CVE-2021-20784 in Everything
Summary
by MITRE • 07/14/2021
HTTP header injection vulnerability in Everything all versions except the Lite version may allow a remote attacker to inject an arbitrary script or alter the website that uses the product via unspecified vectors.
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Analysis
by VulDB Data Team • 05/03/2025
This vulnerability represents a critical HTTP header injection flaw that affects various versions of the Everything search software, excluding the Lite version. The vulnerability stems from insufficient input validation and sanitization of user-supplied data that flows into HTTP headers during web application processing. Attackers can exploit this weakness to manipulate HTTP response headers, potentially leading to cross-site scripting attacks, session hijacking, or redirection to malicious websites. The unspecified vectors indicate that the attack surface may encompass multiple entry points within the application's HTTP processing pipeline, making the vulnerability particularly challenging to predict and defend against.
The technical implementation of this vulnerability allows remote attackers to inject malicious content into HTTP headers through crafted input parameters that are not properly escaped or validated before being included in response headers. This type of injection occurs at the application layer where user input is directly concatenated or interpolated into HTTP header fields without adequate security controls. The flaw typically manifests when the application fails to sanitize data that originates from user requests, form submissions, or API calls that ultimately influence HTTP header generation. According to CWE classification, this vulnerability maps to CWE-113: Improper Neutralization of CRLF Sequences in HTTP Headers, which specifically addresses the failure to properly handle carriage return and line feed characters in HTTP headers that can enable header injection attacks.
The operational impact of CVE-2021-20784 extends beyond simple script injection, as it provides attackers with the capability to manipulate web application behavior in multiple ways. Successful exploitation could enable attackers to redirect users to phishing sites, steal session cookies, or inject malicious scripts that execute in the context of the victim's browser. The vulnerability's remote nature means that attackers do not require physical access or local network privileges to exploit the flaw, making it particularly dangerous in publicly accessible web environments. From an attacker's perspective, this vulnerability aligns with ATT&CK technique T1059.007 for Command and Scripting Interpreter: JavaScript, as it enables the execution of malicious JavaScript code through header injection. The attack chain typically involves sending malicious input through web forms, API endpoints, or URL parameters that eventually get processed and injected into HTTP headers, creating a persistent security risk for all affected versions.
Mitigation strategies for this vulnerability should focus on implementing comprehensive input validation and sanitization measures at all points where user data enters the HTTP header processing pipeline. Organizations should deploy proper header escaping mechanisms that prevent carriage return and line feed characters from being interpreted as header delimiters. The recommended approach includes implementing strict validation of all HTTP headers, employing content security policies, and ensuring that user-supplied data is properly encoded before being inserted into HTTP responses. Additionally, application-level firewalls and web application security controls should be configured to detect and block suspicious header injection attempts. Regular security updates and patches should be applied immediately upon availability, as the vulnerability affects multiple versions of the software and requires proactive remediation efforts to maintain security posture. The implementation of automated security testing procedures that specifically target HTTP header injection vulnerabilities should also be integrated into the development lifecycle to prevent similar issues in future releases.