Impact

An attacker who uses this vulnerability can craft a PDF which leads to an infinite loop if the PyPDF2 user wrote the following code:

from PyPDF2 import PdfFileReader, PdfFileWriter
from PyPDF2.pdf import ContentStream

reader = PdfFileReader("malicious.pdf", strict=False)
for page in reader.pages:
    ContentStream(page.getContents(), reader)

Patches

PyPDF2==1.27.5 and later are patched.

Credits to Sebastian Krause for finding (issue) and fixing (PR) it.