modsecurity rule to filter CVE-2021-44228/LogJam/Log4Shell [update]

December 10, 2021

As a fast workaround, a friend of mine made a modsecurity rule to filter CVE-2021-44228/LogJam/Log4Shell, which he allowed me to share with you.

SecRule \
  ARGS|REQUEST_HEADERS|REQUEST_URI|REQUEST_BODY|REQUEST_COOKIES|REQUEST_LINE|QUERY_STRING "jndi:ldap:" \
  "phase:1, \
  id:751001, \
  t:none, \
  deny, \
  status:403, \
  log, \
  auditlog, \
  msg:'Block: CVE-2021-44228 - deny pattern \"jndi:ldap:\"', \
  severity:'5', \
  rev:1, \
  tag:'no_ar'"


New improved version:

  
SecRule \
  ARGS|REQUEST_HEADERS|REQUEST_URI|REQUEST_BODY|REQUEST_COOKIES|REQUEST_LINE|QUERY_STRING "jndi:ldap:|jndi:dns:|jndi:rmi:|jndi:rni:|\${jndi:" \
  "phase:1, \
  id:751001, \
  t:none, \
  deny, \
  status:403, \
  log, \
  auditlog, \
  msg:'DVT: CVE-2021-44228 - phase 1 - deny known \"jndi:\" pattern', \
  severity:'5', \
  rev:1, \
  tag:'no_ar'"
  
SecRule \
  ARGS|REQUEST_HEADERS|REQUEST_URI|REQUEST_BODY|REQUEST_COOKIES|REQUEST_LINE|QUERY_STRING "jndi:ldap:|jndi:dns:|jndi:rmi:|jndi:rni:|\${jndi:" \
  "phase:2, \
  id:751002, \
  t:none, \
  deny, \
  status:403, \
  log, \
  auditlog, \
  msg:'DVT: CVE-2021-44228 - phase 2 - deny known \"jndi:\" pattern', \
  severity:'5', \
  rev:1, \
  tag:'no_ar'


Jitsi Workaround for CVE-2021-44228/LogJam/Log4Shell

You surely heard of the LogJam / Log4Shell / CVE-2021-44228 – if not, take a look at this blog post. If you’re running Jitsi is most likely vulnerable and as there is no fix currently, you need a workaround which I provide here for you. You need to add -Dlog4j2.formatMsgNoLookups=True at the correct places in the file – the position is important.

/etc/jitsi/jicofo/config

/etc/jitsi/videobridge/config

And restart the processes or restart the server.