PhpSpreadsheet is a pure PHP library for reading and writing spreadsheet files. Prior to 1.30.7, 2.1.19, 2.4.8, 3.10.8, and 5.10.0, Worksheet\Drawing::setPath validates only the initial external-image URL with setIsWhitelisted when setAllowExternalImages is enabled. The HTTP stream context permits PHP to follow a redirect without applying the callback to the redirected URL, so a permitted image host can redirect the server to an internal address and cause a blind GET request. The response body is not returned to the attacker because the reader validates the downloaded content as an image and removes the temporary file, but internal GET-driven endpoints, network reachability, and cloud metadata endpoints may be reached. This issue is fixed in versions 1.30.7, 2.1.19, 2.4.8, 3.10.8, and 5.10.0.
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