CVE-2015-5739 in Google
Summary
by MITRE
The net/http library in net/textproto/reader.go in Go before 1.4.3 does not properly parse HTTP header keys, which allows remote attackers to conduct HTTP request smuggling attacks via a space instead of a hyphen, as demonstrated by "Content Length" instead of "Content-Length."
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Analysis
by VulDB Data Team • 01/04/2023
The vulnerability identified as CVE-2015-5739 resides within the net/http library of the Go programming language, specifically in the net/textproto/reader.go file. This flaw represents a critical security issue that affects Go versions prior to 1.4.3, where the HTTP header parsing mechanism fails to properly validate and normalize header keys. The vulnerability stems from the library's inability to correctly process HTTP header keys that contain spaces instead of the standard hyphen character, creating a potential attack vector for malicious actors seeking to exploit HTTP request smuggling techniques.
The technical nature of this vulnerability allows attackers to manipulate HTTP header parsing by substituting spaces for hyphens in header field names, such as using "Content Length" instead of the standard "Content-Length" format. This parsing inconsistency occurs because the Go library does not enforce strict header key validation, enabling attackers to craft malformed headers that may be interpreted differently by various HTTP servers and proxies. The flaw exploits the fact that some systems treat headers with spaces differently than those with proper hyphens, creating opportunities for request smuggling where the server's interpretation of header boundaries becomes ambiguous.
The operational impact of this vulnerability extends beyond simple header parsing issues, as it enables sophisticated HTTP request smuggling attacks that can bypass security controls and potentially lead to data leakage or unauthorized access. Attackers can leverage this weakness to manipulate how HTTP requests are processed by intermediaries such as load balancers, proxies, and web application firewalls, potentially allowing them to inject malicious content or bypass authentication mechanisms. The vulnerability particularly affects systems that rely on Go-based web servers or applications that process HTTP headers, making it a significant concern for organizations using Go in production environments.
Security professionals should consider this vulnerability in the context of CWE-20, which addresses improper input validation, and its alignment with ATT&CK technique T1071.301 for application layer protocol manipulation. The issue demonstrates how seemingly minor parsing inconsistencies can create substantial security risks when combined with HTTP protocol behaviors. Organizations should prioritize updating their Go installations to version 1.4.3 or later, implementing proper header validation at application level, and monitoring for suspicious header patterns in their HTTP traffic logs. Additionally, network security teams should configure proxies and firewalls to normalize header formats and detect potential exploitation attempts. The vulnerability serves as a reminder of the critical importance of proper input validation and header normalization in web application security, particularly in languages and libraries that handle HTTP protocol interactions.