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Log4Shell-Rex\n\nThe following RegEx was written in an attempt to match indicators of a Log4Shell (CVE-2021-44228 and\nCVE-2021-45046) exploitation.\n\n**If you run a version from pre 2021/12/21, it's highly recommended to test and update.**\\\nI've removed some quirks and enhanced performance.\n\nThe Regex aims being PCRE compatible, but should also run on re2 and potentially more RegEx engines.\n\n**RegEx:**\n```regex\n(?im)(?:^|[\\n]).*?(?:[\\x24]|%(?:25%?)*24|\\\\u?0*(?:44|24))(?:[\\x7b]|%(?:25%?)*7b|\\\\u?0*(?:7b|173))[^\\n]*?((?:j|%(?:25%?)*(?:4a|6a)|\\\\u?0*(?:112|6a|4a|152))[^\\n]*?(?:n|%(?:25%?)*(?:4e|6e)|\\\\u?0*(?:4e|156|116|6e))[^\\n]*?(?:d|%(?:25%?)*(?:44|64)|\\\\u?0*(?:44|144|104|64))[^\\n]*?(?:[i\\x{130}\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\u?0*(?:111|69|49|151|130|460|131|461))[^\\n]*?(?:[\\x3a]|%(?:25%?)*3a|\\\\u?0*(?:72|3a))[^\\n]*?((?:l|%(?:25%?)*(?:4c|6c)|\\\\u?0*(?:154|114|6c|4c))[^\\n]*?(?:d|%(?:25%?)*(?:44|64)|\\\\u?0*(?:44|144|104|64))[^\\n]*?(?:a|%(?:25%?)*(?:41|61)|\\\\u?0*(?:101|61|41|141))[^\\n]*?(?:p|%(?:25%?)*(?:50|70)|\\\\u?0*(?:70|50|160|120))(?:[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163)))?|(?:r|%(?:25%?)*(?:52|72)|\\\\u?0*(?:122|72|52|162))[^\\n]*?(?:m|%(?:25%?)*(?:4d|6d)|\\\\u?0*(?:4d|155|115|6d))[^\\n]*?(?:[i\\x{130}\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\u?0*(?:111|69|49|151|130|460|131|461))|(?:d|%(?:25%?)*(?:44|64)|\\\\u?0*(?:44|144|104|64))[^\\n]*?(?:n|%(?:25%?)*(?:4e|6e)|\\\\u?0*(?:4e|156|116|6e))[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163))|(?:n|%(?:25%?)*(?:4e|6e)|\\\\u?0*(?:4e|156|116|6e))[^\\n]*?(?:[i\\x{130}\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\u?0*(?:111|69|49|151|130|460|131|461))[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163))|(?:[^\\n]*?(?:[i\\x{130}\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\u?0*(?:111|69|49|151|130|460|131|461))){2}[^\\n]*?(?:o|%(?:25%?)*(?:4f|6f)|\\\\u?0*(?:6f|4f|157|117))[^\\n]*?(?:p|%(?:25%?)*(?:50|70)|\\\\u?0*(?:70|50|160|120))|(?:c|%(?:25%?)*(?:43|63)|\\\\u?0*(?:143|103|63|43))[^\\n]*?(?:o|%(?:25%?)*(?:4f|6f)|\\\\u?0*(?:6f|4f|157|117))[^\\n]*?(?:r|%(?:25%?)*(?:52|72)|\\\\u?0*(?:122|72|52|162))[^\\n]*?(?:b|%(?:25%?)*(?:42|62)|\\\\u?0*(?:102|62|42|142))[^\\n]*?(?:a|%(?:25%?)*(?:41|61)|\\\\u?0*(?:101|61|41|141))|(?:n|%(?:25%?)*(?:4e|6e)|\\\\u?0*(?:4e|156|116|6e))[^\\n]*?(?:d|%(?:25%?)*(?:44|64)|\\\\u?0*(?:44|144|104|64))[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163))|(?:h|%(?:25%?)*(?:48|68)|\\\\u?0*(?:110|68|48|150))(?:[^\\n]*?(?:t|%(?:25%?)*(?:54|74)|\\\\u?0*(?:124|74|54|164))){2}[^\\n]*?(?:p|%(?:25%?)*(?:50|70)|\\\\u?0*(?:70|50|160|120))(?:[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163)))?)[^\\n]*?(?:[\\x3a]|%(?:25%?)