Log4j RCE CVE-2021-44228 Exploitation Detection

log4j_rce_detection.md

log4j RCE Exploitation Detection

You can use these commands and rules to search for exploitation attempts against log4j RCE vulnerability CVE-2021-44228

Grep / Zgrep

This command searches for exploitation attempts in uncompressed files in folder /var/log and all sub folders

sudo egrep -I -i -r '\$(\{|%7B)jndi:(ldap[s]?|rmi|dns|nis|iiop|corba|nds|http):/[^\n]+' /var/log

This command searches for exploitation attempts in compressed files in folder /var/log and all sub folders

sudo find /var/log -name \*.gz -print0 | xargs -0 zgrep -E -i '\$(\{|%7B)jndi:(ldap[s]?|rmi|dns|nis|iiop|corba|nds|http):/[^\n]+'

Grep / Zgrep - Obfuscated Variants

These commands cover even the obfuscated variants but lack the file name in a match.

This command searches for exploitation attempts in uncompressed files in folder /var/log and all sub folders

sudo find /var/log/ -type f -exec sh -c "cat {} | sed -e 's/\${lower://'g | tr -d '}' | egrep -I -i 'jndi:(ldap[s]?|rmi|dns|nis|iiop|corba|nds|http):'" \;

This command searches for exploitation attempts in compressed files in folder /var/log and all sub folders

sudo find /var/log/ -name '*.gz' -type f -exec sh -c "zcat {} | sed -e 's/\${lower://'g | tr -d '}' | egrep -i 'jndi:(ldap[s]?|rmi|dns|nis|iiop|corba|nds|http):'" \;

Log4Shell-Rex

A massive regex to cover even the most obfuscated variants: https://github.com/back2root/log4shell-rex

