pypdf has possible long runtimes for malformed startxref
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.
Patches
This has been fixed in pypdf==6.6.0.
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.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | pypdf | < 6.6.0 | 6.6.0 |
References
- https://github.com/py-pdf/pypdf/security/advisories/GHSA-4f6g-68pf-7vhv
- https://nvd.nist.gov/vuln/detail/CVE-2026-22691
- https://github.com/py-pdf/pypdf/pull/3594
- https://github.com/py-pdf/pypdf/commit/294165726b646bb7799be1cc787f593f2fdbcf45
- https://github.com/py-pdf/pypdf
- https://github.com/py-pdf/pypdf/releases/tag/6.6.0
- https://pypi.org/project/pypdf
- https://github.com/advisories/GHSA-4f6g-68pf-7vhv
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U- Weakness (CWE)
CWE-1333, CWE-400- Platform
- Python (PyPI)
- Package
pypdf- Disclosed
- 09.01.2026
- Updated
- 11.10.2026 13:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-1828 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-4f6g-68pf-7vhv - CC BY 4.0
Vulnerability history: pypdf
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 51
- First → latest
- 06.2023 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 10
- Medium 38
- Low 3
Disclosures per year
- 2023: 2
- 2024: 0
- 2025: 4
- 2026: 45
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pypdf has possible long runtimes for malformed startxref this entry
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