policy.xml

<policymap>
  <policy domain="coder" rights="none" pattern="EPHEMERAL" />
  <policy domain="coder" rights="none" pattern="URL" />
  <policy domain="coder" rights="none" pattern="HTTPS" />
  <policy domain="coder" rights="none" pattern="MVG" />
  <policy domain="coder" rights="none" pattern="MSL" />
</policymap>

Command convert -list policy will show you where you should put the file above. Also use it to verify your inputs:

$ convert -list policy

Path: /etc/ImageMagick-6/policy.xml
  Policy: undefined
    rights: None 
  Policy: Coder
    rights: None 
    pattern: EPHEMERAL
  Policy: Coder
    rights: None 
    pattern: URL
  Policy: Coder
    rights: None 
    pattern: HTTPS
  Policy: Coder
    rights: None 
    pattern: MVG
  Policy: Coder
    rights: None 
    pattern: MSL

Path: [built-in]
  Policy: Undefined
    rights: None 

Awesome, Web app coders should also investigate sandboxing ImageMagick to limit its access.