to disrupt email reception for entire domains through manipulation of publicly accessible DNS records.
The technical implementation of this vulnerability resides in the ESA's DMARC policy parsing mechanism, which lacks adequate input validation for DNS TXT record data. When the appliance encounters malformed DMARC policy data during DNS resolution for email domain verification, the system experiences a critical processing failure that results in complete email reception outages for the affected domain. This behavior aligns with CWE-129 Input Validation and CWE-20 Improper Input Validation, as the system fails to properly validate the structure and content of the DMARC policy data before processing. The vulnerability operates through the standard DNS resolution process where the ESA queries TXT records for domain DMARC policies, but fails to handle malformed data gracefully, leading to system instability and service disruption.
The operational impact of CVE-2015-4278 extends beyond simple service interruption to represent a significant threat to enterprise email infrastructure reliability and business continuity. Organizations utilizing affected ESA appliances face potential complete email service outages for targeted domains, which can severely impact communication workflows, customer service operations, and internal business processes that depend on email delivery. The remote exploitation capability means that attackers can orchestrate these outages from anywhere on the internet without requiring physical access or network credentials, making the vulnerability particularly attractive for denial of service attacks. This vulnerability also represents a potential vector for broader network disruption when considering that many organizations rely on email as a primary communication channel for critical business functions.
Security professionals should recognize this vulnerability as a potential indicator of broader DNS-based attack patterns that align with techniques described in the MITRE ATT&CK framework under T1071.004 Application Layer Protocol DNS and T1499.004 Endpoint Denial of Service. The remediation approach should focus on immediate software patching to address the DMARC policy parsing flaw, along with implementing additional DNS monitoring and validation mechanisms. Organizations should also consider implementing network segmentation to limit the potential impact of such attacks and establish monitoring procedures for anomalous DNS record changes that could indicate attempted exploitation. The vulnerability highlights the importance of robust input validation in security appliances and demonstrates how seemingly benign DNS record manipulation can result in catastrophic service disruption.