*3a|\\\\u?0*(?:72|3a))|(?:b|%(?:25%?)*(?:42|62)|\\\\u?0*(?:102|62|42|142))[^\\n]*?(?:a|%(?:25%?)*(?:41|61)|\\\\u?0*(?:101|61|41|141))[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163))[^\\n]*?(?:e|%(?:25%?)*(?:45|65)|\\\\u?0*(?:45|145|105|65))[^\\n]*?(?:[\\x3a]|%(?:25%?)*3a|\\\\u?0*(?:72|3a))(JH[s-v]|[\\x2b\\x2f-9A-Za-z][CSiy]R7|[\\x2b\\x2f-9A-Za-z]{2}[048AEIMQUYcgkosw]ke[\\x2b\\x2f-9w-z]))\n```\n\n## Capabilities\n\nBy now, this regex should match the exploit, regardless:\n\n- Just logged\n- Case insensitive (also in all supported encodings)\n- URL Encoded\n- Recursively URL Encoded\n- With Unicode encoding\n- With Octal encoding\n- Base64 encoded (rudimentary)\n\n### Background\n\nThe goal is to have a RegEx that represents a reasonable tradeoff between detecting as many attack\nattempts as possible with an acceptable number of false positives.\n\nThe APT attacker will find a way around if necessary, but less elaborate attacks will leave the\nwarning light on.\n\nWhy a (single) RegEx: Because it can be easily executed on the CLI or in a SIEM without any\nadditional tools. If tools can be executed, do it, they exist.\n\nThe length of the regex is less of a problem than its performance. Despite the length, the RegEx\nshould be acceptably fast to execute on average log data.\n\n### Call for action\n\nI wanna make it hard to hide an attack in real world szenarios.\n\nIf this RegEx does not match sth. you have seen in the wild or can show being exploitable, please\ncreate an issue.\n\nIt is known, that you can work around the RegEx easily by encoding different parts of the attack\npattern using Base64. How ever, this is accepted, as `base64` did not finaly made it into an\nofficial Log4j release yet. ([LOG4J2-2446](https://issues.apache.org/jira/projects/LOG4J2/issues/LOG4J2-2446))\n\n### Tools\n\n- Test the RegEx: **[regex101](https://regex101.com/r/KqGG3W/24)**\n- Visualize the Regex: **[REGEXPER](https://regexper.com/#%28%3F%3A%5E%7C%5B%5Cn%5D%29.*%3F%28%3F%3A%5B%5Cx24%5D%7C%25%28%3F%3A25%25%3F%29*24%7C%5C%5Cu%3F0*%28%3F%3A44%7C24%29%29%28%3F%3A%5B%5Cx7b%5D%7C%25%28%3F%3A25%25%3F%29*7b%7C%5C%5Cu%3F0*%28%3F%3A7b%7C173%29%29%5B%5E%5Cn%5D*%3F%28%28%3F%3Aj%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A4a%7C6a%29%7C%5C%5Cu%3F0*%28%3F%3A112%7C6a%7C4a%7C152%29%29%5B%5E%5Cn%5D*%3F%28%3F%3An%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A4e%7C6e%29%7C%5C%5Cu%3F0*%28%3F%3A4e%7C156%7C116%7C6e%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Ad%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A44%7C64%29%7C%5C%5Cu%3F0*%28%3F%3A44%7C144%7C104%7C64%29%29%5B%5E%5Cn%5D*%3F%28%3F%3A%5Bi%5Cx%7B130%7D%5Cx%7B131%7D%5D%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A49%7C69%7CC4%25%28%3F%3A25%25%3F%29*B0%7CC4%25%28%3F%3A25%25%3F%29*B1%29%7C%5C%5