趁火打劫

chènhuǒdǎjié
  1. lit. to loot a burning house (idiom)
  2. fig. to take advantage of sb's misfortune

CEDICT

to take advantage of chaos for one's own profit

Wiktionary

趁人之危，从中取利。《黄绣球．第三回》：「这一天见来的很是不少，黄通理更代为踌躇，怕的是越来越多，容不下去。而且难免有趁火打劫，顺手牵羊的事。」也作「趁火抢劫」、「趁鬨打劫」。

重編國語辭典

  1. 敌方遇到困境、麻烦时，便乘此机会进兵出击，从而制服对手
  2. 趁人遭遇危难，大捞便宜

維基詞典

Entry Composition

=1 趁 chèn
  1. to avail oneself of
  2. to take advantage of
=1 趁 chèn old variant of 趁 chèn
2 火 huǒ
  1. fire
  2. urgent
  3. ammunition
  4. fiery or flaming
  5. internal heat (Chinese medicine)
  6. hot (popular)
  7. classifier for military units (old)
  8. Kangxi radical 86
3 打劫 dǎjié
  1. to loot
  2. to rob
  3. to plunder
  4. to ransack