CVE-2026-27026 py-pdf CVE debrief

Who should care

Defenders responsible for maintaining and securing systems that use the pypdf library should prioritize updating to version 6.7.1 or later to prevent potential denial-of-service attacks.

Why it matters

CVE-2026-27026 is a vulnerability in the pypdf library that can lead to long runtimes when processing a specially crafted PDF, potentially causing performance issues. Defenders should prioritize updating to version 6.7.1 or later to prevent potential denial-of-service attacks.

• Potential denial-of-service attacks through crafted PDFs
• Performance issues due to long runtimes
• Need for input validation and error handling in PDF processing workflows

Technical summary

The pypdf library is vulnerable to a denial-of-service attack when processing a specially crafted PDF. An attacker can craft a PDF that leads to long runtimes, potentially causing performance issues. This vulnerability is fixed in version 6.7.1. The vulnerability is related to a malformed /FlateDecode stream, where the byte-by-byte decompression is used. Defenders should prioritize updating to version 6.7.1 or later to prevent potential denial-of-service attacks. The vulnerability requires a crafted PDF to exploit, and defenders should review and monitor PDF processing workflows for potential denial-of-service attacks.

Defensive priority

Defenders should prioritize updating to version 6.7.1 or later to prevent potential denial-of-service attacks.

Recommended defensive actions

• Update to pypdf version 6.7.1 or later
• Review and monitor PDF processing workflows for potential denial-of-service attacks
• Implement input validation and error handling for PDF processing
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• technicalSummary

Evidence notes

The vulnerability is described in the CVE record and NVD entry. The fix is available in version 6.7.1 of the pypdf library. The CVE record was published on 2026-02-20T22:16:29.023Z and has not been modified since then. The vulnerability is related to a malformed /FlateDecode stream, where the byte-by-byte decompression is used. The NVD entry provides additional information on the vulnerability, including its CVSS score and severity.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.