Cu%3F0*%28%3F%3A111%7C69%7C49%7C151%7C130%7C460%7C131%7C461%29%29%5B%5E%5Cn%5D*%3F%28%3F%3A%5B%5Cx3a%5D%7C%25%28%3F%3A25%25%3F%29*3a%7C%5C%5Cu%3F0*%28%3F%3A72%7C3a%29%29%5B%5E%5Cn%5D*%3F%28%28%3F%3Al%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A4c%7C6c%29%7C%5C%5Cu%3F0*%28%3F%3A154%7C114%7C6c%7C4c%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Ad%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A44%7C64%29%7C%5C%5Cu%3F0*%28%3F%3A44%7C144%7C104%7C64%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Aa%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A41%7C61%29%7C%5C%5Cu%3F0*%28%3F%3A101%7C61%7C41%7C141%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Ap%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A50%7C70%29%7C%5C%5Cu%3F0*%28%3F%3A70%7C50%7C160%7C120%29%29%28%3F%3A%5B%5E%5Cn%5D*%3F%28%3F%3A%5Bs%5Cx%7B17f%7D%5D%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A53%7C73%7CC5%25%28%3F%3A25%25%3F%29*BF%29%7C%5C%5Cu%3F0*%28%3F%3A17f%7C123%7C577%7C73%7C53%7C163%29%29%29%3F%7C%28%3F%3Ar%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A52%7C72%29%7C%5C%5Cu%3F0*%28%3F%3A122%7C72%7C52%7C162%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Am%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A4d%7C6d%29%7C%5C%5Cu%3F0*%28%3F%3A4d%7C155%7C115%7C6d%29%29%5B%5E%5Cn%5D*%3F%28%3F%3A%5Bi%5Cx%7B130%7D%5Cx%7B131%7D%5D%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A49%7C69%7CC4%25%28%3F%3A25%25%3F%29*B0%7CC4%25%28%3F%3A25%25%3F%29*B1%29%7C%5C%5Cu%3F0*%28%3F%3A111%7C69%7C49%7C151%7C130%7C460%7C131%7C461%29%29%7C%28%3F%3Ad%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A44%7C64%29%7C%5C%5Cu%3F0*%28%3F%3A44%7C144%7C104%7C64%29%29%5B%5E%5Cn%5D*%3F%28%3F%3An%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A4e%7C6e%29%7C%5C%5Cu%3F0*%28%3F%3A4e%7C156%7C116%7C6e%29%29%5B%5E%5Cn%5D*%3F%28%3F%3A%5Bs%5Cx%7B17f%7D%5D%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A53%7C73%7CC5%25%28%3F%3A25%25%3F%29*BF%29%7C%5C%5Cu%3F0*%28%3F%3A17f%7C123%7C577%7C73%7C53%7C163%29%29%7C%28%3F%3An%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A4e%7C6e%29%7C%5C%5Cu%3F0*%28%3F%3A4e%7C156%7C116%7C6e%29%29%5B%5E%5Cn%5D*%3F%28%3F%3A%5Bi%5Cx%7B130%7D%5Cx%7B131%7D%5D%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A49%7C69%7CC4%25%28%3F%3A25%25%3F%29*B0%7CC4%25%28%3F%3A25%25%3F%29*B1%29%7C%5C%5Cu%3F0*%28%3F%3A111%7C69%7C49%7C151%7C130%7C460%7C131%7C461%29%29%5B%5E%5Cn%5D*%3F%28%3F%3A%5Bs%5Cx%7B17f%7D%5D%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A53%7C73%7CC5%25%28%3F%3A25%25%3F%29*BF%29%7C%5C%5Cu%3F0*%28%3F%3A17f%7C123%7C577%7C73%7C53%7C163%29%29%7C%28%3F%3A%5B%5E%5Cn%5D*%3F%28%3F%3A%5Bi%5Cx%7B130%7D%5Cx%7B131%7D%5D%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A49%7C69%7CC4%25%28%3F%3A25%25%3F%29*B0%7CC4%25%28%3F%