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

Combining a lot of this Regex into one, that will allow for spaces where allowed and multi-level url encoding:

(?i)(%(25){0,}20|\s)(%(25){0,}24|$)(%(25){0,}20|\s)(%(25){0,}7B|{){0,1}(%(25){0,}20|\s)(%(25){0,}(6A|4A)|J)(%(25){0,}(6E|4E)|N)(%(25){0,}(64|44)|D)(%(25){0,}(69|49)|I)(%(25){0,}20|\s)(%(25){0,}3A|:)[\w%]+(%(25){1,}3A|:)(%(25){1,}2F|/)[^\n]+

Breakdown:
(?i) = case-insensitive
(%(25){0,}20|\s)* = any number of spaces
(%(25){0,}24|$) = $
(%(25){0,}20|\s)*
(%(25){0,}7B|{){0,1} = { zero or one time Updated condition
(%(25){0,}20|\s)
(%(25){0,}(6A|4A)|J) = J
(%(25){0,}(6E|4E)|N) = N
(%(25){0,}(64|44)|D) = D
(%(25){0,}(69|49)|I) =I
(%(25){0,}20|\s)*
(%(25){0,}3A|:) = :
[\w%]+ = any number of any letters, url encoded or not
(%(25){0,}3A|:)
(%(25){0,}2F|/) = /
[^\n]+ = until end of line

Examples that should work:
$ { JNDI : ANYPROTOCOL:/
${jndi:ldap:/
${jNDi:l%252564ap:/

RegEx101 breakdown: https://regex101.com/r/RGuaM9/1/

Edit: I realize that the first { is not absolutely required. Therefore, I have made that optional now, by adding {0,1} to the end of it.

Also, we have captured several very different methods of attempting this exploit in our environment, which involve more programmatic attempts to obscure the exploit, using methods like $upper/$lower, among others. You can see them captured in an alternate version of the Regex below:

https://regex101.com/r/jjCEHO/1

The EDR tool I'm using has a length limitation for conditions, so I had to create a separate Regex to capture these very different methods. I recommend you check for both Regex patterns:

(?i)$((::-[A-Z%]}$){1,}|(ENV|LOWER|UPPER):).+[:}]{2}/[^\n]+

Note: I did not convert this second method into URLEncoded strings, but feel free to do so, if you believe it beneficial.

Here is the combined Regex for both sets of conditions, together:

(?i)((%(25){0,}20|\s)(%(25){0,}24|$)(%(25){0,}20|\s)(%(25){0,}7B|{){0,1}(%(25){0,}20|\s)(%(25){0,}(6A|4A)|J)(%(25){0,}(6E|4E)|N)(%(25){0,}(64|44)|D)(%(25){0,}(69|49)|I)(%(25){0,}20|\s)(%(25){0,}3A|:)[\w%]+(%(25){1,}3A|:)(%(25){1,}2F|/)|$((::-[A-Z%]}$){1,}|(ENV|LOWER|UPPER):).+[:}]{2}/)[^\n]+

This might be helpful, basically gets all fixed disks on Windows and performs the one liner provided above to look for vulnerable jar files

Should work on Server 2008 -> 2022, hopefully it's helpful.

<# 
.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
.EXAMPLE 
    .\check_CVE-2021-44228.ps1
.NOTES 
    Created by Eric Schewe 2021-12-13
#> 

# 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 -ErrorAction SilentlyContinue | ForEach-Object {Select-String "JndiLookup.class" $_} | Select-Object -ExpandProperty Path

    }
    # 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 -ErrorAction SilentlyContinue | ForEach-Object {Select-String "JndiLookup.class" $_} | Select-Object -ExpandProperty Path

    }

}

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

@carloswpa Thanks! Unfortunately this breaks the script. I get the following error:

At C:\Users\Administrator\Desktop\Log4jSCAN\Windows\log4jscanV2.ps1:4 char:54

• gci 'C:' -rec -force -include *.jar -ea 0 | where {!$.PSIsContainer} | foreach ...

•                                                  ~
  

Missing expression after unary operator '!'.
At C:\Users\Administrator\Desktop\Log4jSCAN\Windows\log4jscanV2.ps1:4 char:54

• gci 'C:' -rec -force -include *.jar -ea 0 | where {!$.PSIsContainer} | foreach ...

