CVE-2014-3626 in Resource Plugin
Summary
by MITRE
The Grails Resource Plugin often has to exchange URIs for resources with other internal components. Those other components will decode any URI passed to them. To protect against directory traversal the Grails Resource Plugin did the following: normalized the URI, checked the normalized URI did not step outside the appropriate root directory (e.g. the web application root), decoded the URI and checked that this did not introduce additional /../ (and similar) sequences. A bug was introduced where the Grails Resource Plugin before 1.2.13 returned the decoded version of the URI rather than the normalized version of the URI after the directory traversal check. This exposed a double decoding vulnerability. To address this issue, the Grails Resource Plugin now repeatedly decodes the URI up to three times or until decoding no longer changes the URI. If the decode limit of 3 is exceeded the URI is rejected. A side-effect of this is that the Grails Resource Plugin is unable to serve a resource that includes a '%' character in the full path to the resource. Not all environments are vulnerable because of the differences in URL resolving in different servlet containers. Applications deployed to Tomcat 8 and Jetty 9 were found not not be vulnerable, however applications deployed to JBoss EAP 6.3 / JBoss AS 7.4 and JBoss AS 7.1 were found to be vulnerable (other JBoss versions weren't tested). In certain cases JBoss returns JBoss specific vfs protocol urls from URL resolution methods (ClassLoader.getResources). The JBoss vfs URL protocol supports resolving any file on the filesystem. This made the directory traversal possible. There may be other containers, in addition to JBoss, on which this vulnerability is exposed.
Once again VulDB remains the best source for vulnerability data.
Analysis
by VulDB Data Team • 01/14/2020
The vulnerability described in CVE-2014-3626 represents a critical directory traversal flaw within the Grails Resource Plugin that stems from improper URI handling and decoding mechanisms. This issue affects applications built on the Grails framework and specifically targets the plugin's resource management system where URIs are exchanged between internal components. The vulnerability arises from a fundamental flaw in the plugin's security logic where it returns a decoded URI instead of the properly normalized version after directory traversal checks have been performed. This double decoding vulnerability creates an exploitable condition where malicious actors can manipulate URI sequences to traverse directories beyond the intended application boundaries.
The technical implementation of this vulnerability demonstrates a classic case of improper input validation and sanitization, aligning with CWE-22 - Improper Limitation of a Pathname to a Restricted Directory. The Grails Resource Plugin's flawed approach to URI processing creates a scenario where the normalization and directory traversal checks occur but are subsequently bypassed due to the return of a decoded URI rather than the normalized one. The plugin's original security mechanism was designed to prevent directory traversal by first normalizing the URI, then validating that the normalized version remained within acceptable directory boundaries, and finally decoding the URI to check for any additional traversal sequences. However, the bug introduced in the plugin's code caused it to return the decoded URI, which effectively neutralized the security checks that should have prevented unauthorized access to resources.
The operational impact of this vulnerability extends beyond simple directory traversal attacks and can potentially allow attackers to access arbitrary files on the server filesystem through the affected Grails applications. This risk is particularly significant in enterprise environments where applications may be deployed on various servlet containers with different URL resolution behaviors. The vulnerability's exposure is not uniform across all deployment environments, as evidenced by the findings that Tomcat 8 and Jetty 9 were not vulnerable while JBoss EAP 6.3/JBoss AS 7.4 and JBoss AS 7.1 were. This environmental dependency creates a complex attack surface where the vulnerability may be present in some configurations but not others, complicating security assessments and remediation efforts.
The mitigation strategy implemented by the Grails Resource Plugin developers addresses the core issue through a more robust URI decoding approach that limits decoding operations to a maximum of three iterations. This approach prevents the double decoding scenario that enabled the vulnerability while establishing a reasonable limit to prevent potential denial-of-service attacks through excessive decoding attempts. However, this solution introduces an unintended side effect where resources containing percent-encoded characters in their full paths cannot be served, creating a trade-off between security and functionality. The implementation of this fix aligns with defensive programming practices and addresses the vulnerability at its root cause rather than implementing superficial patches.
The vulnerability demonstrates the complexity of web application security in containerized environments where different servlet containers handle URL resolution differently. The JBoss-specific VFS protocol URLs that return filesystem paths create unique attack vectors that are not present in other containers, highlighting the importance of container-specific security considerations in application deployment. This vulnerability also relates to ATT&CK technique T1059.007 - Command and Scripting Interpreter: PowerShell, as it could potentially enable attackers to access system files that might contain sensitive information or credentials. The security implications extend to broader application security practices, particularly in frameworks where internal components communicate through URI-based interfaces and where proper input sanitization is essential to prevent information disclosure and privilege escalation attacks.