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CVE-2026-119209: pypdf: Possible large memory usage when parsing cross-reference streams

• Severity: medium (CVSS 5.5 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: 2026-10-29 · updated 2026-10-31
• Weakness: CWE-400

Description

pypdf is a free and open-source pure-python PDF library. Prior to 6.21.3, pypdf can consume excessive memory while opening a crafted PDF containing cross-reference streams that declare very large entry counts. Highly compressible streams and /Prev chains can multiply the number of parsed entries across a document, while negative /Index counts can bypass the existing per-stream clamp. This issue is fixed in version 6.21.3.

Affected products

• py-pdf pypdf: before 6.21.3 — fixed in 6.21.3
• py-pdf pypdf: before 6.21.3

How to fix

Upgrade to a fixed version: py-pdf pypdf 6.21.3. Check the vendor advisory for mitigations.

References

• https://github.com/py-pdf/pypdf/commit/a93fe3a901fd00af38f0a105c3ba7175fa72dcb4
• https://github.com/py-pdf/pypdf/pull/4269
• https://github.com/py-pdf/pypdf/releases/tag/6.21.3
• https://github.com/py-pdf/pypdf/security/advisories/GHSA-x3rh-gjgm-fmqc

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