•                                                  ~~~~~~~~~~~~~~~
  

Unexpected token '$.PSIsContainer' in expression or statement.
At C:\Users\Administrator\Desktop\Log4jSCAN\Windows\log4jscanV2.ps1:5 char:54

• gci 'D:' -rec -force -include *.jar -ea 0 | where {!$.PSIsContainer} | foreach ...

•                                                  ~
  

Missing expression after unary operator '!'.
At C:\Users\Administrator\Desktop\Log4jSCAN\Windows\log4jscanV2.ps1:5 char:54

• gci 'D:' -rec -force -include *.jar -ea 0 | where {!$.PSIsContainer} | foreach ...

•                                                  ~~~~~~~~~~~~~~~
  

Unexpected token '$.PSIsContainer' in expression or statement.
At C:\Users\Administrator\Desktop\Log4jSCAN\Windows\log4jscanV2.ps1:6 char:54

• gci 'E:' -rec -force -include *.jar -ea 0 | where {!$.PSIsContainer} | foreach ...

•                                                  ~
  

Missing expression after unary operator '!'.
At C:\Users\Administrator\Desktop\Log4jSCAN\Windows\log4jscanV2.ps1:6 char:54

• gci 'E:' -rec -force -include *.jar -ea 0 | where {!$.PSIsContainer} | foreach ...

•                                                  ~~~~~~~~~~~~~~~
  

Unexpected token '$.PSIsContainer' in expression or statement.
+ CategoryInfo : ParserError: (:) [], ParentContainsErrorRecordException
+ FullyQualifiedErrorId : MissingExpressionAfterOperator

@TheFiZi i made some modifications, hoping this helps

<# 
.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 - Replace attribute -Include by -Filter (prevent unauthorized access exception stopping scan)
        1.4 - Take only disks with a drive letter
        1.5 - Remove duplicate path with Get-Unique cmdlet
        1.6 - TODO : Out-File
.EXAMPLE 
    .\check_CVE-2021-44228.ps1
.NOTES 
    Created by Eric SCHEWE 2021-12-13
    Modified by Cedric BARBOTIN 2021-12-14
#> 

# Get machine name
$machine = Invoke-Expression -Command 'hostname'

# 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" }
}
# Take only disk with a drive letter
$disks = $disks | Where-Object { -not [string]::IsNullOrWhitespace($_.DriveLetter) }

# 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 -Filter *.jar -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 -Filter *.jar -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"

Found on :

• OWASP Zed Attack Proxy
• Talend Open Studio (install and workspace directories)

I created a configuration Item script to be use within SCCM to detect devices where the .jar files has the lib that can be compromised that may help the hunters out there.

Cred to @TheFiZi

.Synopsis 
    Script for CI detection of CVE-2021-44228 with SCCM

.DESCRIPTION 
    Cred: https://gist.github.com/Neo23x0/e4c8b03ff8cdf1fa63b7d15db6e3860b#find-vulnerable-software-windows
          Eric Schewe 2021-12-13

.NOTES 
    1.0 2021-12-14 Created by Daniel Olsson 
    1.1 2021-12-15 Added exclusion for junction / reparse 
#> 

$disks = Get-Volume | Where-Object {$_.DriveType -eq "Fixed" -and $_.DriveLetter -ne $null}
$discoveryFlag = $false
$response = $false

foreach ($disk in $disks) {
    $response = Get-ChildItem -Path "$($disk.DriveLetter):\" -File "*.jar" -Recurse -Attributes !reparsepoint -ErrorAction SilentlyContinue | ForEach-Object {Select-String "JndiLookup.class" $_} | Select-Object -ExpandProperty Path
    if($response){
        $discoveryFlag = $true
    }
    #$response
}
if($discoveryFlag){
    return $true
}
else{
    Return $false
}`

On macOS the search for Obfuscated Variants fails, cause it uses characters macOS-shell won't support.
I modified like this, can someone confirm this is correct?
sudo find /var/log/ -type f -exec sh -c "cat {} | LC_CTYPE=C sed -e 's/\${lower://'g | LC_CTYPE=C tr -d '}' | egrep -I -i 'jndi:(ldap[s]?|rmi|dns|nis|iiop|corba|nds|http):'" \;

