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: pypdf
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
- 54
- First → latest
- 06.2023 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 10
- Medium 41
- Low 3
Disclosures per year
- 2023: 2
- 2024: 0
- 2025: 4
- 2026: 48
-
pypdf and PyPDF2 possible Infinite Loop when a comment isn't followed by a character this entry
Know which vulnerabilities affect your application
With the DockRay integration and software inventory enabled, DockRay checks reported component versions against known vulnerabilities and notifies you about confirmed matches. Coverage depends on the supported technology and available advisory data.