3A25%25%3F%29*B1%29%7C%5C%5Cu%3F0*%28%3F%3A111%7C69%7C49%7C151%7C130%7C460%7C131%7C461%29%29%29%7B2%7D%5B%5E%5Cn%5D*%3F%28%3F%3Ao%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A4f%7C6f%29%7C%5C%5Cu%3F0*%28%3F%3A6f%7C4f%7C157%7C117%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Ap%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A50%7C70%29%7C%5C%5Cu%3F0*%28%3F%3A70%7C50%7C160%7C120%29%29%7C%28%3F%3Ac%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A43%7C63%29%7C%5C%5Cu%3F0*%28%3F%3A143%7C103%7C63%7C43%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Ao%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A4f%7C6f%29%7C%5C%5Cu%3F0*%28%3F%3A6f%7C4f%7C157%7C117%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Ar%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A52%7C72%29%7C%5C%5Cu%3F0*%28%3F%3A122%7C72%7C52%7C162%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Ab%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A42%7C62%29%7C%5C%5Cu%3F0*%28%3F%3A102%7C62%7C42%7C142%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Aa%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A41%7C61%29%7C%5C%5Cu%3F0*%28%3F%3A101%7C61%7C41%7C141%29%29%7C%28%3F%3An%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A4e%7C6e%29%7C%5C%5Cu%3F0*%28%3F%3A4e%7C156%7C116%7C6e%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Ad%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A44%7C64%29%7C%5C%5Cu%3F0*%28%3F%3A44%7C144%7C104%7C64%29%29%5B%5E%5Cn%5D*%3F%28%3F%3A%5Bs%5Cx%7B17f%7D%5D%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A53%7C73%7CC5%25%28%3F%3A25%25%3F%29*BF%29%7C%5C%5Cu%3F0*%28%3F%3A17f%7C123%7C577%7C73%7C53%7C163%29%29%7C%28%3F%3Ah%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A48%7C68%29%7C%5C%5Cu%3F0*%28%3F%3A110%7C68%7C48%7C150%29%29%28%3F%3A%5B%5E%5Cn%5D*%3F%28%3F%3At%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A54%7C74%29%7C%5C%5Cu%3F0*%28%3F%3A124%7C74%7C54%7C164%29%29%29%7B2%7D%5B%5E%5Cn%5D*%3F%28%3F%3Ap%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A50%7C70%29%7C%5C%5Cu%3F0*%28%3F%3A70%7C50%7C160%7C120%29%29%28%3F%3A%5B%5E%5Cn%5D*%3F%28%3F%3A%5Bs%5Cx%7B17f%7D%5D%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A53%7C73%7CC5%25%28%3F%3A25%25%3F%29*BF%29%7C%5C%5Cu%3F0*%28%3F%3A17f%7C123%7C577%7C73%7C53%7C163%29%29%29%3F%29%5B%5E%5Cn%5D*%3F%28%3F%3A%5B%5Cx3a%5D%7C%25%28%3F%3A25%25%3F%29*3a%7C%5C%5Cu%3F0*%28%3F%3A72%7C3a%29%29%7C%28%3F%3Ab%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A42%7C62%29%7C%5C%5Cu%3F0*%28%3F%3A102%7C62%7C42%7C142%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Aa%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A41%7C61%29%7C%5C%5Cu%3F0*%28%3F%3A101%7C61%7C41%7C141%29%29%5B%5E%5Cn%5D*%3F%28%3F%3A%5Bs%5Cx%7B17f%7D%5D%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