|Each vulnerability which allows us to modify memory areas
beyond some input variable, opens the threat that some
jump address (usually return addresses) can be manipulated
to execute malicious code which has been loaded in some buffer.
|Exploits will be developed for known vulnerabilities
even if it can be at times pretty challenging.
|The standard C library provides many functions which
modify a string without knowing its length (examples: strcat,
sprintf). It took some time until alternative variants
with length parameters became available.
|Security fixes attempted in many cases to limit the
input and to use some estimates of the maximal length if
the input was used elsewhere. Many software authors trusted
their calculations and continued with the traditional
programming style. Unfortunately, many of these estimates
were simply wrong and allowed future exploits.
|Consequently, buffer limits should be verified everywhere.
|If the C programming language cannot be avoided,
it is best to forget the C standard library and buffers
of limited length. Instead, libraries that support dynamic
strings should be taken. The only author of network services
who does this thoroughly is Dan J. Bernstein (Qmail, djbdns). |
|Copyright © 2001, 2002 Andreas Borchert, converted to HTML on April 07, 2002|