PyPDF2 vulnerable to possible Infinite Loop when reading malformed objects
Impact
An attacker who uses this vulnerability can craft a PDF which leads to an infinite loop. This infinite loop blocks the current process and can utilize a single core of the CPU by 100%. It does not affect memory usage. That is, for example, the case if the user extracted metadata from such a malformed PDF.
Patches
The issue was fixed with https://github.com/py-pdf/pypdf/pull/1331
Workarounds
If you cannot update your version of PyPDF2 (preferably to pypdf>3.1.0 as PyPDF2 is deprecated), you should modify PyPDF2/generic/_data_structures.py::read_object.
Replace:
else:
# number object OR indirect reference
peek = stream.read(20)
stream.seek(-len(peek), 1) # reset to start
if IndirectPattern.match(peek) is not None:
return IndirectObject.read_from_stream(stream, pdf)
else:
return NumberObject.read_from_stream(stream)by
elif tok in b"0123456789+-.":
# number object OR indirect reference
peek = stream.read(20)
stream.seek(-len(peek), 1) # reset to start
if IndirectPattern.match(peek) is not None:
return IndirectObject.read_from_stream(stream, pdf)
else:
return NumberObject.read_from_stream(stream)
else:
raise PdfReadError(
f"Invalid Elementary Object starting with {tok} @{stream.tell()}"
)References
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | pypdf2 | >= 2.10.5, < 2.10.6 | 2.10.6 |
References
- https://github.com/py-pdf/pypdf/security/advisories/GHSA-hm9v-vj3r-r55m
- https://nvd.nist.gov/vuln/detail/CVE-2023-36807
- https://github.com/py-pdf/pypdf/issues/1329
- https://github.com/py-pdf/pypdf/pull/1331
- https://github.com/py-pdf/pypdf/commit/e6531a25325e7e0174b6a1ba03b57320b5227f6b
- https://github.com/py-pdf/pypdf
- https://pypi.org/project/pypdf2
- https://github.com/advisories/GHSA-hm9v-vj3r-r55m
- CVSS vector
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-835- Platform
- Python (PyPI)
- Package
pypdf2- Disclosed
- 30.06.2023
- Updated
- 11.10.2026 13:18
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-1836 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-hm9v-vj3r-r55m - CC BY 4.0
Vulnerability history: pypdf2
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
- 4
- First → latest
- 04.2022 06.2023
- Without a fix
- 1
- Exploited in attacks
- 0
Severity breakdown
- Medium 4
Disclosures per year
- 2022: 1
- 2023: 3
- 2024: 0
- 2025: 0
- 2026: 0
-
PyPDF2 vulnerable to possible Infinite Loop when reading malformed objects this entry
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