A53%7C73%7CC5%25%28%3F%3A25%25%3F%29*BF%29%7C%5C%5Cu%3F0*%28%3F%3A17f%7C123%7C577%7C73%7C53%7C163%29%29%5B%5E%5Cn%5D*%3F%28%3F%3Ae%7C%25%28%3F%3A25%25%3F%29*%28%3F%3A45%7C65%29%7C%5C%5Cu%3F0*%28%3F%3A45%7C145%7C105%7C65%29%29%5B%5E%5Cn%5D*%3F%28%3F%3A%5B%5Cx3a%5D%7C%25%28%3F%3A25%25%3F%29*3a%7C%5C%5Cu%3F0*%28%3F%3A72%7C3a%29%29%28JH%5Bs-v%5D%7C%5B%5Cx2b%5Cx2f-9A-Za-z%5D%5BCSiy%5DR7%7C%5B%5Cx2b%5Cx2f-9A-Za-z%5D%7B2%7D%5B048AEIMQUYcgkosw%5Dke%5B%5Cx2b%5Cx2f-9w-z%5D%29%29)**\n\n## Hunting on your Linux machine\n\n### On the CLI with `grep`\n\n```bash\neval \"$(./RegEx_Generator.sh)\"\ngrep -P ${Log4ShellRex} \u003clogfile\u003e\n```\n\n```bash\ngrep -P '(?im)(?:^|[\\n]).*?(?:[\\x24]|%(?:25%?)*24|\\\\u?0*(?:44|24))(?:[\\x7b]|%(?:25%?)*7b|\\\\u?0*(?:7b|173))[^\\n]*?((?:j|%(?:25%?)*(?:4a|6a)|\\\\u?0*(?:112|6a|4a|152))[^\\n]*?(?:n|%(?:25%?)*(?:4e|6e)|\\\\u?0*(?:4e|156|116|6e))[^\\n]*?(?:d|%(?:25%?)*(?:44|64)|\\\\u?0*(?:44|144|104|64))[^\\n]*?(?:[i\\x{130}\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\u?0*(?:111|69|49|151|130|460|131|461))[^\\n]*?(?:[\\x3a]|%(?:25%?)*3a|\\\\u?0*(?:72|3a))[^\\n]*?((?:l|%(?:25%?)*(?:4c|6c)|\\\\u?0*(?:154|114|6c|4c))[^\\n]*?(?:d|%(?:25%?)*(?:44|64)|\\\\u?0*(?:44|144|104|64))[^\\n]*?(?:a|%(?:25%?)*(?:41|61)|\\\\u?0*(?:101|61|41|141))[^\\n]*?(?:p|%(?:25%?)*(?:50|70)|\\\\u?0*(?:70|50|160|120))(?:[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163)))?|(?:r|%(?:25%?)*(?:52|72)|\\\\u?0*(?:122|72|52|162))[^\\n]*?(?:m|%(?:25%?)*(?:4d|6d)|\\\\u?0*(?:4d|155|115|6d))[^\\n]*?(?:[i\\x{130}\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\u?0*(?:111|69|49|151|130|460|131|461))|(?:d|%(?:25%?)*(?:44|64)|\\\\u?0*(?:44|144|104|64))[^\\n]*?(?:n|%(?:25%?)*(?:4e|6e)|\\\\u?0*(?:4e|156|116|6e))[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163))|(?:n|%(?:25%?)*(?:4e|6e)|\\\\u?0*(?:4e|156|116|6e))[^\\n]*?(?:[i\\x{130}\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\u?0*(?:111|69|49|151|130|460|131|461))[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163))|(?:[^\\n]*?(?:[i\\x{130}\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\u?0*(?:111|69|49|151|130|460|131|461))){2}[^\\n]*?(?:o|%(?:25%?)*(?:4f|6f)|\\\\u?0*(?:6f|4f|157|117))[^\\n]*?(?:p|%(?:25%?)*(?:50|70)|\\\\u?0*(?:70|50|160|120))|(?:c|%(?:25%?)*(?:43|63)|\\\\u?0*(?:143|103|63|43))[^\\n]*?(?:o|%(?:25%?)*(?:4f|6f)|\\\\u?0*(?:6f|4f|157|117))[^\\n]*?(?:r|%(?:25%?)*(?:52|72)|\\\\u?0*(?:122|72|52|162))[^\\n]*?(?:b|%(?:25%?)*(?:42|62)|\\\\u?0*(?:102|62|42|142))[^\\n]*?(?:a|%(?:25%?)*(?:41|61)|\\\\u?0*(?:101|61|41|141))|(?:n|%(?:25%?)*(?:4e|6e)|\\\\u?0*(?:4e|156|116|6e))[^\\n]*?(?:d|%(?:25%?)*(?:44|64)|\\\\u?0*(?:44|144|104|64))[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163))|(?:h|%(?:25%?)*(?:48|68)|\\\\u?0*(?:110|68|48|150))(?:[^\\n]*?(?:t|%(?:25%?)