Impact An attacker who uses this vulnerability can craft a PDF which leads to an infinite loop. This infinite loop blocks the current process and can utilize a single core of the CPU by 100%. It does not affect memory usage. That is, for example, the case if the user extracted metadata from such a malformed PDF.

Patches The issue was fixed with https://github.com/py-pdf/pypdf/pull/1331

Workarounds If you cannot update your version of PyPDF2 (preferably to pypdf>3.1.0 as PyPDF2 is deprecated), you should modify PyPDF2/generic/datastructures.py::readobject.

Replace:

python else: # number object OR indirect reference peek = stream.read(20) stream.seek(-len(peek), 1) # reset to start if IndirectPattern.match(peek) is not None: return IndirectObject.readfromstream(stream, pdf) else: return NumberObject.readfromstream(stream)

by

python elif tok in b"0123456789+-.": # number object OR indirect reference peek = stream.read(20) stream.seek(-len(peek), 1) # reset to start if IndirectPattern.match(peek) is not None: return IndirectObject.readfromstream(stream, pdf) else: return NumberObject.readfromstream(stream) else: raise PdfReadError( f"Invalid Elementary Object starting with {tok} @{stream.tell()}" )

References pypdf issue #1329 pypdf PR #1331