CVE-2026-66753 in tiny-http
Summary
by MITRE • 07/28/2026
tiny-http through 0.12.0 contains an HTTP header injection vulnerability that allows attackers to inject carriage return (0x0D) and line feed (0x0A) bytes into HTTP header values on both request and response sides due to insufficient validation in header parsing and serialization. Attackers can exploit this injection primitive to perform response splitting, cache poisoning, session fixation via Set-Cookie injection, security header override, and request smuggling against line-feed-tolerant backends.
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Analysis
by VulDB Data Team • 07/28/2026
The tiny-http library version 0.12.0 and earlier contains a critical HTTP header injection vulnerability that stems from inadequate input validation during header parsing and serialization processes. This flaw exists in both request and response handling mechanisms, creating a significant security risk for applications that rely on the library for HTTP communication. The vulnerability specifically permits attackers to inject carriage return characters 0x0D and line feed characters 0x0A into HTTP header values, effectively bypassing normal header validation controls. This injection capability originates from the library's failure to properly sanitize header content before processing, creating an attack surface that can be exploited across multiple threat vectors.
The technical implementation of this vulnerability allows attackers to manipulate HTTP headers through carefully crafted input sequences that contain the forbidden control characters. When the library processes these malformed headers, it fails to strip or escape the injected CR/LF bytes, leading to header value corruption that can have cascading effects throughout the HTTP communication stack. The flaw manifests during both incoming request parsing and outgoing response construction, making it particularly dangerous as attackers can target either side of the communication channel. This dual-sided vulnerability means that an attacker could inject malicious headers in requests sent to a server or responses received from a client, expanding the potential attack scenarios significantly.
From an operational impact perspective, this vulnerability enables several sophisticated attack patterns that can severely compromise system security and integrity. Response splitting becomes possible as attackers can inject additional HTTP responses into the communication stream, potentially leading to cache poisoning attacks where malicious content is cached and served to other users. Session fixation vulnerabilities can be exploited through Set-Cookie header injection, allowing attackers to hijack user sessions by injecting malicious cookie values that persist across multiple requests. Security header override attacks become feasible, where critical security headers like Content-Security-Policy or X-Frame-Options can be manipulated to weaken application defenses. Additionally, request smuggling against line-feed-tolerant backends becomes possible, enabling attackers to craft HTTP requests that appear legitimate to the client but are interpreted differently by backend servers, potentially bypassing security controls designed to prevent such attacks.
The exploitation of this vulnerability aligns with several established threat patterns documented in cybersecurity frameworks including CWE-113 for improper neutralization of CRLF characters and ATT&CK techniques related to HTTP request smuggling and cache poisoning. This vulnerability is particularly concerning because it affects the fundamental HTTP processing capabilities of applications using tiny-http, making it a critical security concern for web applications, APIs, and services that rely on this library for their HTTP communication infrastructure. Organizations utilizing this library should immediately evaluate their attack surface and implement immediate mitigations to prevent exploitation attempts.
Mitigation strategies should focus on updating to patched versions of the tiny-http library where available, implementing comprehensive input validation at all HTTP header processing points, and deploying additional defensive controls such as web application firewalls that can detect and block malformed header sequences. Network-level protections including strict header validation rules and monitoring for unusual header patterns can provide additional layers of defense. Organizations should also conduct thorough security assessments to identify any applications or services that may be vulnerable to this attack vector, particularly those handling sensitive user data or operating in environments where session management and access controls are critical. The vulnerability demonstrates the importance of proper input sanitization in HTTP libraries and highlights the potential for seemingly minor parsing flaws to create significant security implications across entire application ecosystems.