Summary
Workarounds
from pypdf import PdfReader, PdfWriter
# Instead of
reader = PdfReader("file.pdf")
# use the strict mode:
reader = PdfReader("file.pdf", strict=True)
# Instead of
writer = PdfWriter(clone_from="file.pdf")
# use an explicit strict reader:
writer = PdfWriter(clone_from=PdfReader("file.pdf", strict=True))
Resources
This issue has been fixed in #3594.
Impact
An attacker who exploits this vulnerability can craft a PDF which leads to possibly long runtimes for invalid startxref entries. When rebuilding the cross-reference table, PDF files with lots of whitespace characters become problematic. Only the non-strict reading mode is affected.
Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
Remediation advice
This has been fixed in pypdf==6.6.0.
Frequently Asked Questions
- What is CVE-2026-22691? CVE-2026-22691 is a low-severity uncontrolled resource consumption vulnerability in pypdf (pip), affecting versions < 6.6.0. It is fixed in 6.6.0. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
- Which versions of pypdf are affected by CVE-2026-22691? pypdf (pip) versions < 6.6.0 is affected.
- Is there a fix for CVE-2026-22691? Yes. CVE-2026-22691 is fixed in 6.6.0. Upgrade to this version or later.
- Is CVE-2026-22691 exploitable, and should I be worried? Whether CVE-2026-22691 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-22691 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-22691? Upgrade
pypdfto 6.6.0 or later.