*(?:54|74)|\\\\u?0*(?:124|74|54|164))){2}[^\\n]*?(?:p|%(?:25%?)*(?:50|70)|\\\\u?0*(?:70|50|160|120))(?:[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163)))?)[^\\n]*?(?:[\\x3a]|%(?:25%?)*3a|\\\\u?0*(?:72|3a))|(?:b|%(?:25%?)*(?:42|62)|\\\\u?0*(?:102|62|42|142))[^\\n]*?(?:a|%(?:25%?)*(?:41|61)|\\\\u?0*(?:101|61|41|141))[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163))[^\\n]*?(?:e|%(?:25%?)*(?:45|65)|\\\\u?0*(?:45|145|105|65))[^\\n]*?(?:[\\x3a]|%(?:25%?)*3a|\\\\u?0*(?:72|3a))(JH[s-v]|[\\x2b\\x2f-9A-Za-z][CSiy]R7|[\\x2b\\x2f-9A-Za-z]{2}[048AEIMQUYcgkosw]ke[\\x2b\\x2f-9w-z]))' \u003clogfile\u003e\n```\n\n### Combine it with `find` to recursively scan a (sub-)folder of log files\n\n```bash\neval \"$(./RegEx_Generator.sh)\"\nfind /var/log -name \"*.log\" | xargs grep -P ${Log4ShellRex}\n```\n\n```bash\nfind /var/log -name \"*.log\" | xargs grep -P '(?im)(?:^|[\\n]).*?(?:[\\x24]|%(?:25%?)*24|\\\\u?0*(?:44|24))(?:[\\x7b]|%(?:25%?)*7b|\\\\u?0*(?:7b|173))[^\\n]*?((?:j|%(?:25%?)*(?:4a|6a)|\\\\u?0*(?:112|6a|4a|152))[^\\n]*?(?:n|%(?:25%?)*(?:4e|6e)|\\\\u?0*(?:4e|156|116|6e))[^\\n]*?(?:d|%(?:25%?)*(?:44|64)|\\\\u?0*(?:44|144|104|64))[^\\n]*?(?:[i\\x{130}\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\u?0*(?:111|69|49|151|130|460|131|461))[^\\n]*?(?:[\\x3a]|%(?:25%?)*3a|\\\\u?0*(?:72|3a))[^\\n]*?((?:l|%(?:25%?)*(?:4c|6c)|\\\\u?0*(?:154|114|6c|4c))[^\\n]*?(?:d|%(?:25%?)*(?:44|64)|\\\\u?0*(?:44|144|104|64))[^\\n]*?(?:a|%(?:25%?)*(?:41|61)|\\\\u?0*(?:101|61|41|141))[^\\n]*?(?:p|%(?:25%?)*(?:50|70)|\\\\u?0*(?:70|50|160|120))(?:[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163)))?|(?:r|%(?:25%?)*(?:52|72)|\\\\u?0*(?:122|72|52|162))[^\\n]*?(?:m|%(?:25%?)*(?:4d|6d)|\\\\u?0*(?:4d|155|115|6d))[^\\n]*?(?:[i\\x{130}\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\u?0*(?:111|69|49|151|130|460|131|461))|(?:d|%(?:25%?)*(?:44|64)|\\\\u?0*(?:44|144|104|64))[^\\n]*?(?:n|%(?:25%?)*(?:4e|6e)|\\\\u?0*(?:4e|156|116|6e))[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163))|(?:n|%(?:25%?)*(?:4e|6e)|\\\\u?0*(?:4e|156|116|6e))[^\\n]*?(?:[i\\x{130}\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\u?0*(?:111|69|49|151|130|460|131|461))[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163))|(?:[^\\n]*?(?:[i\\x{130}\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\u?0*(?:111|69|49|151|130|460|131|461))){2}[^\\n]*?(?:o|%(?:25%?)*(?:4f|6f)|\\\\u?0*(?:6f|4f|157|117))[^\\n]*?(?:p|%(?:25%?)*(?:50|70)|\\\\u?0*(?:70|50|160|120))|(?:c|%(?:25%?)*(?:43|63)|\\\\u?0*(?:143|103|63|43))[^\\n]*?(?:o|%(?:25%?)*(?:4f|6f)|\\\\u?0*(?:6f|4f|157|117))[^\\n]*?(?:r|%(?:25%?)*(?:52|72)|\\\\u?0*(?:122|72|52|162))[^\\n]*?(?:b|%(?:25%?)*(?:42|62)|\\\\u?0*(?:102|62|42|142))[^\\n]*?(?:a|%(?:25%?)*(?:41|61)|\\\\u?0*(?:101|61|41|141))|(?:n|%(?:25%?)*(?:4e|6e)|\\\\u?0*(?:4e|156|116|6e))[^\\n]*?