(?:\$|%(?:25)*24|\\(?:0024|0{0,2}44))(?:{|%(?:25)*7[Bb]|\\(?:007[Bb]|0{0,2}173)).{0,30}?((?:[Jj]|%(?:25)*[46][Aa]|\\(?:00[46][Aa]|0{0,2}1[15]2)).{0,30}?(?:[Nn]|%(?:25)*[46][Ee]|\\(?:00[46][Ee]|0{0,2}1[15]6)).{0,30}?(?:[Dd]|%(?:25)*[46]4|\\(?:00[46]4|0{0,2}1[04]4)).{0,30}?(?:[Ii]|%(?:25)*[46]9|\\(?:00[46]9|0{0,2}1[15]1)|ı).{0,30}?(?::|%(?:25)*3[Aa]|\\(?:003[Aa]|0{0,2}72)).{0,30}?((?:[Ll]|%(?:25)*[46][Cc]|\\(?:00[46][Cc]|0{0,2}1[15]4)).{0,30}?(?:[Dd]|%(?:25)*[46]4|\\(?:00[46]4|0{0,2}1[04]4)).{0,30}?(?:[Aa]|%(?:25)*[46]1|\\(?:00[46]1|0{0,2}1[04]1)).{0,30}?(?:[Pp]|%(?:25)*[57]0|\\(?:00[57]0|0{0,2}1[26]0))(?:.{0,30}?(?:[Ss]|%(?:25)*[57]3|\\(?:00[57]3|0{0,2}1[26]3)))?|(?:[Rr]|%(?:25)*[57]2|\\(?:00[57]2|0{0,2}1[26]2)).{0,30}?(?:[Mm]|%(?:25)*[46][Dd]|\\(?:00[46][Dd]|0{0,2}1[15]5)).{0,30}?(?:[Ii]|%(?:25)*[46]9|\\(?:00[46]9|0{0,2}1[15]1)|ı)|(?:[Dd]|%(?:25)*[46]4|\\(?:00[46]4|0{0,2}1[04]4)).{0,30}?(?:[Nn]|%(?:25)*[46][Ee]|\\(?:00[46][Ee]|0{0,2}1[15]6)).{0,30}?(?:[Ss]|%(?:25)*[57]3|\\(?:00[57]3|0{0,2}1[26]3))|(?:[Nn]|%(?:25)*[46][Ee]|\\(?:00[46][Ee]|0{0,2}1[15]6)).{0,30}?(?:[Ii]|%(?:25)*[46]9|\\(?:00[46]9|0{0,2}1[15]1)|ı).{0,30}?(?:[Ss]|%(?:25)*[57]3|\\(?:00[57]3|0{0,2}1[26]3))|(?:.{0,30}?(?:[Ii]|%(?:25)*[46]9|\\(?:00[46]9|0{0,2}1[15]1)|ı)){2}.{0,30}?(?:[Oo]|%(?:25)*[46][Ff]|\\(?:00[46][Ff]|0{0,2}1[15]7)).{0,30}?(?:[Pp]|%(?:25)*[57]0|\\(?:00[57]0|0{0,2}1[26]0))|(?:[Cc]|%(?:25)*[46]3|\\(?:00[46]3|0{0,2}1[04]3)).{0,30}?(?:[Oo]|%(?:25)*[46][Ff]|\\(?:00[46][Ff]|0{0,2}1[15]7)).{0,30}?(?:[Rr]|%(?:25)*[57]2|\\(?:00[57]2|0{0,2}1[26]2)).{0,30}?(?:[Bb]|%(?:25)*[46]2|\\(?:00[46]2|0{0,2}1[04]2)).{0,30}?(?:[Aa]|%(?:25)*[46]1|\\(?:00[46]1|0{0,2}1[04]1))|(?:[Nn]|%(?:25)*[46][Ee]|\\(?:00[46][Ee]|0{0,2}1[15]6)).{0,30}?(?:[Dd]|%(?:25)*[46]4|\\(?:00[46]4|0{0,2}1[04]4)).{0,30}?(?:[Ss]|%(?:25)*[57]3|\\(?:00[57]3|0{0,2}1[26]3))|(?:[Hh]|%(?:25)*[46]8|\\(?:00[46]8|0{0,2}1[15]0))(?:.{0,30}?(?:[Tt]|%(?:25)*[57]4|\\(?:00[57]4|0{0,2}1[26]4))){2}.{0,30}?(?:[Pp]|%(?:25)*[57]0|\\(?:00[57]0|0{0,2}1[26]0))(?:.{0,30}?(?:[Ss]|%(?:25)*[57]3|\\(?:00[57]3|0{0,2}1[26]3)))?).{0,30}?(?::|%(?:25)*3[Aa]|\\(?:003[Aa]|0{0,2}72)).{0,30}?(?:\/|%(?:25)*2[Ff]|\\(?:002[Ff]|0{0,2}57)|\${)|(?:[Bb]|%(?:25)*[46]2|\\(?:00[46]2|0{0,2}1[04]2)).{0,30}?(?:[Aa]|%(?:25)*[46]1|\\(?:00[46]1|0{0,2}1[04]1)).{0,30}?(?:[Ss]|%(?:25)*[57]3|\\(?:00[57]3|0{0,2}1[26]3)).{0,30}?(?:[Ee]|%(?:25)*[46]5|\\(?:00[46]5|0{0,2}1[04]5)).{2,60}?(?::|%(?:25)*3[Aa]|\\(?:003[Aa]|0{0,2}72))(JH[s-v]|[\x2b\x2f-9A-Za-z][CSiy]R7|[\x2b\x2f-9A-Za-z]{2}[048AEIMQUYcgkosw]ke[\x2b\x2f-9w-z]))

Log4Shell Detector (Python)

Python based scanner to detect the most obfuscated forms of the exploit codes.

https://github.com/Neo23x0/log4shell-detector

Find Log4j on Linux

ps aux | egrep '[l]og4j'
find / -iname "log4j*"
lsof | grep log4j
grep -r --include *.[wj]ar "JndiLookup.class" / 2>&1 | grep matches

Find Vulnerable Log4j on Windows

gci 'C:\' -rec -force -include *.jar -ea 0 | foreach {select-string "JndiLookup.class" $_} | select -exp Path

by @CyberRaiju

YARA

https://github.com/Neo23x0/signature-base/blob/master/yara/expl_log4j_cve_2021_44228.yar

Help

Please report findings that are not covered by these detection attempts.

