PYSEC-2026-1837 PyPDF2 quadratic runtime with malformed PDF missing xref marker

Impact An attacker who uses this vulnerability can craft a PDF which leads to unexpected long runtime. This quadratic runtime blocks the current process and can utilize a single core of the CPU by 100%. It does not affect memory usage. Patches https://github.com/py-pdf/pypdf/pull/808 Workarounds ...