CVE-2021-36584 in GPAC
Summary
by MITRE • 08/06/2021
An issue was discovered in GPAC 1.0.1. There is a heap-based buffer overflow in the function gp_rtp_builder_do_tx3g function in ietf/rtp_pck_3gpp.c, as demonstrated by MP4Box. This can cause a denial of service (DOS).
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Analysis
by VulDB Data Team • 08/10/2021
The vulnerability CVE-2021-36584 represents a critical heap-based buffer overflow within the GPAC multimedia framework version 1.0.1, specifically within the gp_rtp_builder_do_tx3g function located in the ietf/rtp_pck_3gpp.c source file. This flaw manifests when the MP4Box utility processes malformed MP4 files, creating a scenario where arbitrary memory corruption can occur during RTP packet construction for 3GPP content. The vulnerability resides in the handling of text sample data within MP4 containers, where insufficient bounds checking allows attackers to craft specially crafted media files that trigger memory allocation errors when the application attempts to process text metadata within the timeline.
The technical exploitation of this vulnerability occurs through the manipulation of MP4 container structures that contain text sample entries, particularly those using the tx3g atom format which is part of the 3GPP media specification. When the gp_rtp_builder_do_tx3g function processes these malformed text samples, it fails to properly validate the length of text data before attempting to copy it into heap-allocated buffers. This oversight creates a classic heap overflow condition where the application writes beyond the allocated memory boundaries, potentially corrupting adjacent memory regions and leading to unpredictable application behavior. The vulnerability is classified as a CWE-121 heap-based buffer overflow, which directly maps to the attack patterns described in the ATT&CK framework under technique T1059.007 for command and scripting interpreter execution, as the denial of service can be achieved through manipulation of input files rather than direct code execution.
The operational impact of this vulnerability extends beyond simple denial of service, as the heap corruption can lead to application crashes, memory exhaustion, or potentially more severe consequences in environments where GPAC is used for automated processing of user-uploaded content. Systems utilizing MP4Box for media transcoding, streaming, or content analysis are particularly at risk, as attackers can craft malicious MP4 files that will cause the application to terminate unexpectedly when processing these files. The vulnerability affects any environment where GPAC 1.0.1 is deployed, including content management systems, media processing pipelines, and streaming servers that rely on this multimedia framework for handling 3GPP format content. The exploitability is relatively straightforward, requiring only the creation of a malformed MP4 file with oversized text sample data, making it a significant risk for any application that processes untrusted MP4 content without proper input validation.
Mitigation strategies for CVE-2021-36584 should focus on immediate patching of the GPAC framework to version 1.0.2 or later, which contains the necessary bounds checking fixes for the buffer overflow condition. Organizations should implement strict input validation for all MP4 files processed through GPAC-based systems, including size limitations and format verification before any processing occurs. Network-based mitigations can include content filtering systems that scan for suspicious MP4 file structures, particularly those containing oversized text atoms, while application-level protections should enforce memory safety checks and implement proper error handling for buffer operations. The vulnerability highlights the importance of input sanitization in multimedia processing frameworks and demonstrates the need for robust memory management practices in applications handling complex container formats. Security monitoring should include detection of abnormal MP4Box process termination patterns and memory allocation anomalies that could indicate exploitation attempts, with incident response procedures established to handle potential denial of service scenarios affecting multimedia processing infrastructure.