For Windows Servers and Computers, a simple command to get all the jar files with "jndilookup.class":
for /r %f in (*.jar) do (find /i /c "JndiLookup.class" "%f" 1>nul && echo "%f" >> "c:\lista.txt")

If you have root access to a box containing docker images, based on @umitgunduz 's comment, you can use the following script to iterate through all docker containers, and find usages of JndiLookup.class:

for container in `docker ps -q`; do
# show the name of the container
docker inspect --format='{{.Name}}' $container;
 # find instances of JndiLookup.class in files matching with log4*.jar
docker exec -u root $container find -name "log4*.jar" -exec sh -c 'unzip -l "{}" | grep -i --color=always JndiLookup.class' \; -print
done

Required help please for Solaris 10, getting below

bash-3.2# egrep -I -i -r '$({|%7B)jndi:(ldap[s]?|rmi|dns|nis|iiop|corba|nds|http):/[^\n]+' /var/log
egrep: illegal option -- I
egrep: illegal option -- r
usage: egrep [ -bchilnsv ] [ -e exp ] [ -f file ] [ strings ] [ file ] ...
bash-3.2# find /var/log -name *.gz -print0 | xargs -0 zgrep -E -i '$({|%7B)jndi:(ldap[s]?|rmi|dns|nis|iiop|corba|nds|http):/[^\n]+' find: bad option -print0
find: [-H | -L] path-list predicate-list
xargs: illegal option -- 0
xargs: Usage: xargs: [-t] [-p] [-e[eofstr]] [-E eofstr] [-I replstr] [-i[replstr]] [-L #] [-l[#]] [-n # [-x]] [-s size] [cmd [args ...]]

Here's one I've been working on. So far detects all variations I've seen,even urlencoded. Just make sure to use case-insensitive for grep, or /i for everythign else.

https://gist.github.com/carlchan/916ed5edbef7c8d1c00be67daae8933e

(\$|%(25)*24)(\{|%(25)*7B)(((\$|%(25)*24)(\{|%(25)*7B)[^}]+(j|%[46]a)(n|%[46]e)?(d|%[46]4)?(i|%[46]9)?(%(25)*7(d|%[46]4)|\})|(j|%[46]a)(n|%[46]e)?(d|%[46]4)?(i|%[46]9)?)((\$|%(25)*24)(\{|%(25)*7B)[^}]+(j|%[46]a)?(n|%[46]e)(d|%[46]4)?(i|%[46]9)?(%(25)*7(d|%[46]4)|\})|(j|%[46]a)?(n|%[46]e)(d|%[46]4)?(i|%[46]9)?)((\$|%(25)*24)(\{|%(25)*7B)[^}]+(j|%[46]a)?(n|%[46]e)?(d|%[46]4)(i|%[46]9)?(%(25)*7(d|%[46]4)|\})|(j|%[46]a)?(n|%[46]e)?(d|%[46]4)(i|%[46]9)?)((\$|%(25)*24)(\{|%(25)*7B)[^}]+(j|%[46]a)?(n|%[46]e)?(d|%[46]4)?(i|%[46]9)(%(25)*7(d|%[46]4)|\})|(j|%[46]a)?(n|%[46]e)?(d|%[46]4)?(i|%[46]9))|((\$|%(25)*24)(\{|%(25)*7B)[^}]+(j|%[46]a)?(n|%[46]e)?(d|%[46]4)?(i|%[46]9)?(%(25)*7(d|%[46]4)|\})|(j|%[46]a|n|%[46]e|d|%[46]4|i|%[46]9)+)+)

In our server there are ZERO software using log4j
We detected a LOT of attempt but how to understand if an attack succeded?

@realtebo I guess if you have zero software using log4j then it is not possible for an attack to succeed right?

@alevenelli This is great, can you share some windows or powershall command to delete "JndiLookup.class" file. Thanks much

For Windows Servers and Computers, a simple command to get all the jar files with "jndilookup.class":
for /r %f in (*.jar) do (find /i /c "JndiLookup.class" "%f" 1>nul && echo "%f" >> "c:\lista.txt")

Fantastic resource here. Thanks!

