CVE-2021-39579

What it actually does

Heap buffer overflow in string_hash() allows memory corruption that can lead to arbitrary code execution.

Why it matters to the business

Attackers can gain full control of systems that process untrusted files with the vulnerable tool, risking data theft or ransomware deployment on older unpatched installations.

How an attack unfolds

An attacker supplies a specially crafted input file that triggers the overflow inside string_hash when the tool parses it; public exploit code exists that achieves code execution on vulnerable versions.

How to fix it

No official fixed versions are published; remove swftools from production use, replace with maintained alternatives, or apply source-level patches that eliminate the overflow in q.c.

How to confirm the fix worked

Verify that swftools is no longer present or that custom builds contain bounds checks around string operations in q.c; re-test with known trigger files to confirm absence of crashes or unexpected execution.

Typical attack path

1. Obtain or generate a malicious file that overflows the buffer in string_hash
2. Deliver the file to a target system running the vulnerable tool
3. Victim or automated process opens the file with swftools
4. Overflow occurs and attacker-supplied code executes

How to detect it

Search process execution logs and file-access records for invocations of swftools binaries on untrusted inputs; monitor for segmentation faults or abnormal child-process creation during file handling.

What your security team should do

• Immediately inventory all systems for presence of swftools and remove or isolate them
• Block execution of the tool via application allow-listing
• Replace swftools workflows with supported utilities that handle the same file formats
• Add swftools binaries to endpoint monitoring for any future execution attempts