id: PYSEC-2026-1836
published: "2026-07-07T11:45:19.767457Z"
modified: "2026-07-07T11:45:19.767457Z"
aliases:
- CVE-2023-36807
- GHSA-hm9v-vj3r-r55m
summary: PyPDF2 vulnerable to possible Infinite Loop when reading malformed objects
details: "### Impact\nAn attacker who uses this vulnerability can craft a PDF which leads to an infinite loop.\nThis 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.\n\n### Patches\nThe issue was fixed with https://github.com/py-pdf/pypdf/pull/1331\n\n### Workarounds\nIf 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`.\n\nReplace:\n\n```python\n    else:\n        # number object OR indirect reference\n        peek = stream.read(20)\n        stream.seek(-len(peek), 1)  # reset to start\n        if IndirectPattern.match(peek) is not None:\n            return IndirectObject.read_from_stream(stream, pdf)\n        else:\n            return NumberObject.read_from_stream(stream)\n```\n\nby\n\n```python\n    elif tok in b\"0123456789+-.\":\n        # number object OR indirect reference\n        peek = stream.read(20)\n        stream.seek(-len(peek), 1)  # reset to start\n        if IndirectPattern.match(peek) is not None:\n            return IndirectObject.read_from_stream(stream, pdf)\n        else:\n            return NumberObject.read_from_stream(stream)\n    else:\n        raise PdfReadError(\n            f\"Invalid Elementary Object starting with {tok} @{stream.tell()}\"\n        )\n```\n\n### References\n* [pypdf issue #1329](https://github.com/py-pdf/pypdf/issues/1329)\n* [pypdf PR #1331](https://github.com/py-pdf/pypdf/pull/1331)"
affected:
- package:
    name: pypdf2
    ecosystem: PyPI
    purl: pkg:pypi/pypdf2
  ranges:
  - type: ECOSYSTEM
    events:
    - introduced: 2.10.5
    - fixed: 2.10.6
  versions:
  - 2.10.5
references:
- type: WEB
  url: https://github.com/py-pdf/pypdf/security/advisories/GHSA-hm9v-vj3r-r55m
- type: ADVISORY
  url: https://nvd.nist.gov/vuln/detail/CVE-2023-36807
- type: WEB
  url: https://github.com/py-pdf/pypdf/issues/1329
- type: WEB
  url: https://github.com/py-pdf/pypdf/pull/1331
- type: FIX
  url: https://github.com/py-pdf/pypdf/commit/e6531a25325e7e0174b6a1ba03b57320b5227f6b
- type: PACKAGE
  url: https://github.com/py-pdf/pypdf
- type: PACKAGE
  url: https://pypi.org/project/pypdf2
- type: ADVISORY
  url: https://github.com/advisories/GHSA-hm9v-vj3r-r55m
severity:
- type: CVSS_V3
  score: CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H