CVE-2018-7731 in Exempi
Summary
by MITRE
An issue was discovered in Exempi through 2.4.4. XMPFiles/source/FormatSupport/WEBP_Support.cpp does not check whether a bitstream has a NULL value, leading to a NULL pointer dereference in the WEBP::VP8XChunk class.
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Analysis
by VulDB Data Team • 02/17/2023
The vulnerability identified as CVE-2018-7731 represents a critical null pointer dereference flaw within the Exempi library version 2.4.4 and earlier. This issue specifically resides in the XMPFiles component's WEBP_Support.cpp file where the software fails to validate bitstream data for null values before attempting to process them. The flaw occurs within the WEBP::VP8XChunk class which handles WebP image format metadata processing, making it particularly dangerous in environments where Exempi is used for handling multimedia content. The absence of proper input validation creates a scenario where maliciously crafted WebP files can trigger the vulnerability during metadata extraction or processing operations.
The technical implementation of this vulnerability stems from inadequate null pointer checks in the bitstream processing pipeline. When the WEBP_Support.cpp module encounters a WebP file with malformed or incomplete bitstream data, it attempts to dereference a null pointer without first verifying that the pointer contains valid data. This fundamental flaw violates secure coding practices and creates a direct pathway for denial of service conditions. The vulnerability manifests as a crash during the processing of WebP metadata, which can be exploited by attackers to cause application instability or complete system crashes. From a cybersecurity perspective, this represents a classic example of a null pointer dereference that can be leveraged for service disruption attacks.
The operational impact of CVE-2018-7731 extends beyond simple application crashes to encompass broader security implications within content processing systems. Systems that rely on Exempi for handling multimedia files, particularly those in digital asset management, content delivery networks, or media processing pipelines, become vulnerable to denial of service attacks. Attackers can craft malicious WebP files that trigger the null pointer dereference, causing legitimate applications to crash and potentially rendering services unavailable. This vulnerability is particularly concerning in automated processing environments where batch operations are common, as a single malicious file could cause cascading failures across multiple processing tasks. The flaw aligns with CWE-476 which specifically addresses null pointer dereference conditions, and can be mapped to ATT&CK technique T1499.1 for network denial of service attacks.
Mitigation strategies for this vulnerability require immediate patching of the Exempi library to version 2.4.5 or later where the null pointer checks have been implemented. Organizations should also implement input validation measures at the application level, including file type verification and size restrictions for WebP content before processing. Network-based defenses can include content filtering rules that block suspicious WebP files or implement sandboxing techniques to isolate potentially malicious content. Security teams should monitor for exploitation attempts and consider implementing automated patch management processes to ensure all systems using Exempi are protected against this vulnerability. The fix implemented in the patched version addresses the root cause by adding proper null checks in the WEBP_Support.cpp module, specifically within the WEBP::VP8XChunk class processing logic.