CVE-2021-39575

What it actually does

NULL pointer dereference in dump_method() within abc.c crashes the swftools process when parsing a crafted SWF file.

Why it matters to the business

Attackers can cause application crashes that interrupt any workflows or scripts relying on swftools for SWF file handling, leading to operational downtime.

How an attack unfolds

An attacker supplies a malicious SWF file that reaches the vulnerable dump_method function during normal file processing, triggering the dereference and immediate crash.

How to fix it

No fixed versions are published; discontinue use of swftools on untrusted inputs or replace it with an unaffected alternative.

How to confirm the fix worked

Attempt to process known crashing SWF samples with the updated binary and confirm the process no longer terminates unexpectedly.

Typical attack path

1. Create a specially crafted SWF file that triggers the NULL dereference
2. Deliver the file to a target system via email, download, or shared storage
3. Victim opens or processes the file using an affected swftools binary
4. Application terminates with a segmentation fault or crash

How to detect it

Monitor process logs and crash dumps for segmentation faults or abrupt exits immediately after swftools opens an SWF file.

What your security team should do

• Block or sandbox untrusted SWF files before any swftools processing
• Replace swftools with a maintained alternative in all production pipelines
• Add crash monitoring for swftools binaries in security logging