The CERT C Programming Language Secure Coding Standard was developed specifically for versions of the C programming language defined by
ISO/IEC 9899:1999 Programming Languages — C, Second Edition [[ISO/IEC 9899:1999]]
- Technical corrigenda TC1, TC2, and TC3
ISO/IEC TR 24731-1 Extensions to the C Library, Part I: Bounds-checking interfaces [[ISO/IEC TR 24731-1-2007]]
- ISO/IEC WDTR 24731-2 Extensions to the C Library, Part II: Dynamic Allocation Functions
Most of the material included in this standard can also be applied to earlier versions of the C programming language.
Rules and recommendations included in this standard are designed to be operating system and platform independent. However, the best available solutions to these problems are often platform specific. In most cases, we have attempted to provide appropriate compliant solutions for POSIX-compliant and Windows operating systems. In many cases, compliant solutions have also been provided for specific platforms such as Linux or OpenBSD. Occasionally, we also point out implementation-specific behaviors when these behaviors are of interest.
Rationale
A secure coding standard for the C programming language can create the highest value for the longest period of time by focusing on C99 and the relevant post-C99 technical reports. In addition, more code remains to be written than has already been written, so the highest return on investment comes from influencing programmers who are developing new code; although maintaining old code is still important.
The C standard documents existing practice where possible. That is, most features must be tested in an implementation before being included in the standard. The CERT C secure coding standard has a different purpose. When existing practice serves this purpose, that is fine, but the goal is to create a new set of best practices, and that includes introducing some concepts that are not yet widely known. To put it a different way, the C secure coding guidelines are attempting to drive change rather than just document it.
For example, the C library technical report, part 1 (TR 24731-1) is catching on, but at present is only implemented by a few vendors. It introduces functions such as memcpy_s(), which serve the purpose of security by adding the destination buffer size to the API. A forward looking document could not reasonably ignore these simply because they are not yet widely implemented.
C99 is more widely implemented, but even if it were not yet, it is the direction in which the industry is moving. Developers of new C code, especially, need guidance that is usable on and makes the best use of the compilers and tools that are now being developed and are being supported into the future.
Some vendors have extensions to C, and some also have implemented only part of the C standard before stopping development. Consequently, it is not possible to back up and only discuss C95, or C90. The vendor support equation is too complicated to draw a line and say that a certain compiler supports exactly a certain standard. Whatever demarcation point is selected, different vendors are be on opposite sides of it for different parts of the language. Supporting all possibilities would require testing the cross product of each compiler with each language feature. Consequently we have selected a demarcation point that is the most recent in time, so that the rules and recommendations defined by the standard will be applicable for as long as possible.
The value of forward looking information increases with time before it starts to decrease. The value of backward looking information starts to decrease immediately.
For all these reasons, the priority of this standard is to support new code development using C99 and the post-C99 technical reports. A close second priority is supporting remediation of old code using C99 and the TRs.
This standard does try to make contributions to support older compilers when these contributions can be significant and doing so does not compromise other priorities. The intent is not to capture all deviations from the standard; only a few important ones.