[Esd-l] ALERT: Another ZIP trick is out...

John D. Hardin jhardin at impsec.org
Wed Mar 17 20:39:15 PST 2004


Apparently there's a way to obfuscate filenames in ZIP files. I need
to look into it in some more detail, but the symptom is the ZIP index
(unzip -l and unzip -v) reports a different filename than is actually

I've added a "decryption" scan to the development sanitizer. Note that
this DOES NOT actually decrypt the ZIP file; running "unzip -t" on it
with a bogus password is apparently sufficient to reveal the
obfuscated filename.

You need to have a version of unzip that supports the -P (password)  
argument. 5.50 and later work, 5.40 and below do not. I'm checking
5.41 and 5.42 right now.

Workaround: for the worm I've seen, add "*.ePK" to your zipfile poison
list. This may not work on variants. "*.?PK" may be better, at the
risk of more false positives.

Stay tuned.

 John Hardin KA7OHZ    ICQ#15735746    http://www.impsec.org/~jhardin/
 jhardin at impsec.org    FALaholic #11174    pgpk -a jhardin at impsec.org
 key: 0xB8732E79 - 2D8C 34F4 6411 F507 136C  AF76 D822 E6E6 B873 2E79
  "Bother," said Pooh as he struggled with /etc/sendmail.cf, "it never
  does quite what I want. I wish Christopher Robin was here."
				-- Peter da Silva in a.s.r
   17 days until the Slovakian Presidential Election

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