I've put together a free (GPLv3) log4j detector for scanning the file-system. Handy for figuring out exactly what versions are lurking in the folders. Looks for String literals embedded inside the *.class files to determine Log4J version information (not based on hashes at all).

https://github.com/mergebase/log4j-detector

Sample output:

java -jar log4j-detector-2021.12.15.jar ./samples 

/opt/mergebase/log4j-detector/samples/log4j-1.2.17.jar contains Log4J-1.x   <= 1.2.17 _OLD_ :-|
/opt/mergebase/log4j-detector/samples/log4j-core-2.0-beta2.jar contains Log4J-2.x   <= 2.0-beta8 _POTENTIALLY_SAFE_ :-| (or did you already remove JndiLookup.class?) 
/opt/mergebase/log4j-detector/samples/log4j-core-2.0-beta9.jar contains Log4J-2.x   >= 2.0-beta9 (< 2.10.0) _VULNERABLE_ :-(
/opt/mergebase/log4j-detector/samples/log4j-core-2.0.2.jar contains Log4J-2.x   >= 2.0-beta9 (< 2.10.0) _VULNERABLE_ :-(
/opt/mergebase/log4j-detector/samples/log4j-core-2.0.jar contains Log4J-2.x   >= 2.0-beta9 (< 2.10.0) _VULNERABLE_ :-(
/opt/mergebase/log4j-detector/samples/log4j-core-2.10.0.jar contains Log4J-2.x   >= 2.10.0 _VULNERABLE_ :-(
/opt/mergebase/log4j-detector/samples/log4j-core-2.12.2.jar contains Log4J-2.x   >= 2.12.2 _SAFE_ :-)
/opt/mergebase/log4j-detector/samples/log4j-core-2.14.1.jar contains Log4J-2.x   >= 2.10.0 _VULNERABLE_ :-(
/opt/mergebase/log4j-detector/samples/log4j-core-2.15.0.jar contains Log4J-2.x   >= 2.15.0 _OKAY_ :-|
/opt/mergebase/log4j-detector/samples/log4j-core-2.16.0.jar contains Log4J-2.x   >= 2.16.0 _SAFE_ :-)

Thank you for the information in this gist. It was really helpful!
Here is my attempt on detection. It is a little slower, but can be used to extract IoCs as it does the deobfuscation in the beginning:

sed -E -e 's/%24/\$/'g -e 's/%7B/{/'gi -e 's/%7D/\}/'gi -e 's/%3A/:/'gi -e 's/%2F/\//'gi http_requests.log | sed -E -e 's/\$\{(lower:|upper:|::-)//'g | tr -d '}' | egrep -I -i '\$\{jndi:'

Just add your regex to the end of the pipeline, e.g. for IP addresses:

sed -E -e 's/%24/\$/'g -e 's/%7B/{/'gi -e 's/%7D/\}/'gi -e 's/%3A/:/'gi -e 's/%2F/\//'gi http_requests.log | sed -E -e 's/\$\{(lower:|upper:|::-)//'g | tr -d '}' | egrep -I -i '\$\{jndi:' | egrep -o '([0-9]{1,3}\.){3}[0-9]{1,3}' | sort | uniq

Some more commands to detect log4j loaded in a running JVM (courtesy of Twitter @web_bn), using JDK utils jps and jcmd:

Linux
jps | grep -v " Jps$" | cut -f1 -d " " | xargs -I '{}' jcmd '{}' VM.class_hierarchy | grep logging.log4j

Windows powershell:
jps | select-string -notmatch "jps$" | foreach {jcmd $_.Line.split()[0] VM.class_hierarchy} | select-string "log4j"

@TheFiZi it might be beneficial to add support for .war (web application archive) files

for some reason -path and -file does not work together when having an array of file types (at least for me, anyway), so I'm running it like so - it's a bit crude but it seems to work for me:

foreach ($disk in $disks) {
    set-location "$($disk.DriveLetter):\"
    $response+= Get-ChildItem  -File "*.jar","*.war" -Recurse -Attributes !reparsepoint -ErrorAction SilentlyContinue | ForEach-Object {Select-String "JndiLookup.class" $_} | Select-Object -ExpandProperty Path
    if($response){
        $discoveryFlag = $true
    }
    #$response
}

is there a way to determine if attempts where successful?

Yes, besides typical signs of compromise you should also be able to detect outgoing and unexpected network connections from your affected servers at the time of attack. Especially if you filter for RMI, LDAP or TLS(ldaps) connections - unfortunately on arbitrary ports.

@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