fix: NULL pointer dereference in multipart parser (GHSA-8m8p-vhxc-jmjw)#450
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When the multipart parser matched '--<boundary>' inside file data, it freed _itemBuffer but left _itemIsFile = true. If the next byte was neither the closing '--' nor a clean '\r\n', the rewind logic in DASH3_OR_RETURN2 / EXPECT_FEED2 called itemWriteByte(), which dereferenced the now-NULL _itemBuffer via _handleUploadByte, causing a StoreProhibited crash on ESP32 (remote DoS, CWE-476 / CWE-672). Fix: - Reset _itemIsFile = false immediately after freeing _itemBuffer in BOUNDARY_OR_DATA, so the rewind logic writes to _itemValue (String) instead of the freed buffer. - Add a NULL guard in _handleUploadByte as defense-in-depth. Added test case 11 in MultiPart.ino to reproduce and verify the fix.
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Fix for security advisory: GHSA-8m8p-vhxc-jmjw
When the multipart parser matched '--' inside file data, it freed _itemBuffer but left _itemIsFile = true. If the next byte was neither the closing '--' nor a clean '\r\n', the rewind logic in DASH3_OR_RETURN2 / EXPECT_FEED2 called itemWriteByte(), which dereferenced the now-NULL _itemBuffer via _handleUploadByte, causing a StoreProhibited crash on ESP32 (remote DoS, CWE-476 / CWE-672).
Fix:
Added test case 11 in MultiPart.ino to reproduce and verify the fix.