CVE-2017-14063 in Async Http Client
Summary
by MITRE
Async Http Client (aka async-http-client) before 2.0.35 can be tricked into connecting to a host different from the one extracted by java.net.URI if a '?' character occurs in a fragment identifier. Similar bugs were previously identified in cURL (CVE-2016-8624) and Oracle Java 8 java.net.URL.
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Analysis
by VulDB Data Team • 12/27/2022
The Async Http Client library represents a widely-used asynchronous HTTP client implementation for java applications that facilitates non-blocking network operations. This particular vulnerability affects versions prior to 2.0.35 and demonstrates a critical flaw in URI parsing behavior that can lead to unintended network connections. The vulnerability stems from how the library processes URI fragments containing question marks, creating a scenario where the client connects to a different host than originally intended. This type of issue falls under the category of improper handling of URI components and can be classified as a variant of CWE-601 URL Redirection to Untrusted Site vulnerability.
The technical flaw manifests when the async-http-client library encounters a URI with a fragment identifier containing a '?' character. The java.net.URI class normally handles fragment parsing according to RFC 3986 standards, but the async-http-client implementation fails to properly isolate the fragment component from the rest of the URI structure. When a '?' appears within a fragment, the library's parsing logic becomes confused about which portion of the URI represents the actual host address versus the fragment data. This confusion causes the client to establish connections to a host derived from the fragment rather than the intended target host, effectively enabling a form of HTTP request smuggling or man-in-the-middle attack vector.
The operational impact of this vulnerability extends beyond simple connection confusion, as it can enable attackers to redirect network traffic to unintended destinations. An attacker could craft malicious URIs that appear legitimate to the application but cause the client to connect to malicious hosts specified within the fragment portion of the URI. This behavior creates potential security risks including data exfiltration, credential theft, or redirection to phishing sites. The vulnerability is particularly concerning in applications that process user-provided URLs or that rely on third-party services for URL validation, as it can bypass traditional security controls that assume proper URI parsing.
Organizations using affected versions of async-http-client should immediately upgrade to version 2.0.35 or later to mitigate this vulnerability. The fix implemented in version 2.0.35 addresses the URI parsing logic to properly separate fragment components from host information, ensuring that connection attempts are made to the intended destination. Additional mitigations include implementing strict URI validation at application boundaries, monitoring for unusual connection patterns, and configuring network-level controls to restrict outbound connections to known trusted domains. This vulnerability aligns with ATT&CK technique T1071.004 for Application Layer Protocol: DNS and demonstrates how seemingly minor parsing issues can create significant security implications. The issue also relates to CWE-444 and CWE-601, highlighting the importance of proper input validation and secure URI handling in networked applications.