didjvu and pdf2djvu are DjVu encoders that both use c44 (a command-line IW44 encoder, part of DjVuLibre) under the hood. More precisely, this is what they do: * create a unique temporary file directly in /tmp (or in $TMPDIR) * pass name of this file to c44 as the output file name Unfortunately, it turns out that c44 deletes the output file, and then creates a new one under the same name (without O_EXCL). This opens a race window, during which malicious user could their own file under this name. The bugs were fixed in didjvu 0.4 and pdf2djvu 0.7.21. References: https://bitbucket.org/jwilk/didjvu/issue/8 https://bitbucket.org/jwilk/pdf2djvu/issue/103 http://sourceforge.net/p/djvu/djvulibre-git/ci/release.3.5.27.1/tree/tools/c44.cpp#l769 -- Jakub Wilk