(?:d|%(?:25%?)*(?:44|64)|\\\\u?0*(?:44|144|104|64))[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163))|(?:h|%(?:25%?)*(?:48|68)|\\\\u?0*(?:110|68|48|150))(?:[^\\n]*?(?:t|%(?:25%?)*(?:54|74)|\\\\u?0*(?:124|74|54|164))){2}[^\\n]*?(?:p|%(?:25%?)*(?:50|70)|\\\\u?0*(?:70|50|160|120))(?:[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163)))?)[^\\n]*?(?:[\\x3a]|%(?:25%?)*3a|\\\\u?0*(?:72|3a))|(?:b|%(?:25%?)*(?:42|62)|\\\\u?0*(?:102|62|42|142))[^\\n]*?(?:a|%(?:25%?)*(?:41|61)|\\\\u?0*(?:101|61|41|141))[^\\n]*?(?:[s\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\u?0*(?:17f|123|577|73|53|163))[^\\n]*?(?:e|%(?:25%?)*(?:45|65)|\\\\u?0*(?:45|145|105|65))[^\\n]*?(?:[\\x3a]|%(?:25%?)*3a|\\\\u?0*(?:72|3a))(JH[s-v]|[\\x2b\\x2f-9A-Za-z][CSiy]R7|[\\x2b\\x2f-9A-Za-z]{2}[048AEIMQUYcgkosw]ke[\\x2b\\x2f-9w-z]))'\n```\n\n## Hunting in your logs using Splunk\n\nYou can use this RegEx to search your indexed logs using the `| regex`\n[SPL](https://docs.splunk.com/Documentation/Splunk/latest/SearchReference/Regex) command\n\n```spl\nindex=\u003c...\u003e sourcetype=\u003c...\u003e\n| regex \"\u003cLog4ShellRex\u003e\"\n```\n\n```spl\nindex=\u003c...\u003e sourcetype=\u003c...\u003e\n| regex \"(?im)(?:^|[\\\\n]).*?(?:[\\\\x24]|%(?:25%?)*24|\\\\\\\\u?0*(?:44|24))(?:[\\\\x7b]|%(?:25%?)*7b|\\\\\\\\u?0*(?:7b|173))[^\\\\n]*?((?:j|%(?:25%?)*(?:4a|6a)|\\\\\\\\u?0*(?:112|6a|4a|152))[^\\\\n]*?(?:n|%(?:25%?)*(?:4e|6e)|\\\\\\\\u?0*(?:4e|156|116|6e))[^\\\\n]*?(?:d|%(?:25%?)*(?:44|64)|\\\\\\\\u?0*(?:44|144|104|64))[^\\\\n]*?(?:[i\\\\x{130}\\\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\\\\\u?0*(?:111|69|49|151|130|460|131|461))[^\\\\n]*?(?:[\\\\x3a]|%(?:25%?)*3a|\\\\\\\\u?0*(?:72|3a))[^\\\\n]*?((?:l|%(?:25%?)*(?:4c|6c)|\\\\\\\\u?0*(?:154|114|6c|4c))[^\\\\n]*?(?:d|%(?:25%?)*(?:44|64)|\\\\\\\\u?0*(?:44|144|104|64))[^\\\\n]*?(?:a|%(?:25%?)*(?:41|61)|\\\\\\\\u?0*(?:101|61|41|141))[^\\\\n]*?(?:p|%(?:25%?)*(?:50|70)|\\\\\\\\u?0*(?:70|50|160|120))(?:[^\\\\n]*?(?:[s\\\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\\\\\u?0*(?:17f|123|577|73|53|163)))?|(?:r|%(?:25%?)*(?:52|72)|\\\\\\\\u?0*(?:122|72|52|162))[^\\\\n]*?(?:m|%(?:25%?)*(?:4d|6d)|\\\\\\\\u?0*(?:4d|155|115|6d))[^\\\\n]*?(?:[i\\\\x{130}\\\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\\\\\u?0*(?:111|69|49|151|130|460|131|461))|(?:d|%(?:25%?)*(?:44|64)|\\\\\\\\u?0*(?:44|144|104|64))[^\\\\n]*?(?:n|%(?:25%?)*(?:4e|6e)|\\\\\\\\u?0*(?:4e|156|116|6e))[^\\\\n]*?(?:[s\\\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\\\\\u?0*(?:17f|123|577|73|53|163))|(?:n|%(?:25%?)*(?:4e|6e)|\\\\\\\\u?0*(?:4e|156|116|6e))[^\\\\n]*?(?:[i\\\\x{130}\\\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\\\\\u?0*(?:111|69|49|151|130|460|131|461))[^\\\\n]*?(?:[s\\\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\\\\\u?0*(?:17f|123|577|73|53|163))|(?:[^\\\\n]*?