KITFORMA · EDITORIAL ANSWER
How can I extract an uploaded ZIP without allowing paths outside its destination?
KitForma editorial guide. Archive member names are input data, not trusted filesystem paths. Absolute paths, parent traversal and platform-specific separators require validation before writing.
Step-by-step answer
Archive member names are input data, not trusted filesystem paths. Absolute paths, parent traversal and platform-specific separators require validation before writing.
Resolve each intended destination beneath a dedicated extraction root and reject any member escaping it. Also bound entry count, uncompressed size and compression ratio, and decide explicitly whether links are allowed. Test harmless fixtures containing
../outside.txt, absolute names and oversized declared sizes. Do not assume path checks alone prevent archive bombs or overwrite races. Use a maintained extraction library, an isolated temporary directory and a policy that refuses unexpected file types before moving verified output into permanent storage.Sources and verification
Sources checked:
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