CVE-2018-16477 in Active Storage
Summary
by MITRE
A bypass vulnerability in Active Storage >= 5.2.0 for Google Cloud Storage and Disk services allow an attacker to modify the `content-disposition` and `content-type` parameters which can be used in with HTML files and have them executed inline. Additionally, if combined with other techniques such as cookie bombing and specially crafted AppCache manifests, an attacker can gain access to private signed URLs within a specific storage path.
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Analysis
by VulDB Data Team • 04/16/2020
The vulnerability identified as CVE-2018-16477 represents a critical security flaw in Rails Active Storage components version 5.2.0 and later, specifically affecting implementations that utilize Google Cloud Storage and local disk services. This issue stems from insufficient validation of user-supplied parameters within the storage system's metadata handling mechanisms, creating an avenue for malicious actors to manipulate file attributes that control how content is served and interpreted by web browsers. The flaw manifests when applications process file uploads and subsequently generate URLs for content delivery, allowing unauthorized modification of essential HTTP headers that govern content rendering behavior.
The technical exploitation of this vulnerability occurs through manipulation of the content-disposition and content-type parameters within Active Storage's metadata handling. When attackers can modify these parameters, they gain the ability to influence how browsers interpret and execute files, particularly HTML content that may be served inline rather than as downloads. This creates a potential for cross-site scripting attacks, as browsers may execute HTML content directly in the context of the victim's session when these headers are improperly set. The vulnerability specifically leverages the fact that certain browsers will interpret inline content differently based on content-type headers, potentially executing embedded javascript or other malicious code when HTML files are displayed in the browser context.
The operational impact of this vulnerability extends beyond simple content manipulation to potentially enable more sophisticated attacks when combined with other techniques. Security researchers have identified that attackers can utilize cookie bombing strategies alongside this vulnerability to establish persistent access to private storage paths. Additionally, when combined with specially crafted AppCache manifests, the vulnerability can facilitate unauthorized access to private signed URLs within specific storage paths. This combination of techniques can result in complete compromise of the storage system's access controls, potentially allowing attackers to view, modify, or delete sensitive files that should remain protected. The vulnerability essentially undermines the fundamental security assumptions of the storage system's access control model.
Mitigation strategies for CVE-2018-16477 should prioritize immediate application updates to versions that address the parameter validation issues within Active Storage. Organizations should implement comprehensive input sanitization for all user-supplied parameters that influence content metadata, particularly focusing on content-disposition and content-type headers. The implementation of strict content-type validation and the enforcement of secure content disposition settings can prevent malicious manipulation of file execution contexts. Additionally, organizations should consider implementing additional security layers such as Content Security Policy headers, proper session management, and monitoring for unusual access patterns to storage resources. This vulnerability aligns with CWE-20 Improper Input Validation and can be mapped to ATT&CK technique T1059 Command and Scripting Interpreter when combined with XSS payloads, representing a significant risk to web application security and data integrity.