Pillow has a PDF Parsing Trailer Infinite Loop (DoS)

Impact

An attacker can supply a malicious PDF that causes the process to hang indefinitely, consuming 100% CPU and making the application unresponsive.

Patches

Patched version: 12.2.0.

PdfParser (introduced in Pillow 4.2.0) follows Prev pointers in PDF trailers to read cross-reference sections. If a
trailer's Prev pointer references an offset that has already been processed — either pointing to itself or forming a
longer cycle — the parser enters an infinite loop. Pillow now tracks previously processed trailer offsets and raises an
error if a cycle is detected.

Workarounds

Use any version but the affected versions: >= 4.2.0, < 12.2.0

Resources

• Fix: https://github.com/python-pillow/Pillow/pull/9519