CVE-2011-1895 in Forefront Unified Access Gateway
Summary
by MITRE
CRLF injection vulnerability in Microsoft Forefront Unified Access Gateway (UAG) 2010 Gold, Update 1, Update 2, and SP1 allows remote attackers to inject arbitrary HTTP headers, and conduct HTTP response splitting attacks and cross-site scripting (XSS) attacks, via unspecified vectors, aka "ExcelTable Response Splitting XSS Vulnerability."
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Analysis
by VulDB Data Team • 03/19/2021
The CVE-2011-1895 vulnerability represents a critical CRLF injection flaw within Microsoft Forefront Unified Access Gateway 2010 across multiple update versions and service packs. This vulnerability specifically affects the ExcelTable component of the UAG system, creating a pathway for remote attackers to manipulate HTTP responses through carefully crafted input sequences. The vulnerability stems from insufficient validation of user-supplied data within the response handling mechanism, allowing malicious actors to inject carriage return line feed sequences that can alter the HTTP header structure.
The technical exploitation of this vulnerability leverages the fundamental weakness in input sanitization processes where CRLF characters are not properly escaped or filtered from user-controllable parameters. When the UAG processes requests containing malicious CRLF sequences, these characters are interpreted as HTTP header terminators rather than normal input data, enabling attackers to inject arbitrary HTTP headers into the response stream. This behavior aligns with CWE-113, which specifically addresses improper neutralization of CRLF characters in HTTP headers, making it a direct implementation of this well-known vulnerability pattern.
The operational impact of this vulnerability extends beyond simple header injection to encompass serious security implications including HTTP response splitting attacks and cross-site scripting exploitation. HTTP response splitting occurs when an attacker injects multiple HTTP responses within a single HTTP transaction, potentially allowing them to bypass security controls, cache poisoning, or redirect users to malicious content. The XSS component arises because the injected headers can contain script payloads that execute in the context of the victim's browser, particularly when the malicious response is rendered in a web interface that displays the injected data without proper sanitization.
This vulnerability affects Microsoft Forefront Unified Access Gateway 2010 deployments including Gold, Update 1, Update 2, and SP1 versions, indicating a widespread exposure across the product lifecycle. The attack surface is particularly concerning given that UAG serves as a unified access gateway that typically handles sensitive authentication and authorization flows, making it a prime target for attackers seeking to escalate privileges or gain unauthorized access to protected resources. The unspecified attack vectors suggest that multiple input points within the ExcelTable functionality could be exploited, increasing the potential attack surface and making comprehensive patching more challenging.
Security professionals should consider this vulnerability in the context of broader attack patterns documented in the MITRE ATT&CK framework, particularly within the execution and command and control phases where HTTP response manipulation can enable further exploitation. The vulnerability's classification under CWE-113 places it within the category of HTTP header injection flaws that have been consistently exploited in enterprise environments, with similar patterns observed in other Microsoft products and web applications. Organizations should implement immediate mitigation strategies including input validation, header sanitization, and application-level filtering to prevent CRLF sequences from being processed as part of user-supplied content, while also prioritizing the deployment of official Microsoft security patches that address the root cause of the vulnerability.