(?:[i\\\\x{130}\\\\x{131}]|%(?:25%?)*(?:49|69|C4%(?:25%?)*B0|C4%(?:25%?)*B1)|\\\\\\\\u?0*(?:111|69|49|151|130|460|131|461))){2}[^\\\\n]*?(?:o|%(?:25%?)*(?:4f|6f)|\\\\\\\\u?0*(?:6f|4f|157|117))[^\\\\n]*?(?:p|%(?:25%?)*(?:50|70)|\\\\\\\\u?0*(?:70|50|160|120))|(?:c|%(?:25%?)*(?:43|63)|\\\\\\\\u?0*(?:143|103|63|43))[^\\\\n]*?(?:o|%(?:25%?)*(?:4f|6f)|\\\\\\\\u?0*(?:6f|4f|157|117))[^\\\\n]*?(?:r|%(?:25%?)*(?:52|72)|\\\\\\\\u?0*(?:122|72|52|162))[^\\\\n]*?(?:b|%(?:25%?)*(?:42|62)|\\\\\\\\u?0*(?:102|62|42|142))[^\\\\n]*?(?:a|%(?:25%?)*(?:41|61)|\\\\\\\\u?0*(?:101|61|41|141))|(?:n|%(?:25%?)*(?:4e|6e)|\\\\\\\\u?0*(?:4e|156|116|6e))[^\\\\n]*?(?:d|%(?:25%?)*(?:44|64)|\\\\\\\\u?0*(?:44|144|104|64))[^\\\\n]*?(?:[s\\\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\\\\\u?0*(?:17f|123|577|73|53|163))|(?:h|%(?:25%?)*(?:48|68)|\\\\\\\\u?0*(?:110|68|48|150))(?:[^\\\\n]*?(?:t|%(?:25%?)*(?:54|74)|\\\\\\\\u?0*(?:124|74|54|164))){2}[^\\\\n]*?(?:p|%(?:25%?)*(?:50|70)|\\\\\\\\u?0*(?:70|50|160|120))(?:[^\\\\n]*?(?:[s\\\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\\\\\u?0*(?:17f|123|577|73|53|163)))?)[^\\\\n]*?(?:[\\\\x3a]|%(?:25%?)*3a|\\\\\\\\u?0*(?:72|3a))|(?:b|%(?:25%?)*(?:42|62)|\\\\\\\\u?0*(?:102|62|42|142))[^\\\\n]*?(?:a|%(?:25%?)*(?:41|61)|\\\\\\\\u?0*(?:101|61|41|141))[^\\\\n]*?(?:[s\\\\x{17f}]|%(?:25%?)*(?:53|73|C5%(?:25%?)*BF)|\\\\\\\\u?0*(?:17f|123|577|73|53|163))[^\\\\n]*?(?:e|%(?:25%?)*(?:45|65)|\\\\\\\\u?0*(?:45|145|105|65))[^\\\\n]*?(?:[\\\\x3a]|%(?:25%?)*3a|\\\\\\\\u?0*(?:72|3a))(JH[s-v]|[\\\\x2b\\\\x2f-9A-Za-z][CSiy]R7|[\\\\x2b\\\\x2f-9A-Za-z]{2}[048AEIMQUYcgkosw]ke[\\\\x2b\\\\x2f-9w-z]))\"\n```\n\n## Screenshot\n\n**regex101**\n![Example Screenshot regex101](screenshots/example_4a.png)\n\n**grep -P**\n![Example Screenshot Shell](screenshots/example_4b.png)\n\n**Splunk**\n![Example Screenshot Splunk](screenshots/example_4c.jpeg)\n\n**Graphical representation of the RegEx**\n![Example Screenshot Splunk](screenshots/viz_4.png)\n(Created using regexper tool from Jeff Avallone, licensed under \n[CC BY license](https://creativecommons.org/licenses/by/3.0/).)\n\n## Other\n\n**Please create a pull request / issue if you can provide syntax for more systems.**\n\n## Credits\n\nI got help and ideas from:\n\n- [@cyberops](https://twitter.com/cyb3rops) building [log4shell-detector](https://github.com/Neo23x0/log4shell-detector/) that served as an inspiration\n- [@karanlyons](https://github.com/karanlyons) providing corpus to test against\n","project_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fback2root%2Flog4shell-rex","html_url":"https://awesome.ecosyste.ms/projects/github.com%2Fback2root%2Flog4shell-rex","lists_url":"https://awesome.ecosyste.ms/api/v1/projects/github.com%2Fback2root%2Flog4shell-rex/lists"}