CVE-2018-16831 in Smarty
Summary
by MITRE
Smarty before 3.1.33-dev-4 allows attackers to bypass the trusted_dir protection mechanism via a file:./../ substring in an include statement.
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Analysis
by VulDB Data Team • 05/08/2023
The vulnerability identified as CVE-2018-16831 affects the Smarty template engine version 3.1.33-dev-4 and earlier, representing a critical security flaw that undermines the intended protection mechanisms within the software. This issue specifically targets the trusted directory validation system that Smarty implements to prevent unauthorized file access through template includes. The flaw enables malicious actors to circumvent security controls by exploiting a particular pattern in file path references that should normally be restricted.
The technical implementation of this vulnerability stems from insufficient input validation within Smarty's include statement processing logic. When an attacker crafts a malicious include directive containing the file:./../ substring, the template engine fails to properly sanitize or validate the path components, allowing arbitrary file access beyond the designated trusted directories. This bypass mechanism operates by manipulating the relative path traversal logic that should normally restrict file access to predefined safe locations. The vulnerability essentially allows attackers to traverse directory structures and access files that should be protected by the trusted directory configuration.
The operational impact of this vulnerability is severe and multifaceted, potentially enabling attackers to access sensitive system files, configuration data, and other protected resources. An attacker could leverage this flaw to read arbitrary files on the server, potentially extracting database credentials, application secrets, or other confidential information. The vulnerability also opens possibilities for remote code execution if combined with other attack vectors, as it provides a method for accessing files that might contain executable code or configuration elements that could be manipulated. This makes the vulnerability particularly dangerous in web application environments where Smarty is used for template processing.
The security implications extend beyond simple file access, as this vulnerability aligns with common attack patterns documented in the ATT&CK framework under privilege escalation and credential access tactics. The CWE classification for this issue would likely fall under CWE-22 - Improper Limitation of a Pathname to a Restricted Directory, which specifically addresses path traversal vulnerabilities that allow attackers to access files outside of intended directories. Organizations using Smarty templates without proper updates face significant risk of data breaches and system compromise, particularly in environments where template processing handles user-supplied input.
Mitigation strategies should focus on immediate patching of Smarty to version 3.1.33-dev-4 or later, which contains the necessary fixes for this vulnerability. Additionally, administrators should implement proper input validation for all template include statements and consider restricting template processing capabilities to minimize the impact of potential exploitation. Network-level protections such as web application firewalls can provide additional defense-in-depth measures, while regular security assessments should verify that no other similar vulnerabilities exist in the template processing pipeline. Organizations should also review their trusted directory configurations and ensure that proper access controls are in place to limit the potential damage from any successful exploitation attempts.