CVE-2026-33123 py-pdf CVE debrief

Who should care

Defenders responsible for systems using the pypdf library should assess exposure and prioritize upgrading to version 6.9.1 or later. This includes operators, platform administrators, vulnerability management teams, and security teams who need to review and update affected systems to prevent potential denial-of-service attacks.

Why it matters

Defenders should prioritize upgrading to version 6.9.1 or later to prevent potential denial-of-service attacks. The vulnerability allows an attacker to craft a malicious PDF leading to long runtimes and/or large memory usage.

• Potential denial-of-service attacks through malicious PDFs
• Increased memory usage and long runtimes

Technical summary

The pypdf library is vulnerable to a denial-of-service attack when processing malicious PDFs. The issue is fixed in version 6.9.1. The vulnerability allows an attacker to craft a malicious PDF leading to long runtimes and/or large memory usage. This can be achieved by accessing an array-based stream with many entries, which can cause performance issues and increased memory usage. Defenders should prioritize upgrading to version 6.9.1 or later to prevent potential denial-of-service attacks. The vulnerability has a CVSS score of 5.1 and a severity of MEDIUM.

Defensive priority

Defenders should prioritize upgrading to version 6.9.1 or later to prevent potential denial-of-service attacks.

Recommended defensive actions

• Upgrade to version 6.9.1 or later
• Review and update affected systems
• Monitor for potential denial-of-service attacks
• Review compensating controls for exposed systems
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and NVD entry provide information on the vulnerability, its impact, and the fixed version. The vulnerability affects the pypdf library, which is a free and open-source pure-python PDF library. The issue has been reported and verified through various sources, including the CVE Program and NVD. However, the exact scope of affected systems and potential impact on defenders is not fully known and requires further verification.

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.