CVE-2008-1544 in Internet Explorer
Summary
by MITRE
The setRequestHeader method of the XMLHttpRequest object in Microsoft Internet Explorer 5.01, 6, and 7 does not block dangerous HTTP request headers when certain 8-bit character sequences are appended to a header name, which allows remote attackers to (1) conduct HTTP request splitting and HTTP request smuggling attacks via an incorrect Content-Length header, (2) access arbitrary virtual hosts via a modified Host header, (3) bypass referrer restrictions via an incorrect Referer header, and (4) bypass the same-origin policy and obtain sensitive information via a crafted request header.
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Analysis
by VulDB Data Team • 06/01/2025
The vulnerability described in CVE-2008-1544 represents a critical security flaw in Microsoft Internet Explorer's implementation of the XMLHttpRequest object that affects versions 5.01, 6, and 7. This issue stems from improper validation of HTTP request headers when specific 8-bit character sequences are appended to header names, creating a dangerous bypass mechanism that undermines fundamental web security controls. The flaw operates at the application layer of the OSI model, specifically within the HTTP protocol handling components of the browser, making it particularly dangerous as it affects the core communication mechanisms that web applications rely upon for secure data exchange.
The technical implementation of this vulnerability exploits the setRequestHeader method's failure to properly sanitize header names that contain 8-bit character sequences, which allows attackers to inject malicious headers that would normally be blocked by security mechanisms. When these malformed header names are processed, the browser's HTTP parser fails to correctly identify and reject dangerous header modifications, enabling attackers to manipulate the underlying HTTP requests in ways that should be impossible. This weakness specifically targets the header validation logic within the XMLHttpRequest object, which is used extensively by web applications to make asynchronous HTTP requests to servers, creating a pathway for attackers to manipulate the request flow at the protocol level.
The operational impact of this vulnerability spans multiple security domains and attack vectors that can be exploited by remote adversaries. The most significant consequences include successful HTTP request splitting and smuggling attacks where attackers can manipulate the Content-Length header to inject additional requests, potentially leading to cross-site scripting or server-side request forgery vulnerabilities. Additionally, the flaw enables virtual host access bypass through modified Host headers, allowing attackers to access content from different virtual hosts that should be restricted. The vulnerability also facilitates referrer restriction bypass via incorrect Referer headers, undermining the security controls that prevent sensitive information leakage between domains. Most critically, this weakness allows bypass of the same-origin policy, which is fundamental to browser security and prevents unauthorized access to resources across different origins, potentially enabling data exfiltration and privilege escalation attacks.
This vulnerability aligns with several CWE classifications including CWE-119 Improper Restriction of Operations within the Bounds of a Memory Buffer, CWE-20 Improper Input Validation, and CWE-444 Insecure HTTP Request Handling, all of which are categorized under the broader ATT&CK framework as part of the T1059 Command and Scripting Interpreter and T1566 Credential Access techniques. The attack surface extends beyond traditional web application security to encompass network-level vulnerabilities that can be exploited through browser-based attack vectors, making this issue particularly dangerous in enterprise environments where multiple web applications and services interact. Organizations should consider implementing network-based mitigations such as web application firewalls and HTTP header filtering, while also ensuring that affected browsers are updated to versions that properly validate HTTP request headers and prevent the injection of malformed header sequences that could lead to these security breaches.
The long-term implications of this vulnerability highlight the critical importance of proper input validation and header sanitization in web browser implementations. This flaw demonstrates how seemingly minor parsing inconsistencies can lead to severe security consequences, emphasizing the need for comprehensive security testing of core browser components. Security practitioners should recognize that this vulnerability represents a failure in the HTTP request processing pipeline that affects not only the specific browser versions mentioned but potentially other implementations that share similar parsing logic, making it essential to monitor for related vulnerabilities and ensure that all HTTP request handling components properly validate and sanitize input before processing. The vulnerability also underscores the importance of maintaining up-to-date browser installations and implementing defense-in-depth strategies that include multiple layers of security controls to protect against similar issues that may arise from improper HTTP protocol handling.