Security (5/5): outline cycle + XMP entity expansion — CVE-2026-24688, CVE-2026-40260#5
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A crafted document outline whose /Next chain loops back to an already-visited node made PdfReader._get_outlines walk forever (CWE-835). Track visited node ids; stop (with a warning) on a repeat, and pass a copy of the visited set into the /First sub-outline recursion so shared sub-trees still render. The new visited parameter is a trailing keyword default, so the public signature is unchanged. Mirrors upstream pypdf 6.6.2 (PR py-pdf#3610). Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
XmpInformation parsed untrusted XMP metadata with xml.dom.minidom parseString, which permits XML entity declarations. libexpat blocks exponential expansion but not quadratic expansion, so a crafted XMP packet could exhaust memory (CWE-776). Parse via a namespace-aware ExpatBuilderNS subclass that installs an EntityDeclHandler rejecting any entity declaration with ExpatError. Mirrors upstream pypdf 6.10.0 (PR py-pdf#3724); xml.dom.expatbuilder is available on Python 2.7. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
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Pull request overview
Backport security fixes to the PyPDF2 1.28.6.x line to mitigate two moderate CVEs: (1) prevent infinite loops when traversing cyclic outline /Next chains, and (2) reject XML entity declarations when parsing XMP metadata to prevent entity-expansion DoS.
Changes:
- Add cycle detection (
visitedset) to the outline traversal inPdfReader._get_outlines. - Replace XMP parsing with an
ExpatBuilderNS-based parser that rejects entity declarations. - Add regression tests for both CVEs.
Reviewed changes
Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.
| File | Description |
|---|---|
PyPDF2/_reader.py |
Adds visited-node tracking to stop outline walking on cycles. |
PyPDF2/xmp.py |
Introduces a safe XMP parser that refuses entity declarations. |
Tests/test_security_outline.py |
Adds a regression test ensuring cyclic outlines terminate. |
Tests/test_security_xmp.py |
Adds regression tests verifying normal XMP parses and entity declarations are rejected. |
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Part 5 of 5 of the PyPDF2 1.28.6 security backport, targeting
1.28.6.x._reader.py/Nextwalk against cyclesxmp.pyBackported from upstream pypdf 6.6.2 / 6.10.0; Py2.7-safe (
xml.dom.expatbuilderis available on 2.7). New tests:Tests/test_security_outline.py,Tests/test_security_xmp.py(3). Validated under Python 2.7.18 — no regressions.🤖 Generated with Claude Code