{"id":"CVE-2023-36807","aliases":["GHSA-hm9v-vj3r-r55m","PYSEC-2026-1836"],"title":"PyPDF2 vulnerable to possible Infinite Loop when reading malformed objects","summary":"PyPDF2 vulnerable to possible Infinite Loop when reading malformed objects","severity":"medium","cvss":6.2,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","vendor":"pypdf2","product":"pypdf2","ecosystem":"pip","affected":["pypdf2 >= 2.10.5, < 2.10.6"],"patched":["pypdf2 2.10.6"],"published":"2023-06-30","updated":"2026-07-07","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-hm9v-vj3r-r55m","references":[{"url":"https://github.com/py-pdf/pypdf/security/advisories/GHSA-hm9v-vj3r-r55m"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2023-36807"},{"url":"https://github.com/py-pdf/pypdf/issues/1329"},{"url":"https://github.com/py-pdf/pypdf/pull/1331"},{"url":"https://github.com/py-pdf/pypdf/commit/e6531a25325e7e0174b6a1ba03b57320b5227f6b"},{"url":"https://github.com/py-pdf/pypdf"}],"tags":["osv","pip"],"epss":0.00573,"epssPercentile":0.46128,"ingestedAt":"2026-07-08T18:25:50.283Z","slug":"CVE-2023-36807","body":"## Overview\n\n### 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)\n\n## Affected packages\n\n- `pypdf2 >= 2.10.5, < 2.10.6`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `pypdf2 2.10.6`","depth":"sunlit","depthScore":34,"depthScoreParts":{"impact":34.1,"likelihood":0.1,"exploitation":0,"ransomware":0},"changes":[]}