pypdf and PyPDF2 possible Infinite Loop when a comment isn't followed by a character
Impact
An attacker who uses this vulnerability can craft a PDF which leads to an infinite loop if __parse_content_stream is executed. 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 text from such a PDF.
Example Code and a PDF that causes the issue:
from pypdf import PdfReader
# https://objects.githubusercontent.com/github-production-repository-file-5c1aeb/3119517/11367871?X-Amz-Algorithm=AWS4-HMAC-SHA256&X-Amz-Credential=AKIAIWNJYAX4CSVEH53A%2F20230627%2Fus-east-1%2Fs3%2Faws4_request&X-Amz-Date=20230627T201018Z&X-Amz-Expires=300&X-Amz-Signature=d71c8fd9181c4875f0c04d563b6d32f1d4da6e7b2e6be2f14479ce4ecdc9c8b2&X-Amz-SignedHeaders=host&actor_id=1658117&key_id=0&repo_id=3119517&response-content-disposition=attachment%3Bfilename%3DMiFO_LFO_FEIS_NOA_Published.3.pdf&response-content-type=application%2Fpdf
reader = PdfReader("MiFO_LFO_FEIS_NOA_Published.3.pdf")
page = reader.pages[0]
page.extract_text()The issue was introduced with https://github.com/py-pdf/pypdf/pull/969
Patches
The issue was fixed with https://github.com/py-pdf/pypdf/pull/1828
Workarounds
It is recommended to upgrade to pypdf>=3.9.0. PyPDF2 users should migrate to pypdf.
If you cannot update your version of pypdf, you should modify pypdf/generic/_data_structures.py:
OLD: while peek not in (b"\r", b"\n"):
NEW: while peek not in (b"\r", b"\n", b""):Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | pypdf | >= 3.1.0, < 3.9.0 | 3.9.0 |
| Python (PyPI) | pypdf2 | >= 2.2.0, <= 3.0.1 | no fix |
References
- https://github.com/py-pdf/pypdf/security/advisories/GHSA-4vvm-4w3v-6mr8
- https://nvd.nist.gov/vuln/detail/CVE-2023-36464
- https://github.com/py-pdf/pypdf/pull/1828
- https://github.com/py-pdf/pypdf/pull/969
- https://github.com/py-pdf/pypdf/commit/b0e5c689df689ab173df84dacd77b6fc3c161932
- https://github.com/py-pdf/pypdf
- https://github.com/py-pdf/pypdf/releases/tag/3.9.0
- https://pypi.org/project/pypdf2
- https://github.com/advisories/GHSA-4vvm-4w3v-6mr8
- https://pypi.org/project/pypdf
- CVSS vector
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-835- Platform
- Python (PyPI)
- Package
pypdf, pypdf2- Disclosed
- 30.06.2023
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-1835 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - PYSEC-2026-3008 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-4vvm-4w3v-6mr8 - CC BY 4.0
Vulnerability history: pypdf2
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 4
- First → latest
- 04.2022 06.2023
- Without a fix
- 1
- Exploited in attacks
- 0
Severity breakdown
- Medium 4
Disclosures per year
- 2022: 1
- 2023: 3
- 2024: 0
- 2025: 0
- 2026: 0
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pypdf and PyPDF2 possible Infinite Loop when a comment isn't followed by a character this entry
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