CVE-2019-18856 in SVG Sanitizer Module
Summary
by MITRE
A Denial Of Service vulnerability exists in the SVG Sanitizer module through 8.x-1.0-alpha1 for Drupal because access to external resources with an SVG use element is mishandled.
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Analysis
by VulDB Data Team • 02/11/2024
The vulnerability identified as CVE-2019-18856 represents a critical denial of service weakness within the SVG Sanitizer module for Drupal platforms. This issue affects versions through 8.x-1.0-alpha1 and stems from improper handling of external resource access when processing SVG use elements. The security flaw arises from the module's inadequate validation and sanitization mechanisms that fail to properly restrict access to external resources referenced within SVG markup. When Drupal processes SVG files containing use elements that reference external resources, the sanitizer module does not adequately prevent malicious actors from exploiting this functionality to consume excessive system resources or cause application instability.
The technical implementation of this vulnerability occurs through the manipulation of SVG use elements that can reference external resources via xlink:href attributes. When the sanitizer processes such elements, it fails to properly validate or restrict the external resource access, allowing attackers to craft malicious SVG files that can trigger resource exhaustion or infinite loops. This weakness directly maps to CWE-400, which categorizes excessive resource consumption as a fundamental security issue. The vulnerability enables attackers to construct SVG files that, when processed by the sanitizer, can cause the web server to consume excessive CPU cycles or memory resources, ultimately leading to service disruption. The flaw essentially allows an attacker to craft SVG content that can cause the application to enter a state of resource exhaustion or operational failure.
From an operational perspective, this vulnerability significantly impacts Drupal installations that utilize the SVG Sanitizer module for processing user-uploaded or content management system generated SVG graphics. The denial of service condition can manifest as complete application unavailability, slow response times, or resource exhaustion that affects other services running on the same infrastructure. Attackers can exploit this weakness by uploading malicious SVG files containing use elements that reference external resources, causing the sanitizer to attempt to access these resources and potentially trigger resource exhaustion. The impact extends beyond simple service disruption as it can affect the entire hosting environment, particularly in multi-tenant scenarios where one compromised application could affect others. This vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks through resource exhaustion.
The recommended mitigation strategies include immediate upgrading to patched versions of the SVG Sanitizer module where available, implementing additional input validation for SVG content, and configuring proper resource limits for web server processes. Administrators should also consider implementing content filtering mechanisms that restrict the use of external resource references within SVG elements. The module should be configured to either disable external resource access entirely or implement strict whitelisting of allowed external resources. Additionally, organizations should deploy monitoring solutions to detect unusual resource consumption patterns that may indicate exploitation attempts. The vulnerability underscores the importance of proper input sanitization and resource management in web applications, particularly those handling rich media content like SVG graphics. Security teams should also consider implementing automated scanning tools that can detect potentially malicious SVG content before it can be processed by the sanitizer module.