Credits

I got help and ideas from

• @matthias_kaiser
• @daphiel
• @Reelix
• @atom-b

@djblazkowicz Thank you! Now I have to re-audit everything for .war file :(

I took your idea and did this instead so I could change as little as possible:

Get-ChildItem "$($disk.DriveLetter):\" -Recurse -Force -Include @("*.jar","*.war") -ErrorAction SilentlyContinue | ForEach-Object { Select-String "JndiLookup.class" $_ } | Select-Object -ExpandProperty Path | Get-Unique

Complete updated script:

<# 
.Synopsis 
    Checks the local system for Log4Shell Vulnerability [CVE-2021-44228]
.DESCRIPTION 
    Gets a list of all volumes on the server, loops through searching each disk for Log4j stuff
    Using base search from https://gist.github.com/Neo23x0/e4c8b03ff8cdf1fa63b7d15db6e3860b#find-vulnerable-software-windows

    Version History
        1.0 - Initial release
        1.1 - Changed ErrorAction to "Continue" instead of stopping the script
        1.2 - Went back to SilentlyContinue, so much noise
        1.3 - Borrowed some improvements from @cedric2bx (https://gist.github.com/Neo23x0/e4c8b03ff8cdf1fa63b7d15db6e3860b#gistcomment-3995092)
                Replace attribute -Include by -Filter (prevent unauthorized access exception stopping scan)
                Remove duplicate path with Get-Unique cmdlet
        1.4 - Added .war support thanks to @djblazkowicz (https://gist.github.com/Neo23x0/e4c8b03ff8cdf1fa63b7d15db6e3860b#gistcomment-3998189)
.EXAMPLE 
    .\check_CVE-2021-44228.ps1
.NOTES 
    Created by Eric Schewe 2021-12-13
    Modified by Cedric BARBOTIN 2021-12-14
#> 

# Get Windows Version string
$windowsVersion = (Get-WmiObject -class Win32_OperatingSystem).Caption

# Server 2008 (R2)
if ($windowsVersion -like "*2008*") {

    $disks = [System.IO.DriveInfo]::getdrives() | Where-Object {$_.DriveType -eq "Fixed"}

}
# Everything else
else {

    $disks = Get-Volume | Where-Object {$_.DriveType -eq "Fixed"}

}

# I have no idea why I had to write it this way and why .Count didn't just work
$diskCount = $disks | Measure-Object | Select-Object Count -ExpandProperty Count

Write-Host -ForegroundColor Green "$(Get-Date -Format "yyyy-MM-dd H:mm:ss") - Starting the search of $($diskCount) disks"

foreach ($disk in $disks) {

    # One liner from https://gist.github.com/Neo23x0/e4c8b03ff8cdf1fa63b7d15db6e3860b#find-vulnerable-software-windows
    # gci 'C:\' -rec -force -include *.jar -ea 0 | foreach {select-string "JndiLookup.class" $_} | select -exp Path

    # Server 2008 (R2)
    if ($windowsVersion -like "*2008*") {

        Write-Host -ForegroundColor Yellow "  $(Get-Date -Format "yyyy-MM-dd H:mm:ss") - Checking $($disk.Name): - $($disk.VolumeLabel)"
        Get-ChildItem "$($disk.Name)" -Recurse -Force -Include @("*.jar","*.war") -ErrorAction SilentlyContinue | ForEach-Object { Select-String "JndiLookup.class" $_ } | Select-Object -ExpandProperty Path | Get-Unique

    }
    # Everything else
    else {

        Write-Host -ForegroundColor Yellow "  $(Get-Date -Format "yyyy-MM-dd H:mm:ss") - Checking $($disk.DriveLetter): - $($disk.VolumeLabel)"
        Get-ChildItem "$($disk.DriveLetter):\" -Recurse -Force -Include @("*.jar","*.war") -ErrorAction SilentlyContinue | ForEach-Object { Select-String "JndiLookup.class" $_ } | Select-Object -ExpandProperty Path | Get-Unique

    }

}

Write-Host -ForegroundColor Green "$(Get-Date -Format "yyyy-MM-dd H:mm:ss") - Done checking all drives"

Thanks for the script @TheFiZi