CVE-2020-11709 in cpp-httplib
Summary
by MITRE
cpp-httplib through 0.5.8 does not filter \r\n in parameters passed into the set_redirect and set_header functions, which creates possibilities for CRLF injection and HTTP response splitting in some specific contexts.
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Analysis
by VulDB Data Team • 08/05/2025
The vulnerability identified as CVE-2020-11709 affects the cpp-httplib library version 0.5.8 and earlier, presenting a significant security risk through improper input validation in HTTP header handling functions. This flaw resides in the library's implementation of set_redirect and set_header functions, which fail to properly sanitize user-provided parameters before incorporating them into HTTP responses. The absence of input filtering creates an environment where malicious actors can inject carriage return and line feed characters, enabling CRLF injection attacks that can lead to HTTP response splitting vulnerabilities. This issue specifically manifests in contexts where the library processes user-supplied data directly within HTTP header construction, making it particularly dangerous in web applications that utilize this library for HTTP server functionality.
The technical implementation of this vulnerability stems from the library's failure to apply proper input sanitization routines when processing parameters destined for HTTP headers. When developers pass unvalidated user input to the set_redirect or set_header functions, the cpp-httplib library does not perform adequate filtering to remove or escape CRLF characters. This creates a direct pathway for attackers to inject malicious sequences that can manipulate HTTP response headers, potentially enabling various attack vectors including session hijacking, cache poisoning, and cross-site scripting exploits. The vulnerability operates at the application layer of the OSI model and specifically targets HTTP protocol implementations within C++ web applications. According to CWE-113, this represents a weakness in HTTP header processing where insufficient filtering allows for CRLF injection, while the ATT&CK framework categorizes this under T1566.001 - Phishing via Social Engineering, as the vulnerability can be exploited to manipulate HTTP responses and redirect users to malicious destinations.
The operational impact of CVE-2020-11709 extends beyond simple data corruption, as it can enable attackers to manipulate HTTP responses in ways that compromise user sessions and data integrity. When exploited, this vulnerability allows for HTTP response splitting attacks where attackers can inject multiple HTTP responses into a single response, potentially causing browsers to process only the first response while ignoring subsequent malicious responses. This can lead to session fixation, where attackers can establish a user session with predetermined credentials, or cache poisoning attacks where malicious content is cached and served to other users. The vulnerability is particularly concerning in web applications that rely on cpp-httplib for handling user requests and responses, as it can be exploited without requiring elevated privileges or specialized tools. Attackers can leverage this weakness to redirect users to malicious websites, inject malicious content into responses, or manipulate application behavior through header manipulation, making it a critical concern for applications handling sensitive user data or implementing authentication mechanisms.
Mitigation strategies for CVE-2020-11709 should focus on immediate library updates to version 0.5.9 or later, where the vulnerability has been addressed through proper input validation and sanitization of parameters passed to set_redirect and set_header functions. Organizations should implement comprehensive input validation at multiple layers of their application architecture, ensuring that all user-provided data is sanitized before being processed by any HTTP header manipulation functions. The implementation of proper HTTP header validation routines, including the removal or encoding of CRLF characters, should be integrated into application security testing protocols. Additionally, security teams should conduct thorough code reviews to identify any other instances where similar vulnerabilities might exist within the application's HTTP handling components, particularly focusing on functions that process user input for header construction. Network monitoring solutions should be configured to detect unusual HTTP response patterns that might indicate exploitation attempts, while web application firewalls can be deployed to filter out known malicious CRLF injection patterns. The remediation process should also include updating security documentation to reflect proper handling of HTTP headers and establishing secure coding practices that prevent similar issues from occurring in future development cycles, aligning with industry standards such as OWASP Top Ten and NIST Cybersecurity Framework recommendations for secure software development practices.