From djb@cr.yp.to Wed Dec 15 14:21:33 2004 Date: 15 Dec 2004 08:20:11 -0000 From: D. J. Bernstein To: securesoftware@list.cr.yp.to, cups@easysw.com Subject: [remote] [control] CUPS 1.1.22 hpgltops ParseCommand overflows buf Ariel Berkman, a student in my Fall 2004 UNIX Security Holes course, has discovered a remotely exploitable security hole in CUPS. I'm publishing this notice, but all the discovery credits should be assigned to Berkman. A CUPS installation is at risk whenever it prints an HPGL file obtained from email (or a web page or any other source that could be controlled by an attacker). You are at risk if you print data through a CUPS installation at risk. The source of the HPGL file has complete control over the CUPS ``lp'' account; in particular, he can read and modify the files you are printing. Proof of concept: On an x86 computer running FreeBSD 4.10, as root, type cd /usr/ports/print/cups make install to download and compile the CUPS package, version 1.1.22 (current). Then, as any user, save the file 21.hpgl.gz attached to this message, and type gunzip 21.hpgl /usr/local/libexec/cups/filter/hpgltops \ 15 $USER test-title 1 none 21.hpgl > 21.ps with the unauthorized result that a file named x is removed from the current directory. (I tested this with a 541-byte environment, as reported by printenv | wc -c.) Here's the bug: In hpgl-input.c, ParseCommand() reads any number of bytes into a 262144-byte buf[] array. ---D. J. Bernstein, Associate Professor, Department of Mathematics, Statistics, and Computer Science, University of Illinois at Chicago [ Part 2, Application/X-GUNZIP 692bytes. ] [ Unable to print this part. ]