Uncontrolled format string

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Uncontrolled format string is a type of <a href="/facts/Code_injection/6gPRDpd1">code injection</a> <a href="/facts/Software_vulnerability/jg0Gr71M">vulnerability</a> discovered around 1989 that can be used in <a href="/facts/Security_exploit/EdlqsRJM">security exploits</a>. Originally thought harmless, format string exploits can be used to <a href="/facts/Crash_(computing)/I8yn65yt">crash</a> a program or to execute harmful code. The problem stems from the use of <a href="/facts/Unchecked_user_input/4967Sm1s">unchecked user input</a> as the format string parameter in certain <a href="/facts/C_(programming_language)/Ky2No763">C</a> functions that perform formatting, such as <a href="/facts/Printf/Sc6Czbp2">printf()</a>. A malicious user may use the %s and %x format tokens, among others, to print data from the <a href="/facts/Call_stack/1sMt713v">call stack</a> or possibly other locations in memory. One may also write arbitrary data to arbitrary locations using the %n format token, which commands printf() and similar functions to write the number of bytes formatted to an address stored on the stack.
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Uncontrolled format string open-in-new

Uncontrolled format string