Form XObject with malformed /BBox crashes extraction (ValueError: not enough values to unpack)

[assinscreedFC]

Summary

extract_text (and any layout extraction) raises ValueError: not enough values to unpack (expected 4, got 2) on PDFs that contain a form XObject whose /BBox is not the four-number rectangle required by the spec.

Root cause

In PDFPageInterpreter.do_Do (pdfminer/pdfinterp.py), a form XObject's /BBox is passed straight to begin_figure → LTFigure.__init__ (pdfminer/layout.py), which unpacks it with (x, y, w, h) = bbox. A /BBox with a different number of elements (e.g. [0 0]) therefore raises a ValueError and aborts the whole extraction. The length of /BBox is never validated.

Minimal reproduction

A form XObject with /BBox [0 0]:

import io
import pdfminer.high_level

pdf = (
    b"%PDF-1.4\n"
    b"1 0 obj <</Type/Catalog/Pages 2 0 R>> endobj\n"
    b"2 0 obj <</Type/Pages/Kids[3 0 R]/Count 1>> endobj\n"
    b"3 0 obj <</Type/Page/Parent 2 0 R/MediaBox[0 0 200 200]"
    b"/Resources<</XObject<</Fm0 4 0 R>>>>/Contents 5 0 R>> endobj\n"
    b"4 0 obj <</Type/XObject/Subtype/Form/FormType 1/BBox [0 0]"
    b"/Resources<<>>/Length 3>>\nstream\nq Q\nendstream endobj\n"
    b"5 0 obj <</Length 7>>\nstream\n/Fm0 Do\nendstream endobj\n"
    b"trailer<</Root 1 0 R>>\n%%EOF"
)
pdfminer.high_level.extract_text(io.BytesIO(pdf))
# ValueError: not enough values to unpack (expected 4, got 2)

(Real-world PDFs from some generators ship such non-conformant form bboxes; this also surfaces downstream in pdfplumber and tools built on it such as markitdown.)

Expected

A non-conformant /BBox should not crash extraction. In non-STRICT mode the malformed bbox should be tolerated (the rest of the document still extracted); STRICT mode may raise.

Environment

• pdfminer.six 20251230, Python 3.13

I have a fix + regression test ready and will open a PR referencing this issue.