{"id":"PYSEC-2026-1836","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\u003e3.1.0` 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)","aliases":["CVE-2023-36807","GHSA-hm9v-vj3r-r55m"],"modified":"2026-07-07T17:46:59.504076185Z","published":"2026-07-07T11:45:19.767457Z","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"}],"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"],"database_specific":{"source":"https://github.com/pypa/advisory-database/blob/main/vulns/pypdf2/PYSEC-2026-1836.yaml"}}],"schema_version":"1.7.5","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"}]}