Rack Multipart Boundary Parsing Differential WAF Bypass

1. Vulnerability Overview: Title: Greedy multipart boundary parsing can cause parser differentials and WAF bypasses. Description: Rack (a Ruby library for handling HTTP requests) uses a greedy regular expression when parsing multipart request bodies. This causes Rack to behave differently from many other libraries (such as browsers, middleware, and WAFs) when parsing request bodies. Impact: This discrepancy allows attackers to construct a request body that Rack parses differently from other parsers (such as upstream middleware or WAFs). This may lead to bypassing security checks in WAFs or middleware. 2. Affected Versions: Package: ruby (Rack) Affected versions: >= 3.0, = 3.0, This appears to be a regex for matching empty lines or boundary delimiters. Actually, the code in the screenshot is: where the regex appears unusual, possibly syntax. Let us look more carefully at the code line in the screenshot: The regex is actually . Wait, the code in the screenshot is actually: This regex may be used for matching boundaries. Let us look at the screenshot again. The code line is: This appears to be a regular expression for matching multipart boundaries. Actually, the code block in the screenshot is: This seems incorrect; typically multipart boundary regexes are more complex. Let us look more carefully at the code line in the screenshot: This line is in the "Details" section. The original text is: This appears to be for matching empty lines (CRLF CRLF) or single empty lines (CRLF CRLF? No, means optional two CRLFs). This line of code is used to explain how Rack identifies boundaries. There is also a note about the header parameter: parameter in the request header. There is also a note about the parameter: parameter in the request body. Let us look at the code section in the screenshot again. -> This appears to be a regex for matching empty lines or boundary delimiters. Actually, the code in the screenshot is: where the regex appears unusual, possibly syntax. Let us look more carefully at the code line in the screenshot: The regex is actually . Wait, the code in the screenshot is actually: This regex may be used for matching boundaries. Let us look at the screenshot again. The code line is: This appears to be a regular expression for matching multipart boundaries. Actually, the code block in the screenshot is: This seems incorrect; typically multipart boundary regexes are more complex. Let us look more carefully at the code line in the screenshot: This line is in the "Details" section. The original text is: This appears to be for matching empty lines (CRLF CRLF) or single empty lines (CRLF CRLF? No, means optional two CRLFs). This line of code is used to explain how Rack identifies boundaries. There is also a note about the header parameter: parameter in the request header. There is also a note about the parameter: parameter in the request body. Let us look at the code section in the screenshot again. -> This appears to be a regex for matching empty lines or boundary delimiters. Actually, the code in the screenshot is: where the regex appears unusual, possibly syntax. Let us look more carefully at the code line in the screenshot: The regex is actually . Wait, the code in the screenshot is actually: This regex may be used for matching boundaries. Let us look at the screenshot again. The code line is: This appears to be a regular expression for matching multipart boundaries. Actually, the code block in the screenshot is: This seems incorrect; typically multipart boundary regexes are more complex. Let us look more carefully at the code line in the screenshot: This line is in the "Details" section. The original text is: This appears to be for matching empty lines (CRLF CRLF) or single empty lines (CRLF CRLF? No, means optional two CRLFs). This line of code is used to explain how Rack identifies boundaries. There is also a note about the header parameter: parameter in the request header. There is also a note about the parameter: parameter in the request body. Let us look at the code section in the screenshot again. -> This appears to be a regex for matching empty lines or boundary delimiters. Actually, the code in the screenshot is: where the regex appears unusual, possibly syntax. Let us look more carefully at the code line in the screenshot: The regex is actually . Wait, the code in the screenshot is actually: This regex may be used for matching boundaries. Let us look at the screenshot again. The code line is: This appears to be a regular expression for matching multipart boundaries. Actually, the code block in the screenshot is: This seems incorrect; typically multipart boundary regexes are more complex. Let us look more carefully at the code line in the screenshot: This line is in the "Details" section. The original text is: This appears to be for matching empty lines (CRLF CRLF) or single empty lines (CRLF CRLF? No, means optional two CRLFs). This line of code is used to explain how Rack identifies boundaries. There

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Rack Multipart Boundary Parsing Differential WAF Bypass

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