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Raise ValueError for truncated gAMA and cHRM PNG chunks #9880

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Merged
radarhere merged 2 commits into from
Aug 20, 2026
+13 −2
Merged

Raise ValueError for truncated gAMA and cHRM PNG chunks #9880

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8084c71
Raise a truncated chunk error for a short gAMA chunk
VenishPaneliya Aug 20, 2026
cc1602b
Raise a truncated chunk error for a short cHRM chunk
VenishPaneliya Aug 20, 2026
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3 changes: 2 additions & 1 deletion Tests/test_file_png.py
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Original file line number Diff line number Diff line change
Expand Up @@ -700,7 +700,8 @@ def test_padded_idat(self, monkeypatch: pytest.MonkeyPatch) -> None:
assert_image_equal_tofile(im, "Tests/images/bw_gradient.png")

@pytest.mark.parametrize(
"cid", (b"IHDR", b"sRGB", b"pHYs", b"acTL", b"fcTL", b"fdAT")
"cid",
(b"IHDR", b"gAMA", b"cHRM", b"sRGB", b"pHYs", b"acTL", b"fcTL", b"fdAT"),
)
def test_truncated_chunks(
self, cid: bytes, monkeypatch: pytest.MonkeyPatch
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12 changes: 11 additions & 1 deletion src/PIL/PngImagePlugin.py
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Original file line number Diff line number Diff line change
Expand Up @@ -521,6 +521,11 @@ def chunk_gAMA(self, pos: int, length: int) -> bytes:
# gamma setting
assert self.fp is not None
s = ImageFile._safe_read(self.fp, length)
if length < 4:
if ImageFile.LOAD_TRUNCATED_IMAGES:
return s
msg = "Truncated gAMA chunk"
raise ValueError(msg)
self.im_info["gamma"] = i32(s) / 100000.0
return s

Expand All @@ -530,7 +535,12 @@ def chunk_cHRM(self, pos: int, length: int) -> bytes:

assert self.fp is not None
s = ImageFile._safe_read(self.fp, length)
raw_vals = struct.unpack(f">{len(s) // 4}I", s)
if length < 32:
if ImageFile.LOAD_TRUNCATED_IMAGES:
return s
msg = "Truncated cHRM chunk"
raise ValueError(msg)
raw_vals = struct.unpack(">8I", s[:32])
self.im_info["chromaticity"] = tuple(elt / 100000.0 for elt in raw_vals)
return s

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