CVE-2025-0825 in cpp-httplib
Summary
by MITRE • 02/04/2025
cpp-httplib version v0.17.3 through v0.18.3 fails to filter CRLF characters ("\r\n") when those are prefixed with a null byte. This enables attackers to exploit CRLF injection that could further lead to HTTP Response Splitting, XSS, and more.
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Analysis
by VulDB Data Team • 08/20/2025
The vulnerability identified as CVE-2025-0825 affects the cpp-httplib library version range from v0.17.3 through v0.18.3, representing a critical security flaw in HTTP response handling mechanisms. This issue stems from inadequate input validation where the library fails to properly sanitize carriage return and line feed characters when they appear in conjunction with null bytes. The flaw specifically manifests when CRLF sequences are prefixed with null byte characters, creating a condition where malicious input can bypass normal filtering mechanisms and be processed as legitimate control characters within HTTP responses.
The technical implementation of this vulnerability resides in the library's handling of string processing and header validation routines. When cpp-httplib processes HTTP requests or responses containing null-byte-prefixed CRLF sequences, the library's sanitization logic fails to recognize these as potentially malicious input patterns. This occurs because the null byte acts as a delimiter that can interfere with standard string parsing functions, allowing the subsequent CRLF characters to be interpreted as actual protocol control sequences rather than data to be filtered out. The vulnerability is classified under CWE-117, which addresses improper output neutralization for logs, and specifically relates to inadequate control character filtering in HTTP protocol implementations.
The operational impact of this vulnerability extends beyond simple data corruption, as it enables sophisticated attack vectors including HTTP response splitting, cross-site scripting, and potential cache poisoning attacks. Attackers can exploit this flaw by crafting malicious input that includes null-byte-prefixed CRLF sequences, which then get embedded into HTTP responses. When a web application using the vulnerable library processes such input, the resulting HTTP responses may contain injected headers or content that can be manipulated by attackers. This creates opportunities for session hijacking, content injection, and other malicious activities that leverage the fundamental trust placed in HTTP response formatting. The vulnerability aligns with ATT&CK technique T1190, which covers exploiting vulnerabilities in web applications, and specifically targets the HTTP protocol layer where such injection attacks are most effective.
Organizations utilizing cpp-httplib within their applications face significant risk exposure from this vulnerability, particularly in environments where user input is processed through HTTP request handlers. The attack surface expands to include any application that accepts user-provided data and processes it through the affected library versions, making this a widespread concern across various web applications and services. Mitigation strategies should prioritize immediate upgrading to version 0.18.4 or later, which includes proper null-byte handling and CRLF filtering mechanisms. Additionally, implementing additional input validation layers, deploying web application firewalls, and conducting thorough code reviews to identify potential injection points can provide defense-in-depth measures. The vulnerability demonstrates the critical importance of proper input sanitization in network protocols and highlights how seemingly minor implementation details in library code can create significant security risks for entire application ecosystems.