# CVE-2026-82398 — py-pdf pypdf

> As of 2026-09-01, CVE-2026-82398 is a Medium-severity (band derived from the CVSS v4.0 score, not stated by the CNA) vulnerability in py-pdf pypdf, CVSS v4.0 6.9, EPSS 0.3% (22.2th percentile). No Threadlinqs-tracked threat campaign has been attributed to CVE-2026-82398 as of 2026-09-01; the identifier is re-checked against the Threadlinqs threat corpus on every daily ingest.

**Last updated:** 2026-09-01

## What is CVE-2026-82398?

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.

The record classifies CVE-2026-82398 under weakness class [CWE-407](https://cwe.mitre.org/data/definitions/407.html). 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 35 days ago.

## Severity and exploitation probability

- **CVSS v4.0 base score:** 6.9 — Medium (derived from score) (`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`)
- **EPSS (FIRST):** 0.3% probability of exploitation in the next 30 days, higher than 22.2% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 4.3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-08-31, last modified 2026-09-01

## Is CVE-2026-82398 being exploited?

It currently carries a trending score of 35 in the Threadlinqs vulnerability feed.

## Affected products and versions

- **py-pdf**: pypdf

## How to fix CVE-2026-82398

No vendor patch reference has been recorded for CVE-2026-82398 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-82398

No threat campaign in the Threadlinqs corpus currently references CVE-2026-82398, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.

## Sources

Enriched from CVE.org, NVD, FIRST EPSS. Last verified by Threadlinqs on 2026-09-02. This product uses the NVD API but is not endorsed or certified by the NVD.

**Vendor advisory and patch**

- [github.com](https://github.com/py-pdf/pypdf/security/advisories/GHSA-fc8x-2rww-xw9m)

**Other references**

- [github.com](https://github.com/py-pdf/pypdf/pull/3947)
- [github.com (4959848e057e37c218dccad7465259210923faaa)](https://github.com/py-pdf/pypdf/commit/4959848e057e37c218dccad7465259210923faaa)
- [github.com (6.15)](https://github.com/py-pdf/pypdf/releases/tag/6.15.0)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-82398
Full detection coverage and IOCs for threats exploiting CVE-2026-82398 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp