Raise SyntaxError instead of OverflowError for oversized JPEG 2000 box#9818
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nevercodecorrect wants to merge 7 commits into
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Raise SyntaxError instead of OverflowError for oversized JPEG 2000 box#9818nevercodecorrect wants to merge 7 commits into
nevercodecorrect wants to merge 7 commits into
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radarhere
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Jul 23, 2026
Update payload to match the one in def _accept(prefix: bytes) -> bool: Co-authored-by: Andrew Murray <3112309+radarhere@users.noreply.github.com>
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I've created nevercodecorrect#1 with a suggestion. |
Raise error when seeking, rather than when starting box
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Thank you. This actually makes more sense. I have applied it. |
radarhere
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Jul 23, 2026
Consider new position, not just offset
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The previous guard only rejected an oversized box length on the seek path in next_box_type(). A box that is descended into via read_boxes() (e.g. the jp2h header box) still passed the huge length to BytesIO.read(), leaking OverflowError out of Image.open(). Move the check to the point where the length is stored, so it protects both consumers of remaining_in_box: the seek in next_box_type() and the read in read_boxes(). Add regression tests that independently trigger the seek path and the read path.
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Fixes #9817 .
JPEG 2000's BoxReader accepts an extended 64-bit box length with no bound (the top-level reader has no known length), then passes it to fp.seek(..., SEEK_CUR), raising OverflowError from Image.open() on malformed input.
This is the JP2 counterpart of #9811 (TIFF, fixed in #9816). The box is now rejected as a malformed header (SyntaxError → UnidentifiedImageError), consistent with the plugin's other #checks.
Changes proposed in this pull request: