CVE-2023-29950

What it actually does

Heap buffer overflow in enumerateUsedIDs_fillstyle allows out-of-bounds memory writes when processing a crafted SWF file, resulting in process crash.

Why it matters to the business

Attackers who can supply SWF content can trigger denial of service against any Winter CMS instance that invokes the affected swfrender code, causing temporary loss of service until the process is restarted.

How an attack unfolds

An attacker crafts a malicious SWF file that triggers the overflow inside enumerateUsedIDs_fillstyle, then causes the Winter CMS application to process that file through its media or asset handling paths that call swfrender.

How to fix it

Upgrade Winter CMS to the commit fa50b4c7489b67ea80072f8ac9fe5294fce1df1c or later; rebuild any local swftools/swfrender binaries from the patched source.

How to confirm the fix worked

Confirm the running swfrender binary or Winter CMS source tree contains commit fa50b4c7489b67ea80072f8ac9fe5294fce1df1c; re-test media upload/render paths with known-good SWF files.

Typical attack path

1. Identify Winter CMS instance that processes user-supplied or externally fetched SWF files
2. Craft SWF file that overflows the heap buffer in enumerateUsedIDs_fillstyle
3. Upload or cause the CMS to fetch and render the malicious SWF
4. Observe process crash and service interruption

How to detect it

Review web-server and application logs for repeated SWF uploads or render requests that coincide with worker process restarts or segmentation faults; correlate with file-upload endpoints that accept .swf extensions.

What your security team should do

• Immediately update Winter CMS to the patched commit if any SWF processing is enabled
• Disable or sandbox SWF rendering until the update is applied
• Monitor for availability alerts on CMS worker processes