Fix integer underflow in exif HEIF parsing #20630
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When pos.size is less than 2, the subtraction pos.size - 2 causes an unsigned integer underflow, resulting in a ~4GB allocation attempt. Add minimum size check (pos.size >= 2) to prevent the underflow.
ndossche
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Dec 2, 2025
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Thanks!
For the future, this should actually target the PHP-8.5 branch. That's because bugfixes always should target the lowest supported branch and we will merge upwards.
Doesn't matter now as I'll just cherry-pick into the right branch.
Leaving this open for a bit to see if anyone else has comments.
bukka
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Dec 2, 2025
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Can you add a test with that malicious image that you have?
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added a test in the second commit , it patches image029.heic to set extent_length=1 and verifies the fix handles it gracefully |
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When pos.size is less than 2, the subtraction pos.size - 2 causes an unsigned integer underflow, resulting in a ~4GB allocation attempt.
Add minimum size check (pos.size >= 2) to prevent the underflow.
Closes #20631