CVE-2023-36464: Infinite Loop when a comment isn't followed by a character in pypdf

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: yes
Published: 2023-06-27 · updated 2026-06-17
Weakness: CWE-835

Description

pypdf is an open source, pure-python PDF library. In affected versions an attacker may craft a PDF which leads to an infinite loop if `__parse_content_stream` is executed. That is, for example, the case if the user extracted text from such a PDF. This issue was introduced in pull request #969 and resolved in pull request #1828. Users are advised to upgrade. Users unable to upgrade may modify the line `while peek not in (b"\r", b"\n")` in `pypdf/generic/_data_structures.py` to `while peek not in (b"\r", b"\n", b"")`.

Affected products

Pypdf2 Project Pypdf2: from 2.2.0
py-pdf pypdf: before 3.9.0 — fixed in 3.9.0

How to fix

Upgrade to a fixed version: py-pdf pypdf 3.9.0. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2023-36464 or the next vulnerability affects your stack