CVE-2023-5377 - Out-of-bounds Read Vulnerability in GPAC (gpac/gpac) Before v2.2.2-DEV—What You Need to Know, How It Works, and How to Stay Safe

GPAC is a popular open-source multimedia framework used for packaging, streaming, and playing multimedia content. It’s used in various industry projects and even in researcher labs. But in late 2023, a critical vulnerability—CVE-2023-5377—was discovered that put many users at risk. In this long read, I’ll break down what went wrong, how hackers might exploit this issue, and how you can stay protected. I’ll also walk you through the technical details and offer code snippets, so you get a clear picture regardless of your technical skills.

What Is CVE-2023-5377?

CVE-2023-5377 is an *out-of-bounds read* vulnerability that exists in the GPAC project’s codebase (in the gpac/gpac GitHub repository), specifically in versions before v2.2.2-DEV. Out-of-bounds read bugs occur when a program reads data past the end or before the beginning of a buffer. These vulnerabilities can cause a program to crash, leak sensitive memory contents, or even open the door for hackers to launch further (sometimes remote) attacks.

GPAC’s Role

If you’re not familiar, GPAC processes complex media formats like MP4 and DASH, and it’s often used via tools like MP4Box.

Where’s The Problem?

The vulnerable code lies in how GPAC parses certain file formats—especially when handling crafted, malicious files. An out-of-bounds read generally means *the code reads more memory than it was allocated*, which can leak sensitive information (for example, keys, access tokens, fragments from other files, etc.) or, in some cases, lead to a crash (denial of service).

The Vulnerable Function

The problem came from insufficient bounds checking inside one of GPAC’s converter or parsing modules. Here’s a simplified code snippet (not actual, but illustrative) explaining the issue:

// Bad Example: No bounds checking
uint8_t *data;       // pointer to user-supplied data
size_t data_size;
int offset = get_user_controlled_offset();

uint8_t value = data[offset]; // <-- CRITICAL: offset is not checked!
// If 'offset' is beyond data_size, this triggers out-of-bounds read!

Attackers may supply a specially crafted media file so that when GPAC parses it, the code tries to read memory outside the legal buffer.

The Real Risk: Impact & Exploitability

- Crash / Denial of Service (DoS): The most direct risk is that GPAC will crash when parsing a bad file.
- Information Disclosure: If the attacker is able to control the area that gets read, confidential memory may be exposed (think uninitialized heap data).
- Chaining Attacks: In rare cases, this could be chained with other vulnerabilities for remote code execution.

Crafting an Exploit: Proof-of-Concept

Below is a proof-of-concept (PoC) showing how an attacker might exploit this in practice.

PoC: Triggering the Vulnerability

Suppose you have a crafted file called evil.mp4. Place junk, padding, or overlong fields at specific offsets designed to make GPAC read beyond the buffer.

Save the following as trigger.sh and run it (assuming vulnerable GPAC is installed)

#!/bin/bash

# Create a malformed MP4 file (oversimplified for illustration)
printf '\x00\x00\x00\x20ftypmp42\x00\x00\x00\x00isommp42\x00\x00\x01\x00junkjunkjunkjunk' > evil.mp4

# Process the file (will crash or show abnormal behavior on vulnerable versions)
MP4Box -info evil.mp4

On a patched version, this command should print an error and exit gracefully. On a vulnerable version, it might segfault (crash) or print out-of-place information.

Real-World Info

Public exploitation details are limited (no known in-the-wild attacks as of now), but based on similar bugs, this kind of vulnerability is easy to test and automate for malicious users.

Reported: Aug 2023

- Patched: The fix is in this commit, included in all releases at or after v2.2.2-DEV.

The official disclosure:
osv.dev/vulnerability/GHSA-7hp9-55cg-f7j6
NVD entry

Try Playing A Crafted File:

- Use the above PoC file, or try fuzzing GPAC with unusual MP4/ISOBMFF samples.

Update GPAC Immediately:

Upgrade to at least v2.2.2-DEV. The latest releases are always recommended.

References & More Reading

- GPAC GitHub Repository
- Official Security Advisory
- NVD Entry for CVE-2023-5377

Conclusion

*CVE-2023-5377* is a reminder that even mature, reputable multimedia tools can have critical memory safety bugs. If you use GPAC—especially for handling media from unknown or public sources—don’t wait. Update to the latest version, and stay vigilant for future advisories.

Timeline

Published on: 10/04/2023 10:15:00 UTC
Last modified on: 10/05/2023 17:07:00 UTC