What’s Vulnerable › Vulnerabilities

CVE-2026-102997: pypdf: Possible long runtimes for partially malformed FlateDecode streams (Follow-up)

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.3% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-09-30 · updated 2026-10-05
• Weakness: CWE-400

Description

pypdf is a free and open-source pure-python PDF library. Prior to 6.18.1, a crafted PDF containing a partially malformed /FlateDecode stream with padded data can force pypdf/filters.py to use inefficient byte-by-byte decompression while the earlier recovery counter fails to advance for bytes that successfully decode, causing long runtimes and application unavailability. This is a residual issue after the malformed FlateDecode recovery fix. This issue is fixed in version 6.18.1.

Affected products

• py-pdf pypdf: before 6.18.1 — fixed in 6.18.1

How to fix

Upgrade to a fixed version: py-pdf pypdf 6.18.1. Check the vendor advisory for mitigations.

References

• https://github.com/py-pdf/pypdf/commit/d9d38cf99b115deb562d3b68f36c33027bc04f79
• https://github.com/py-pdf/pypdf/pull/4073
• https://github.com/py-pdf/pypdf/releases/tag/6.18.1
• https://github.com/py-pdf/pypdf/security/advisories/GHSA-jw7q-gvrg-4vj3

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