CVE-2021-39582

What it actually does

Heap buffer overflow in swf_GetPlaceObject within swfobject.c allows out-of-bounds write and subsequent arbitrary code execution when processing a crafted SWF file.

Why it matters to the business

Attackers can gain full control of systems that use this unmaintained tool to inspect or convert SWF files, leading to potential data theft, ransomware deployment, or lateral movement; the project has released no patches since 2020 and remains widely present in legacy media workflows.

How an attack unfolds

An attacker creates a malicious SWF file that triggers the overflow when parsed by swf_GetPlaceObject. The victim opens the file using any swftools utility; the overflow overwrites heap memory to redirect execution to attacker-controlled code, achieving local code execution on the victim's machine.

How to fix it

Immediately replace swftools with a maintained alternative for SWF processing; if continued use is unavoidable, compile from source with hardened memory allocators and strict sandboxing, or remove the affected binary from all systems.

How to confirm the fix worked

Confirm the installed swftools version is newer than 20200710 or that the binary has been rebuilt with the upstream buffer-size checks; test by feeding known-good and known-malicious SWF samples and verifying absence of crashes or unexpected exits.

Typical attack path

1. Craft a specially malformed SWF file that overflows the heap buffer in swf_GetPlaceObject
2. Deliver the file via email, download link, or shared storage to a target user or automated processing pipeline
3. Victim or script invokes an swftools binary on the file
4. Overflow occurs, shellcode or ROP chain executes, establishing attacker control

How to detect it

Search process-creation and file-access logs for invocations of swftools utilities on externally sourced SWF files; monitor for segmentation faults or heap-related crashes in those processes.

What your security team should do

• Inventory all systems and build pipelines that still ship or invoke swftools and schedule removal within 30 days
• Block execution of swftools binaries via application allow-listing until replacement is complete
• Add SWF file ingestion to the list of high-risk file types monitored by EDR and sandbox solutions