From djb@cr.yp.to Wed Dec 15 14:23:14 2004
Date: 15 Dec 2004 08:32:19 -0000
From: D. J. Bernstein <djb@cr.yp.to>
To: securesoftware@list.cr.yp.to, pcal-interest@lists.sourceforge.net
Subject: [remote] [control] pcal 4.7.1 getline overflows tmpbuf;
    get_holiday overflows tmp

Danny Lungstrom, a student in my Fall 2004 UNIX Security Holes course,
has discovered two remotely exploitable security holes in pcal. I'm
publishing this notice, but all the discovery credits should be assigned
to Lungstrom.

You are at risk if you receive a calendar file through email (or a web
page or any other source that could be controlled by an attacker) and
feed that file through pcal. Whoever provides the calendar file then has
complete control over your account: he can read and modify your files,
watch the programs you're running, etc.

The pcal documentation does not tell users to avoid taking input from
the network. In fact, one can easily find web pages that supply calendar
files for public use.

Proof of concept: On an x86 computer running FreeBSD 4.10, as root, type

   cd /usr/ports/print/pcal
   make install

to download and compile the pcal program, version 4.7.1 (current). Then,
as any user, save the file 71-1.cal attached to this message, and type

   pcal -f 71-1.cal > 71-1.ps

with the unauthorized result that a file named ``exploited'' is created
in the current directory. The file 71-2.cal has the same effect but uses
another buffer overflow. (I tested these with a 525-byte environment, as
reported by printenv | wc -c.)

Here are the bugs: In pcalutil.c, getline() copies any amount of data
into a fixed-length tmpbuf array. In readfile.c, get_holiday() uses an
unprotected strcpy() to copy data into a fixed-length tmp array.

---D. J. Bernstein, Associate Professor, Department of Mathematics,
Statistics, and Computer Science, University of Illinois at Chicago

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