1/3/2024 0 Comments Certutil decode base64![]() ![]() E-Tag is used to identify a specific version of a file, If the file changes then the E-Tag changes.Īs you can see the metadata file contains a lot of useful information, However there is a lot more data that is unknown (highlighted with red color). This is the E-Tag header of the file from the HTTP response. The following are some of the hashing algorithms observed during analysis: The URL from where the file was downloaded The file last modification time header from the reponse ( Thanks to on Twitter for pointing that out ) The last time the file was downloaded in FILETIME format. x70x00x00x00 might be the header length (112 bytes). The URL and the MD5 hash can be extracted easily, But what about the header (116 bytes) ? the following summarize my findings: However C:\Users\u0041\AppData\LocalLow\Microsoft\CryptnetUrlCache\MetaData\BC456035A9E2885290EDC953764CC761 contains UTF-16LE encode URL and MD5 hash for the downloaded file in addition to some binary data: The file located on C:\Users\u0041\AppData\LocalLow\Microsoft\CryptnetUrlCache\Content\BC456035A9E2885290EDC953764CC761 contains the actual file: The file name BC456035A9E2885290EDC953764CC761 is the MD5 hash for the URL UTF-16LE encode: The following command will download mimkatz from github and save it to the current directory ( C:\windows\temp):Īfter executing the above command we can see in procmon that is writing to two files:īoth files have the same name but on different directories. In this example we will download a file using certutil and observe the files written to the system. ![]() In this blog we will take a look at the artifacts generated by certutil when downloading a file, specifically the metadata file, analyze it's structure and write a parser for it. However certutil could be used to base64 encode/decode, calculate file hashes and download files from the internet. ![]() Certutil is a build-in tool on windows systems that is used to manage certificates. ![]()
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