From djb@cr.yp.to Wed Dec 15 14:21:02 2004 Date: 15 Dec 2004 08:16:36 -0000 From: D. J. Bernstein To: securesoftware@list.cr.yp.to, filter@bolthole.com Subject: [remote] [control] elm/bolthole filter 2.6.1 save_embedded_address overflows address buffer Ariel Berkman, a student in my Fall 2004 UNIX Security Holes course, has discovered a remotely exploitable security hole in the elm/bolthole filter program. I'm publishing this notice, but all the discovery credits should be assigned to Berkman. You are at risk if you feed incoming email through the filter program. Anyone sending you email can take complete control over your account: he can read and modify your files, watch the programs you're running, etc. Proof of concept: On an x86 computer running FreeBSD 4.10, type wget http://www.bolthole.com/filter/filter2.6.1.tar.gz gunzip < filter2.6.1.tar.gz | tar -xf - cd filter2.6.1 env TOUCH=/usr/bin/touch make to download and compile the filter program, version 2.6.1 (current). Then save the file 11.mail attached to this message, and type ./filter < 11.mail with the unauthorized result that a file named x is removed from the current directory. (I tested this with a 534-byte environment, as reported by printenv | wc -c.) Here's the bug: In filter.c, save_embedded_address() copies any amount of data into an address[LONG_STRING] array. ---D. J. Bernstein, Associate Professor, Department of Mathematics, Statistics, and Computer Science, University of Illinois at Chicago [ Part 2, Text/PLAIN (charset: unknown-8bit) 12 lines. ] [ Unable to print this part. ]