CVE-2016-4348 in librsvg
Summary
by MITRE
The _rsvg_css_normalize_font_size function in librsvg 2.40.2 allows context-dependent attackers to cause a denial of service (stack consumption and application crash) via circular definitions in an SVG document.
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Analysis
by VulDB Data Team • 08/21/2022
The vulnerability identified as CVE-2016-4348 resides within the librsvg library version 2.40.2, specifically within the _rsvg_css_normalize_font_size function. This flaw represents a classic stack-based buffer overflow condition that can be exploited through carefully crafted SVG documents containing circular definitions. The issue manifests when the library processes font size normalization logic, creating a recursive evaluation scenario that consumes excessive stack memory. Such vulnerabilities fall under the category of CWE-772, which describes missing release of resource after effective lifetime, and more specifically align with CWE-121, stack-based buffer overflow, when considering the exploitation mechanism. The vulnerability demonstrates a fundamental flaw in input validation and recursive processing logic within the SVG rendering pipeline.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enabling more sophisticated attack vectors. When an attacker crafts an SVG document with circular font size definitions, the _rsvg_css_normalize_font_size function enters an infinite recursion loop that rapidly consumes stack space until the application crashes or becomes unresponsive. This behavior creates a predictable denial of service condition that can be exploited by any application or service that processes SVG files through the affected librsvg library. The attack requires no special privileges and can be executed through normal file processing workflows, making it particularly dangerous in web applications, email clients, or content management systems that handle user-uploaded SVG content. The vulnerability aligns with ATT&CK technique T1499.004, which covers network denial of service attacks, and demonstrates how seemingly benign file format processing can become a vector for system instability.
Mitigation strategies for CVE-2016-4348 should focus on immediate library updates to versions that have patched the recursive evaluation flaw. Organizations must ensure all systems processing SVG content have librsvg updated to version 2.40.3 or later, which contains the necessary fixes for the circular reference handling. Additionally, implementing input validation measures that detect and reject SVG documents with excessive nesting or circular references provides an additional defensive layer. System administrators should consider deploying application firewalls or content filtering solutions that can identify suspicious SVG patterns before they reach vulnerable applications. The vulnerability highlights the importance of proper resource management in recursive algorithms and serves as a reminder that even standard file format parsers can contain dangerous recursion patterns. Security monitoring should include detection of unusual stack consumption patterns and application crashes related to SVG processing, as these may indicate exploitation attempts. Organizations should also review their SVG handling workflows to ensure proper sandboxing and resource limiting mechanisms are in place to prevent similar issues in other components of their application stack.