Unless your router is a full-fledged Linux box with GNU Bash installed (unlikely), you should be safe. Most don't have the storage for a full-blown Linux distribution, thus rely on the more compact Busybox shell:
RC=0 stuartl@rikishi ~ $ env X="() { :;} ; echo busted" busybox sh -c "echo completed"
completed
Not vulnerable, at least my version isn't.
Biting the hand that feeds IT
