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Raise an error if the trailer chain loops back on itself (#9519)

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Hugo van Kemenade 2026-04-01 00:03:15 +03:00 committed by GitHub
parent 3cb854e8b2
commit 3bf614e4b8
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3 changed files with 13 additions and 2 deletions
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Tests/images/trailer_loop.pdf Normal file
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5
Tests/test_pdfparser.py
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@ -125,3 +125,8 @@ def test_duplicate_xref_entry() -> None:
pdf = PdfParser("Tests/images/duplicate_xref_entry.pdf")
assert pdf.xref_table.existing_entries[6][0] == 1197
pdf.close()
def test_trailer_loop() -> None:
with pytest.raises(PdfFormatError, match="trailer loop found"):
PdfParser("Tests/images/trailer_loop.pdf")

10
src/PIL/PdfParser.py
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@ -685,7 +685,9 @@ class PdfParser:
if b"Prev" in self.trailer_dict:
self.read_prev_trailer(self.trailer_dict[b"Prev"])
def read_prev_trailer(self, xref_section_offset: int) -> None:
def read_prev_trailer(
self, xref_section_offset: int, processed_offsets: list[int] = []
) -> None:
assert self.buf is not None
trailer_offset = self.read_xref_table(xref_section_offset=xref_section_offset)
m = self.re_trailer_prev.search(
@ -700,7 +702,11 @@ class PdfParser:
)
trailer_dict = self.interpret_trailer(trailer_data)
if b"Prev" in trailer_dict:
self.read_prev_trailer(trailer_dict[b"Prev"])
processed_offsets.append(xref_section_offset)
check_format_condition(
trailer_dict[b"Prev"] not in processed_offsets, "trailer loop found"
)
self.read_prev_trailer(trailer_dict[b"Prev"], processed_offsets)
re_whitespace_optional = re.compile(whitespace_optional)
re_name = re.compile(