A vulnerable JPEG renderer could then be coerced into executing the payload, handing control to the attacker. Security Implications Ī polyglot of two formats may steganographically compose a malicious payload within an ostensibly benign and widely accepted wrapperįormat, such as a JPEG file that allows arbitrary data in its comment field. The Python 2 and Python 3 programming languages were not designed to be compatible with each other, but there is sufficient commonality of syntax that a polyglot Python program can be written than runs in both versions. The DICOM medical imaging format was designed to allow polyglotting with TIFF files, allowing efficient storage of the same image data in a file that can be interpreted by either DICOM or TIFF viewers. For example, to add an empty textarea to a page, one cannot use, but has to use instead. In a polyglot markup document non-void elements (such as script, p, div) cannot be self-closing even if they are empty, as this is not valid HTML. The most basic possible polyglot markup document would therefore look like this: pre and textarea should not start with newline character) Use self-closing tags for void elements.) Specifying a document’s character encoding.Processing instructions and the XML declaration are both forbidden in polyglot markup.The same document can then be served as either HTML or XHTML, depending on browser support and MIME type.Īs expressed by the html-polyglot recommendation, to write a polyglot HTML5 document, the following key points should be observed: For example, in order for an HTML5 document to meet these criteria, the two requirements are that it must have an HTML5 doctype, and be written in well-formed XHTML. Such documents can be parsed as either HTML (which is SGML-compatible) or XML, and will produce the same DOM structure either way. Polyglot markup has been proposed as a useful combination of the benefits of HTML5 and XHTML. The following is written simultaneously in SNOBOL4, Win32Forth, PureBasicv4.x, and REBOL: SNOBOL4, Win32Forth, PureBasicv4.x, and REBOL In PHP the main function is defined but not called and in C there is no need to explicitly call the main function. The final three lines are only used by bash, to call the main function.printf is a bash shell builtin which is identical to the C printf except for its omission of brackets (which the C preprocessor adds if this is compiled with a C compiler)." if (($x))" is a valid statement in both bash and PHP.Comment indicators can be combined to perform various operations.The statement " function main()" is valid in both PHP and bash C #defines are used to convert it into " int main(void)" at compile time.Even on commented out lines, the " " PHP indicators still have effect.Shell redirection is used to eliminate undesirable outputs."//" is a comment in both PHP and C and the root directory in bash.A hash sign marks a preprocessor statement in C, but is a comment in both bash and PHP.Printf "Hello, world!\n"true/* 2> /dev/null | grep -v true*/ These are demonstrated in this public domain polyglot written in ANSI C, PHP and bash: ![]() Two commonly used techniques for constructing a polyglot program are to make use of languages that use different characters for comments, and to redefine various tokens as others in different languages. This is often accomplished by hiding language-specific constructs in segments interpreted as comments or plain text of the other format. To maintain validity across interpreting programs, one must ensure that constructs specific to one interpreter are not interpreted by another, and vice versa. For example, a PDF-Zip polyglot might be opened as both a valid PDF document and decompressed as a valid zip archive. A file is a valid polyglot if it can be successfully interpreted by multiple interpreting programs. ![]() Construction Ī polyglot is composed by combining syntax from two or more different formats, leveraging various syntactic constructs that are either common between the formats, or constructs that are language specific but carrying different meaning in each language. In the 21st century, polyglot programs and files gained attention as a covert channel mechanism for propagation of malware. In 2000, a polyglot program was named a winner in the International Obfuscated C Code Contest. A notable early example, named simply polyglot was published on the Usenet group rec.puzzles in 1991, supporting 8 languages, though this was inspired by even earlier programs. Polyglot programs have been crafted as challenges and curios in hacker culture since at least the early 1990s.
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