CVE-2015-3183 in SPARC Enterprise Server
Summary
by MITRE
The chunked transfer coding implementation in the Apache HTTP Server before 2.4.14 does not properly parse chunk headers, which allows remote attackers to conduct HTTP request smuggling attacks via a crafted request, related to mishandling of large chunk-size values and invalid chunk-extension characters in modules/http/http_filters.c.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 09/08/2022
The vulnerability identified as CVE-2015-3183 represents a critical flaw in the Apache HTTP Server's handling of chunked transfer encoding, a fundamental HTTP mechanism for transferring data in chunks. This weakness exists in versions prior to 2.4.14 and stems from improper parsing of chunk headers within the http_filters.c module. The vulnerability enables remote attackers to exploit the server's inadequate validation of chunk size values and chunk-extension characters, creating opportunities for sophisticated attack vectors that can compromise the integrity of HTTP communications. The flaw specifically affects how the server processes chunked data streams, which are commonly used in HTTP/1.1 for transferring large amounts of data where the total size is not known in advance.
The technical implementation of this vulnerability resides in the chunked transfer coding parser within Apache's core HTTP processing modules. When the server encounters chunk headers, it fails to properly validate the chunk-size values, particularly when dealing with large numeric values that may exceed normal expectations or trigger integer overflow conditions. Additionally, the parser does not adequately handle invalid chunk-extension characters that may be present in the chunk header, allowing malicious actors to inject malformed data that the server processes incorrectly. This improper handling creates a condition where the server's internal state becomes inconsistent, leading to unpredictable behavior in request processing. The vulnerability is classified under CWE-129 as an Improper Validation of Array Index, as the server fails to validate chunk-size values before processing them, and also relates to CWE-190 as an Integer Overflow or Wraparound, since large chunk-size values can cause arithmetic overflow conditions. The flaw directly impacts the HTTP protocol implementation and can be exploited to manipulate how the server interprets chunked data, potentially allowing attackers to bypass security controls or inject malicious content.
The operational impact of CVE-2015-3183 extends beyond simple request smuggling, as it creates a foundation for more sophisticated attacks that can compromise the entire HTTP communication stack. Attackers can leverage this vulnerability to perform HTTP request smuggling by crafting requests that appear valid to the client but contain malformed chunk headers that the server processes incorrectly. This can lead to request confusion where the server processes multiple requests in an unexpected order, potentially allowing attackers to access restricted resources or bypass authentication mechanisms. The vulnerability is particularly dangerous in environments where Apache serves as a reverse proxy or load balancer, as it can be exploited to manipulate traffic routing or access backend systems that should be protected from direct client access. The attack surface is broad since chunked transfer encoding is commonly used in web applications, especially for large file uploads, streaming content, and APIs that process substantial data payloads. According to ATT&CK framework, this vulnerability maps to T1190 - Proxy, as it can be used to manipulate HTTP traffic through the server's chunked encoding implementation. The exploitation can also be categorized under T1071.004 - Application Layer Protocol: DNS, if the attack involves manipulating DNS responses through the compromised HTTP processing, or T1566 - Phishing, when used in conjunction with social engineering to deliver malicious content through compromised HTTP channels.
Mitigation strategies for CVE-2015-3183 require immediate patching of affected Apache HTTP Server installations to version 2.4.14 or later, where the chunked transfer encoding implementation has been corrected to properly validate chunk headers and handle large chunk-size values. Organizations should also implement network monitoring to detect anomalous HTTP traffic patterns that might indicate exploitation attempts, particularly focusing on requests with unusual chunk header characteristics or unexpected chunk-size values. Additional defensive measures include configuring Apache to disable chunked transfer encoding for specific endpoints where it is not required, implementing proper input validation at the application level, and deploying web application firewalls that can detect and block malformed chunk headers. Security teams should also conduct thorough vulnerability assessments to identify any custom modules or configurations that might be vulnerable to similar chunked encoding issues, as third-party modules may not have received the same security updates as the core Apache server. The fix implemented in version 2.4.14 specifically addresses the improper parsing of chunk headers by introducing stricter validation of chunk-size values and proper handling of invalid chunk-extension characters, ensuring that the server correctly interprets chunked data streams and maintains consistent internal state throughout the processing of HTTP requests.