CVE-2021-35306 in Bento4
Summary
by MITRE • 08/06/2021
An issue was discovered in Bento4 through v1.6.0-636. A NULL pointer dereference exists in the function AP4_StszAtom::WriteFields located in Ap4StszAtom.cpp. It allows an attacker to cause a denial of service (DOS).
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Analysis
by VulDB Data Team • 08/10/2021
The vulnerability CVE-2021-35306 represents a critical null pointer dereference flaw within the Bento4 multimedia framework version 1.6.0-636 and earlier. This issue resides in the AP4_StszAtom::WriteFields function located in the Ap4StszAtom.cpp source file, making it a fundamental component of the MP4 container processing pipeline. The flaw manifests when the application attempts to write fields to a stsz atom without proper validation of pointer references, creating an exploitable condition that can be triggered through malformed input files. The Bento4 library is widely used for MP4 file manipulation and streaming applications, making this vulnerability particularly concerning for media processing systems. The vulnerability falls under CWE-476 which specifically addresses NULL pointer dereference conditions, representing a classic software error pattern that has been documented in security literature for decades. This type of vulnerability typically occurs when developers assume that certain pointers will always contain valid addresses without proper null checking mechanisms. The impact of this vulnerability extends beyond simple denial of service as it can be leveraged by attackers to disrupt legitimate service operations through carefully crafted malicious media files.
The technical exploitation of this vulnerability requires an attacker to craft a specially formatted MP4 file containing malformed stsz atoms that will trigger the null pointer dereference during the WriteFields operation. When the AP4_StszAtom::WriteFields function executes, it attempts to access memory locations through pointers that have not been properly initialized or validated, leading to an immediate system crash or termination of the affected process. This behavior aligns with the ATT&CK technique T1499.004 which describes network denial of service attacks through resource exhaustion or process termination. The vulnerability is particularly dangerous in automated processing environments where media files are ingested without proper validation, as a single malicious file can bring down entire media processing pipelines. The null pointer dereference occurs during the write operation of the sample size atom, which is a fundamental structure in MP4 containers used to store sample size information for audio and video streams. This makes the attack surface particularly broad as any application using Bento4 for MP4 file processing could be affected, including content delivery networks, media servers, and streaming platforms.
The operational impact of CVE-2021-35306 extends far beyond simple system crashes, creating significant risks for organizations that rely on Bento4 for media processing workflows. When exploited, this vulnerability can cause denial of service conditions that disrupt legitimate user access and business operations, potentially leading to revenue loss for streaming services and content providers. The vulnerability affects systems that process MP4 files through Bento4, which includes but is not limited to video encoding platforms, content management systems, and media delivery infrastructure. Organizations using vulnerable versions of Bento4 should consider this vulnerability as a critical threat to their operational continuity, particularly in environments where automated media processing occurs. The attack vector is relatively simple and does not require sophisticated techniques, making it accessible to a broad range of threat actors from script kiddies to organized cybercriminals. This vulnerability demonstrates the importance of proper input validation and defensive programming practices, as the fix typically involves adding null pointer checks before accessing any pointer-based memory locations. The severity classification of this vulnerability should be considered high due to its potential for denial of service and the wide deployment of Bento4 across various media processing applications. Security teams should prioritize patching this vulnerability in their environments to prevent potential exploitation that could result in service disruption and business impact. The remediation approach involves updating to a patched version of Bento4 where the null pointer dereference has been eliminated through proper validation of pointer references before memory access operations.