CVE-2017-12309 in Email Security Appliance
Summary
by MITRE
A vulnerability in the Cisco Email Security Appliance (ESA) could allow an unauthenticated, remote attacker to conduct a HTTP response splitting attack. The vulnerability is due to the failure of the application or its environment to properly sanitize input values. An attacker could exploit this vulnerability by injecting malicious HTTP headers, controlling the response body, or splitting the response into multiple responses. An exploit could allow the attacker to perform cross-site scripting attacks, cross-user defacement, web cache poisoning, and similar exploits. Cisco Bug IDs: CSCvf16705.
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Analysis
by VulDB Data Team • 01/24/2021
The vulnerability identified as CVE-2017-12309 affects the Cisco Email Security Appliance (ESA) and represents a critical security flaw in the application's handling of HTTP requests. This issue stems from inadequate input sanitization mechanisms within the ESA's web interface, creating a pathway for malicious actors to manipulate HTTP responses through carefully crafted inputs. The vulnerability specifically impacts the appliance's ability to properly validate and sanitize user-supplied data before processing HTTP requests, leading to potential exploitation through HTTP response splitting techniques.
The technical implementation of this vulnerability involves the ESA's failure to adequately filter or escape special characters in HTTP header values, particularly those that could be used to inject additional headers or manipulate response boundaries. When an attacker crafts malicious input containing characters that terminate or modify HTTP response structures, the appliance processes this unvalidated data without proper sanitization, allowing the injection of additional HTTP headers into the response stream. This behavior creates opportunities for attackers to manipulate the response content and structure, effectively splitting a single HTTP response into multiple responses or injecting malicious content that can be interpreted by web browsers or caching systems.
The operational impact of CVE-2017-12309 extends beyond simple data manipulation, as it provides attackers with significant capabilities to conduct various forms of web-based attacks. Through successful exploitation, an unauthenticated remote attacker can execute cross-site scripting attacks by injecting malicious script code into HTTP responses, potentially compromising user sessions and accessing sensitive information. The vulnerability also enables cross-user defacement scenarios where attackers can manipulate content displayed to different users, creating confusion and potential data exposure. Additionally, web cache poisoning becomes possible as malicious responses can be cached by intermediary systems, affecting multiple users who subsequently access cached content. This vulnerability aligns with CWE-113, which specifically addresses improper neutralization of CRLF (Carriage Return Line Feed) sequences in HTTP headers, and represents a clear violation of secure coding practices.
The exploitation of this vulnerability follows patterns consistent with the ATT&CK framework's web application attack vectors, particularly focusing on command and control through HTTP response manipulation. Attackers can leverage this flaw to establish persistent access points by injecting malicious content into cached responses or by creating deceptive user interfaces that appear legitimate but contain malicious payloads. The lack of authentication requirements for exploitation makes this vulnerability particularly dangerous as it can be exploited by anyone with network access to the appliance, potentially affecting organizations with limited network segmentation. Organizations implementing the ESA for email security may find their systems vulnerable to attacks that bypass traditional email filtering mechanisms, as the vulnerability operates at the HTTP response level rather than the email content processing level.
Mitigation strategies for CVE-2017-12309 require immediate attention through patch management and configuration hardening measures. Cisco has released software updates addressing this vulnerability through CSCvf16705, and organizations should prioritize deployment of these patches to eliminate the risk of exploitation. Network segmentation and access controls should be implemented to limit direct access to the ESA web interface, reducing the attack surface for potential exploitation. Input validation mechanisms should be strengthened through regular auditing of HTTP header processing and implementation of strict sanitization routines for all user-supplied data. Additionally, organizations should implement monitoring solutions to detect anomalous HTTP response patterns that may indicate exploitation attempts, particularly focusing on unusual header injection patterns or response splitting behaviors that could indicate successful exploitation of this vulnerability.