CVE-2026-54163 in secure_headers
Summary
by MITRE • 07/18/2026
secure_headers manages application of security headers with many safe defaults. Prior to 7.3.0, secure_headers builds the Content-Security-Policy value by stitching directives with ; separators, and build_sandbox_list_directive, build_media_type_list_directive, and build_report_to_directive interpolate caller-supplied strings without scrubbing ;, \r, or \n. When untrusted input reaches SecureHeaders.override_content_security_policy_directives or append APIs for :sandbox, :plugin_types, or :report_to, an attacker can inject a CSP directive such as script-src 'unsafe-inline' * before the legitimate script-src, enabling XSS reachability through these sinks or CSP report exfiltration. This issue is fixed in version 7.3.0.
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Analysis
by VulDB Data Team • 07/18/2026
The secure_headers gem represents a critical security vulnerability that affects web application security configurations through improper handling of user-supplied input in Content-Security-Policy header construction. This vulnerability exists in versions prior to 7.3.0 and specifically targets the way the library processes directive values, creating potential attack vectors through insecure string interpolation mechanisms. The flaw stems from inadequate sanitization of caller-provided data when constructing security headers, particularly affecting the sandbox, plugin_types, and report_to directives where unescaped semicolons, carriage returns, and line feeds can be injected into the policy string.
The technical implementation of this vulnerability exploits the build_sandbox_list_directive, build_media_type_list_directive, and build_report_to_directive methods which fail to properly sanitize input before concatenating it into security policy strings. These methods directly interpolate user-supplied values without stripping or escaping special characters that serve as directive separators in CSP specifications. When an attacker can influence the :sandbox, :plugin_types, or :report_to parameters through APIs like secure_headers.override_content_security_policy_directives or append methods, they can inject malicious directives by embedding semicolon characters that terminate existing policy statements and introduce new ones.
The operational impact of this vulnerability extends beyond simple XSS exploitation to encompass broader security control bypass mechanisms. An attacker who successfully injects a directive such as script-src 'unsafe-inline' * can effectively neutralize legitimate security policies by placing their malicious directive before the intended policy, thereby enabling cross-site scripting attacks against applications that rely on secure_headers for CSP management. Additionally, the vulnerability enables CSP report exfiltration capabilities where attackers can manipulate report_to directives to redirect security violation reports to attacker-controlled endpoints, potentially exposing application security configurations and attack surfaces.
This vulnerability aligns with CWE-113 - Improper Neutralization of Special Elements in Output Used by a Downstream Component and maps to ATT&CK technique T1059.001 - Command and Scripting Interpreter: PowerShell for the lateral movement aspects of exploiting these insecure header configurations. The issue represents a classic example of insecure input handling in security-critical components where the sanitization process fails to account for the context in which interpolated values will be used within structured policy strings. Organizations deploying applications using vulnerable versions of secure_headers face significant risk of privilege escalation through XSS attacks and information disclosure via CSP violation reporting mechanisms, particularly in environments where user input is not properly validated before being passed to security header configuration APIs.
The fix implemented in version 7.3.0 addresses this vulnerability by introducing proper input sanitization procedures that scrub or escape semicolon, carriage return, and line feed characters from user-supplied values before they are interpolated into CSP directive strings. This remediation ensures that caller-provided data cannot inadvertently break the structural integrity of security policies, thereby preventing the injection of malicious directives that could compromise application security. The updated implementation follows industry best practices for secure coding in security libraries and aligns with OWASP Top Ten recommendations for preventing injection vulnerabilities in web applications. Organizations should immediately upgrade to version 7.3.0 or later to eliminate this attack vector and maintain proper CSP enforcement capabilities across their application security posture.