CVE-2025-27111 in Rack
Summary
by MITRE • 03/04/2025
Rack is a modular Ruby web server interface. The Rack::Sendfile middleware logs unsanitised header values from the X-Sendfile-Type header. An attacker can exploit this by injecting escape sequences (such as newline characters) into the header, resulting in log injection. This vulnerability is fixed in 2.2.12, 3.0.13, and 3.1.11.
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Analysis
by VulDB Data Team • 10/10/2025
The vulnerability identified as CVE-2025-27111 affects Rack, a fundamental Ruby web server interface that serves as a modular framework for building web applications. This middleware component specifically processes file delivery operations through the Rack::Sendfile functionality, which enables applications to efficiently serve static files by delegating the task to the web server. The issue stems from inadequate input sanitization within the logging mechanism that processes the X-Sendfile-Type header, creating a pathway for malicious actors to manipulate log outputs through carefully crafted header values.
The technical flaw manifests when the Rack::Sendfile middleware logs header values without proper sanitization of special characters, particularly newline sequences and other control characters. Attackers can exploit this weakness by injecting escape sequences into the X-Sendfile-Type header, which then get processed and logged without proper filtering. This log injection vulnerability allows malicious actors to manipulate log files by introducing newlines or other special characters that can break log parsing mechanisms, potentially leading to log forging attacks where attackers can inject false entries into log files. The vulnerability affects multiple versions of the Rack framework, with patches available in versions 2.2.12, 3.0.13, and 3.1.11, representing the specific releases that address this security gap.
The operational impact of this vulnerability extends beyond simple log manipulation, as it can compromise the integrity of security monitoring systems that rely on properly formatted log entries. When attackers successfully inject escape sequences into log files, they can potentially obscure legitimate activities, create false security alerts, or even manipulate log analysis tools that expect specific formatting patterns. This vulnerability aligns with CWE-117, which describes improper output neutralization for logs, and can be categorized under the ATT&CK technique T1562.006 for "Impair Command History Logging" when leveraged in conjunction with other attack vectors. The vulnerability is particularly concerning in environments where comprehensive logging is critical for security operations, as it can undermine the reliability of audit trails and incident response capabilities.
Organizations utilizing Rack-based applications should prioritize immediate patching of affected versions to mitigate this vulnerability, as the log injection capability provides attackers with a method to manipulate system monitoring and forensic analysis. The fix implemented in the patched versions involves proper sanitization of header values before logging, ensuring that special characters are either escaped or removed from the logging process. Security teams should also implement monitoring for unusual log patterns that might indicate exploitation attempts, while considering additional logging controls to detect and prevent similar vulnerabilities in other components of the application stack. This vulnerability demonstrates the critical importance of input validation in logging systems, particularly in middleware components that process untrusted data from external sources, as it can serve as a stepping stone for more sophisticated attacks that rely on manipulating system audit trails for persistence or evasion purposes.