CVE-2016-6163 in librsvg2
Summary
by MITRE
The rsvg_pattern_fix_fallback function in rsvg-paint_server.c in librsvg2 2.40.2 allows remote attackers to cause a denial of service (out-of-bounds read) via a crafted svg file.
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Analysis
by VulDB Data Team • 08/10/2020
The vulnerability identified as CVE-2016-6163 resides within the librsvg2 library version 2.40.2, specifically in the rsvg_pattern_fix_fallback function located in the rsvg-paint_server.c source file. This flaw represents a critical security issue that enables remote attackers to execute denial of service attacks through carefully crafted svg files. The vulnerability manifests as an out-of-bounds read condition that occurs when the library processes malformed pattern elements within svg graphics, fundamentally compromising the stability and reliability of applications that rely on librsvg2 for svg rendering operations. The issue stems from inadequate input validation and memory access controls within the pattern fallback handling mechanism, creating a scenario where maliciously constructed svg content can trigger unexpected memory access patterns.
The technical exploitation of this vulnerability occurs when an attacker crafts an svg file containing malformed pattern definitions that, when processed by librsvg2, cause the rsvg_pattern_fix_fallback function to attempt reading memory locations beyond the allocated bounds of the pattern data structures. This out-of-bounds read condition can lead to unpredictable application behavior, including crashes, memory corruption, or system instability. The vulnerability is particularly concerning because it can be triggered through normal svg rendering operations without requiring any special privileges or user interaction beyond viewing the malicious content. The flaw operates at the core rendering engine level, making it difficult to isolate and prevent through traditional application-level security measures.
From an operational perspective, this vulnerability poses significant risks to web applications, desktop environments, and any systems that process untrusted svg content. The denial of service impact can be severe as it can cause complete application crashes, rendering systems unusable until restart or manual intervention. Security researchers have classified this issue under CWE-125 as an out-of-bounds read vulnerability, which aligns with the observed behavior of accessing memory beyond allocated buffers. The attack surface is extensive since svg files are commonly used in web browsers, email clients, graphic design applications, and document viewers. Organizations using librsvg2 in production environments face potential disruptions to their services, as even a single malicious svg file can bring down entire applications or systems.
The mitigation strategies for CVE-2016-6163 primarily involve immediate patching of affected librsvg2 installations to version 2.40.3 or later, which contains the necessary code fixes to properly validate pattern data and prevent out-of-bounds memory access. Additionally, organizations should implement input sanitization measures that validate svg content before processing, particularly when handling untrusted user uploads or external content. Network-level protections can include svg content filtering and sandboxing mechanisms that isolate svg processing to prevent cascading failures. Security teams should also consider implementing monitoring for unusual application crashes or memory access patterns that could indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under the T1499.004 sub-technique for Network Denial of Service, as it represents a method for causing service unavailability through malformed input processing. System administrators should also ensure that all applications using librsvg2 are regularly updated and that proper security monitoring is in place to detect potential exploitation attempts.