Magic bytes
A signature byte sequence at a fixed offset at the beginning of a file, defined by format specifications, used to determine a file's true type without decoding the entire file.
Timeline (last 90 days)
Magic bytes are characteristic byte sequences at fixed offsets at the start of a file, defined by format specifications, used to determine the true type without decoding the entire file; Windows executables start with MZ (0x4D 0x5A), PDFs start with %PDF, PNGs start with \x89PNG, and ZIP and its derivative formats start with PK\x03\x04.
Magic bytes sniffing usually reads only the first few dozen to few hundred bytes of a file and can only identify formats with clear header signatures; it struggles to determine plain text, CSV, Markdown, and the like that have no fixed signature, requiring additional heuristic rules.
Magic bytes sniffing must be used together with an explicit allowlist: reject on a failed match rather than guessing.
All Facts (3)
Magic bytes are characteristic byte sequences at fixed offsets at the start of a file, defined by format specifications, used to determine the true type without decoding the entire file; Windows executables start with MZ (0x4D 0x5A), PDFs start with %PDF, PNGs start with \x89PNG, and ZIP and its derivative formats start with PK\x03\x04.
50%UnverifiedMagic bytes sniffing usually reads only the first few dozen to few hundred bytes of a file and can only identify formats with clear header signatures; it struggles to determine plain text, CSV, Markdown, and the like that have no fixed signature, requiring additional heuristic rules.
50%UnverifiedMagic bytes sniffing must be used together with an explicit allowlist: reject on a failed match rather than guessing.
50%