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7.3
pypdf Can Take a Long Time to Process Malformed PDFs
CVE-2026-27026
GHSA-9mvc-8737-8j8h
CVE-2026-27026
Summary
If you use pypdf, an attacker could create a PDF that would take a long time to process. This could potentially cause delays or slow down your system. Update to version 6.7.1 or later to fix this issue.
What to do
- Update pypdf to version 6.7.1.
Affected software
| Vendor | Product | Affected versions | Fix available |
|---|---|---|---|
| – | pypdf | <= 6.7.1 | 6.7.1 |
| pypdf_project | pypdf | <= 6.7.1 | – |
Original title
pypdf possibly has long runtimes for malformed FlateDecode streams
Original description
pypdf is a free and open-source pure-python PDF library. Prior to 6.7.1, an attacker who uses this vulnerability can craft a PDF which leads to long runtimes. This requires a malformed /FlateDecode stream, where the byte-by-byte decompression is used. This vulnerability is fixed in 6.7.1.
nvd CVSS3.1
5.5
nvd CVSS4.0
6.9
Vulnerability type
CWE-770
Allocation of Resources Without Limits
- https://nvd.nist.gov/vuln/detail/CVE-2026-27026
- https://github.com/advisories/GHSA-9mvc-8737-8j8h
- https://github.com/py-pdf/pypdf/commit/7905842d833f899f1d3228af7e7467ad80277016 Patch
- https://github.com/py-pdf/pypdf/pull/3644 Issue Tracking Patch
- https://github.com/py-pdf/pypdf/releases/tag/6.7.1 Product Release Notes
- https://github.com/py-pdf/pypdf/security/advisories/GHSA-9mvc-8737-8j8h Patch Vendor Advisory
- https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/27xxx/CVE-2026-27026... Vendor Advisory
Published: 20 Feb 2026 · Updated: 12 Mar 2026 · First seen: 6 Mar 2026