PYSEC-2026-1836

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PYSEC-2026-1836

Summary: PyPDF2 vulnerable to possible Infinite Loop when reading malformed objects

Details: ### 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/_data_structures.py::read_object`. 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.read_from_stream(stream, pdf) else: return NumberObject.read_from_stream(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.read_from_stream(stream, pdf) else: return NumberObject.read_from_stream(stream) else: raise PdfReadError( f"Invalid Elementary Object starting with {tok} @{stream.tell()}" ) ``` ### References * [pypdf issue #1329](https://github.com/py-pdf/pypdf/issues/1329) * [pypdf PR #1331](https://github.com/py-pdf/pypdf/pull/1331)

References: https://github.com/py-pdf/pypdf/security/advisories/GHSA-hm9v-vj3r-r55m, https://nvd.nist.gov/vuln/detail/CVE-2023-36807, https://github.com/py-pdf/pypdf/issues/1329, https://github.com/py-pdf/pypdf/pull/1331, https://github.com/py-pdf/pypdf/commit/e6531a25325e7e0174b6a1ba03b57320b5227f6b, https://github.com/py-pdf/pypdf, https://pypi.org/project/pypdf2, https://github.com/advisories/GHSA-hm9v-vj3r-r55m