zoo decoder 2.10 (zoo-2.10), as used in multiple products including (1) Barracuda Spam Firewall 3.4 and later with virusdef before 2.0.6399, (2) Spam Firewall before 3.4 20070319 with virusdef before 2.0.6399o, and (3) AMaViS 2.4.1 and earlier, allows remote attackers to cause a denial of service (infinite loop) via a ZOO archive with a direntry structure that points to a previous file.