SEC: Improve handling of partially broken PDF files #3594
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This changes does indeed contain mulitple fixes, but as all of them are about partially broken PDF files and possibly security-related, I decided to put them into one changeset. Besides renaming variables to make them more readable, this includes the following changes: 1. When searching through a PDF file which does not define a `/Root` entry in the trailer, while employing a large `/Size` value inside the trailer, this would lead to us trying to access each object number until the limit defined by `/Size` has been reached. This behavior can now be controlled by a new parameter to `PdfReader` which defaults to a more sensible default. 2. When a broken `startxref` table is discovered, we try to re-build it from scratch. This used a regex-based approach, which turned out to be problematic with files consisting of lots of whitespace characters. By replacing the regex-based approach by a manual search based upon `string.find()`, we were able to drastically improve the performance in such cases. 3. When flattening the pages of a PDF file, having one of the `/Kids` of the `/Pages` catalog entry reference the `/Pages` entry again would run until Python detects a recursion error itself. This has been changed to explicitly check for such cyclic references.
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Test file: root_object_recovery_limit.pdf |
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## main #3594 +/- ##
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+ Coverage 97.31% 97.35% +0.03%
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Files 55 55
Lines 9769 9815 +46
Branches 1780 1791 +11
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+ Hits 9507 9555 +48
+ Misses 155 153 -2
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## What's new ### Security (SEC) - Improve handling of partially broken PDF files (#3594) by @stefan6419846 ### Deprecations (DEP) - Block common page content modifications when assigned to reader (#3582) by @stefan6419846 ### New Features (ENH) - Embellishments to generated text appearance streams (#3571) by @PJBrs ### Bug Fixes (BUG) - Do not consider multi-byte BOM-like sequences as BOMs (#3589) by @stefan6419846 ### Robustness (ROB) - Avoid empty FlateDecode outputs without warning (#3579) by @stefan6419846 ### Documentation (DOC) - Add outlines documentation and link it in User Guide (#3511) by @mainuddin-md ### Developer Experience (DEV) - Add PyPy 3.11 to test matrix and benchmarks (#3574) by @rassie ### Maintenance (MAINT) - Fix compatibility with Pillow >= 12.1.0 (#3590) by @stefan6419846 [Full Changelog](6.5.0...6.6.0)
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This changes does indeed contain multiple fixes, but as all of them are about partially broken PDF files and possibly security-related, I decided to put them into one changeset.
Besides renaming variables to make them more readable, this includes the following changes:
When searching through a PDF file which does not define a
/Rootentry in the trailer, while employing a large/Sizevalue inside the trailer, this would lead to us trying to access each object number until the limit defined by/Sizehas been reached. This behavior can now be controlled by a new parameter toPdfReaderwhich defaults to a more sensible default.When a broken
startxreftable is discovered, we try to re-build it from scratch. This used a regex-based approach, which turned out to be problematic with files consisting of lots of whitespace characters. By replacing the regex-based approach by a manual search based uponstring.find(), we were able to drastically improve the performance in such cases.When flattening the pages of a PDF file, having one of the
/Kidsof the/Pagescatalog entry reference the/Pagesentry again would run until Python detects a recursion error itself. This has been changed to explicitly check for such cyclic references.