---
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: 0.44966
ingestedAt: '2026-07-08T18:25:50.283Z'
---

## Overview

### 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)

## Affected packages

- `pypdf2 >= 2.10.5, < 2.10.6`

## Remediation

Upgrade to a patched release:

- `pypdf2 2.10.6`