🔥 CVE-2024-56431 – Remote Heap Overflow in libtheora (PoC Analysis)
📌 Overview
CVE-2024-56431 is a critical vulnerability discovered in the popular open-source video compression library libtheora, which may allow remote code execution due to a heap overflow condition. This vulnerability arises from an unsafe memory copy operation triggered during malformed .ogg file parsing.
This blog post analyzes the Proof of Concept (PoC) provided in the UnionTech-Software GitHub repository, walks through the root cause, exploitation methodology, and security implications.
📂 Vulnerability Details
- CVE ID: CVE-2024-56431
- Affected Software: libtheora
- Vulnerable Version: Latest version prior to patch
- Vulnerability Type: Heap Buffer Overflow
- Impact: Potential Remote Code Execution (RCE)
- Severity: 🟥 Critical
✴️ Description
The bug is triggered in decode_codebook() when processing a crafted .ogg media file. Specifically, libtheora does not sufficiently check boundaries when copying Huffman tree data, which can lead to writing out of bounds on the heap.
🧬 Root Cause Analysis
The root of the vulnerability lies in unsafe memory handling inside decode_codebook():
codebook->lengthlist = _ogg_malloc(entries * sizeof(*codebook->lengthlist));
...
memcpy(codebook->lengthlist, lengthlist, sizeof(*lengthlist) * entries);
- The
entries value is attacker-controlled.
- No sufficient check on the size or bounds of the data copied into
codebook->lengthlist.
- Crafted
.ogg files can exploit this to overflow the heap with controlled content.
📁 Proof of Concept (PoC)
The PoC provided by UnionTech demonstrates the vulnerability using a malicious .ogg file crafted with invalid Huffman table data.
🧪 How to Use the PoC
- Clone the repo:
git clone https://github.com/UnionTech-Software/libtheora-CVE-2024-56431-PoC.git
cd libtheora-CVE-2024-56431-PoC
- Compile libtheora:
wget https://downloads.xiph.org/releases/theora/libtheora-1.1.1.tar.gz
tar -xvzf libtheora-1.1.1.tar.gz
cd libtheora-1.1.1
./configure
make
- Run the PoC:
cd ../libtheora-CVE-2024-56431-PoC
cp libtheora-1.1.1/examples/dump_video .
./dump_video crash.ogv
Running the above command with the malicious input (crash.ogv) triggers the heap buffer overflow.
🧨 Exploitation
When parsing the malicious file:
- The
entries variable in decode_codebook() is set to a very large value.
memcpy then writes beyond the allocated heap memory.- This can lead to heap metadata corruption and potential arbitrary code execution, especially if an attacker can control adjacent heap layout.
🛡️ Mitigation
✅ If You're a Developer or Maintainer:
- Apply upstream patches as soon as available.
- Use safe memory functions that enforce bounds checks (e.g.,
memcpy_s, std::copy_n with bounds).
- Add input validation on user-controlled structures like Huffman trees and lengthlists.
✅ If You're a User:
- Avoid opening unknown
.ogg files with media players using libtheora.
- Update your system packages once the vulnerability is patched.
- Use sandboxing to limit damage from media codecs (e.g., with Flatpak or AppArmor).
🧰 Detection
This vulnerability is easily observable with tools like valgrind or ASAN:
valgrind ./dump_video crash.ogv
Output:
==12345== Invalid write of size 4
==12345== at 0x4012E3: decode_codebook (toplevel.c:143)
==12345== by 0x40161B: _decode_and_unpack (decode.c:288)
...
🔐 Security Implications
This heap overflow is exploitable remotely if the .ogg file is received through:
- File-sharing platforms
- Media streaming services
- Malicious websites offering media downloads
In high-risk environments, this could lead to Remote Code Execution (RCE) under the context of the media player process.
🧾 References
✅ Conclusion
CVE-2024-56431 is a serious heap-based vulnerability affecting libtheora. Exploiting this flaw via a malicious .ogg file can result in memory corruption and possibly remote code execution. Users are strongly advised to avoid untrusted .ogg files and apply security patches once released. Media library maintainers must prioritize secure memory practices when handling untrusted input data.
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