CVE-2024-56431

What it actually does

Invalid negative left shift in oc_huff_tree_unpack during Huffman tree unpacking in libtheora, resulting in undefined behavior that may cause crashes or memory corruption when processing malformed Theora bitstreams.

Why it matters to the business

Potential service disruption or application crashes when handling untrusted Theora media on legacy Ubuntu systems; low prevalence and exploit maturity reduce immediate operational risk but require patching to avoid future exposure in media pipelines.

How an attack unfolds

An attacker supplies a crafted Theora-encoded file or stream containing invalid Huffman tree data that reaches oc_huff_tree_unpack and triggers the negative shift, leading to undefined behavior exploitable for denial of service or potentially arbitrary code execution.

How to fix it

Upgrade affected packages to the listed fixed versions: linux-aws (14.04) to 4.4.0-1002.2, linux-lts-xenial (14.04) to 4.4.0-24.43~14.04.1, linux (16.04) to 4.4.0-24.43, linux-aws (16.04) to 4.4.0-1001.10, linux-gke (16.04) to 4.4.0-1003.3, linux-hwe (16.04) to 4.8.0-36.36~16.04.1, linux-raspi2 (16.04) to 4.4.0-1012.16, linux-snapdragon (16.04) to 4.4.0-1015.18.

How to confirm the fix worked

Confirm package versions match or exceed the fixed releases above; test media decoding paths with known-good and boundary-case Theora streams to verify absence of shift errors.

Typical attack path

1. Identify target applications or services that use libtheora for decoding Theora content
2. Craft a malicious Theora bitstream with invalid Huffman tree parameters
3. Deliver the payload via file upload, media streaming, or network input
4. Trigger processing to induce the negative left shift and resulting undefined behavior

How to detect it

Review application logs for segmentation faults or undefined behavior during Theora decoding; inspect media processing pipelines for unexpected crashes on untrusted input.

What your security team should do

• Prioritize upgrades on any remaining Ubuntu 14.04/16.04 systems still using the affected kernels
• Remove or isolate legacy Theora decoding dependencies where possible
• Monitor EPSS and KEV updates for any rise in exploit activity