CVE-2024-22920

What it actually does

Heap use-after-free in bufferWriteData allows an attacker-controlled buffer to be accessed after it has been freed, resulting in memory corruption that can lead to arbitrary code execution or denial of service.

Why it matters to the business

Users who process untrusted SWF files on affected systems face risk of full system compromise; the issue has been publicly known for an extended period with working exploits available, increasing the chance of targeted local attacks.

How an attack unfolds

An attacker creates a specially crafted SWF file that triggers the use-after-free when processed by swftools. The victim opens the file locally, causing the vulnerable bufferWriteData function to reuse freed memory and allowing the attacker to control execution flow.

How to fix it

Upgrade swftools packages on Debian 11 systems to the fixed version 5.10.221-1 or later. Remove or restrict execution of the affected swftools binaries until updates are applied.

How to confirm the fix worked

Verify installed swftools version is at or above the fixed release; attempt to process known trigger SWF files in a controlled environment and confirm absence of crashes or memory errors reported by sanitizers.

Typical attack path

1. Craft malicious SWF file that manipulates action compilation buffers
2. Deliver file to target via email, web download, or shared storage
3. Victim opens file using affected swftools binary requiring user interaction
4. bufferWriteData performs use-after-free, corrupting heap state
5. Attacker achieves code execution or crash within the local process context

How to detect it

Review process execution logs and file-access telemetry for invocations of swftools binaries on untrusted SWF inputs; correlate with any subsequent unexpected crashes or memory-corruption indicators in system logs.

What your security team should do

• Prioritize patching all Debian 11 systems running swftools within standard change windows given long public exposure and available exploits
• Restrict swftools usage to trusted file sources only until patches are deployed
• Add swftools binaries to application allow-listing controls where feasible
• Monitor vulnerability disclosure feeds for any increase in EPSS or new exploit code