vulnerability / NVI-00010745 / Revision 1
Pillow: TarIO negative size field causes infinite CPU-spin loop
GitHub lists this reviewed advisory for Pillow. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
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02 / Applicability
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Pillow
source listed< 13.0.0
### Summary `TarIO.__init__` does not check that a tar header's size field is positive. A crafted header with a negative size makes it seek backward onto itself. This causes an infinite loop that uses 100% CPU and never returns. ### Details `TarIO.__init__` reads 512-byte tar headers one at a time, looking for a member with a given name. For each header it reads the size field and skips ahead to the next header: ```python size = int(s[124:135], 8) ... self.fh.seek((size + 511) & (~511), io.SEEK_CUR) ``` There is no check that size is zero or more. A tar header can set this field to a negative octal value. For size = -512, the seek offset comes out to exactly -512, which cancels the 512 bytes the loop had just read. The file position goes right back to where this loop step started. The loop only stops on end of file or when a header name starts with a null byte. Neither happens, since the same header keeps showing up again. The loop never ends on its own. ### Steps to reproduce This uses Tests/images/hopper.tar, a normal file already in the Pillow test suite. It only changes the size field of the first header. ```python from PIL import TarIO with open("Tests/images/hopper.tar
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04 / Limits
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05 / Provenance
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- GHSA-3j72-p6qg-6xp7 ↗
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- Revision 1 ·
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