Teraz potrzebujemy sprawić żeby plik png był też plikiem ZIP. Palette needs to come as triplets (for RGB) so we prepare a function to convert given binary payload into palette bytes string:ī = ["".format(ord(c)) for c in png.content)) Palette is very interesting because it is stored in consecutive bytes inside the PNG file. The edit feature provides API to set palette and pixels using JSON. We couldn't simply upload our rigged png file since it would be processed by the page, but we could edit it afterwards. It turns out a proper png file can be also a proper zip file!Īnd the `zip://` does not take extension into consideration so it can unzip a `.png` file just as well, as long as it's a zip file. This fixes the problem with file extension since we can control extension of the file inside zip.īut there is still problem with how to upload a zip file when we can only upload a valid image file. This means that if we could upload a zip archive with a php file inside to the webpage, we could then include it via:Īnd this would unpack the archive and include `file_inside.php` file to the page. This means that it's possible to run: `zip://path_to_zip#file_name` as `include()` argument and this way you can include the file from zip. There is a `zip://` wrapper which enables unzipping archives on the fly and provides access to the stored files. It took us a while to figure out the approach but then we come up with an idea that if wrappers helped us once, they might help again. The first issue we had to overcome was the ability to include a file of our choosing. We can manually set palette and image pixels using the built-in image edit feature of the webpage. The image is stripped from metadata so no way to smuggle something in exif We can only upload a proper image to the webpage Any uploaded image will always have `.png` extension The page only includes `.php` files because the extension is always added, and it's a new PHP so no null-byte poisoning Sources analysis brings us to conclusion that: This way we extract all source files (see (src) directory). We use php filter-wrapper `php://filter/read=convert.base64-encode/resource=` to force base64 encoding of the included pages eg: We try to put some other values there and we determine that it's a file inclusion for `.php` files. Those icons are then placed in /uploads directory with random name as png files.įirst thing we notice is the navigation on the page handled by a GET parameter `op`, eg ` ` We get access to a webpage where we can upload icons (max 32x32) or even draw an icon with built-in editor. # Pixelshop (Web, 300 points, 15 solves)Įveryone loves pixel art, and thanks to PixelShop you can now create pixel art from your browser! Exciting!
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