Security

We strive to provide a library with secure defaults.

Configuration

Global

pypdf currently employs a set of global configuration values, whose descriptions and defaults are available at Configuration. They internally rely on contextvars.

from pypdf import Configuration, PdfReader, apply_configuration, overwrite_configuration

# Limit the values to the current scope.
# The changed configuration value will be reset when exiting the context manager.
with apply_configuration(maximum_declared_stream_length=10_000):
    reader = PdfReader("example.pdf")
    for page in reader.pages:
        # Do something with the page.
        pass

# Overwrite the values globally.
overwrite_configuration(maximum_declared_stream_length=5_000)
reader = PdfReader("example.pdf")
for page in reader.pages:
    # Do something with the page.
    pass

Reading

pypdf currently employs the following reading limits on PdfReader instances:

root_object_recovery_limit limits the number of objects to read before stopping with Root object recovery in non-strict mode. It defaults to 10 000. Setting it to None will fully disable this limit.

If you want to employ custom limits for the PdfWriter as well, the currently preferred way is to initialize it from the reader, id est something like PdfWriter(clone_from=PdfReader("file.pdf", root_object_recovery_limit=42)).

For PdfWriter instances, the following limits are employed for incremental reading:

incremental_clone_object_count_limit limits the number of objects to read during cloning. It defaults to 500 000. Setting it to None will fully disable this limit.
incremental_clone_object_id_limit limits the maximum object ID to read during cloning. It defaults to 1 000 000. Setting it to None will fully disable this limit.

Reporting possible vulnerabilities

Please refer to our security policy.

Invalid reports

Exceptions

Most exceptions raised by our code are considered bugs or robustness issues and can be reported publicly. We consider it the task of the library user to catch exceptions which could cause their service to crash, although we try to only raise a known set of exception types.

Cryptographic functions

We receive reports about possibly insecure cryptography from time to time. This includes the following aspects:

Using the ARC4 cipher
Using the AES cipher in ECB mode
Using MD5 for hashing

These are requirements of the PDF standard, which we need to achieve the greatest compatibility with. Although some of them might be deprecated in PDF 2.0, the PDF 2.0 adoption rate is very low and legacy documents need to be supported.

XML parsing

We use xml.minidom for parsing XMP information. Given recent Python versions built against recent Expat versions, the usual attacks (exponential entity expansion and external entity expansion) should not be possible. We have corresponding tests in place to ensure this for the platforms our tests run against.

For some details, see the official documentation and the README for defusedxml.

Please note that automated scanners tend to still flag any direct imports of XML modules from the Python standard library as unsafe. There have been discussions about this being outdated already, but they are still being flagged.