1. Banned APIs and Sin Within!
Michael Howard

2. Who Is This Guy? mikehow@microsoft.com
Christian (imperfect in every possible way!)
Microsoft employee for 20 years
Always in security
Worked on the Microsoft SDL since inception

3. Goals and Non-Goals I am not one for drawing analogies
“Security Analogies are usually Wrong”
I use quotes from the Bible to compare/contrast software security
“The Bible is correct, your code is not.” :-)

4. If cars operated in an environment like the Internet, they would…
Be driven by people with little regard for safe automobile operation.
Have their windshields shot out every 60 secs.
Once you have bullet-proof glass, the bad guys place nails at freeway off-ramps next to signs like, “free coffee this way”
and someone is always trying to steal your keys
and pull out your sparkplugs
and siphon your gas
Talking of gas, you fill up at a Shell station, only to realize the gas really isn’t gas, it’s vegetable oil and sand
Oh, that gas station isn’t a Shell station, it certainly looked like one, but they took your credit card details anyway
As this all goes on, you can’t see the adversary
And the adversaries are sharing new weapons with each other

5. The SDL A set of process changes that help improve software security
Over 100 requirements and recommendations
About 30 deal with memory corruption
Removing banned APIs is one such requirement

6. What Are The Banned APIs?
Mostly memory corruption APIs
strcpy …
strcat …
strncpy …
strncat …
sprintf …
gets …

7. Banned APIs
strcpy, strcpyA, strcpyW, wcscpy, _tcscpy, _mbscpy, StrCpy, StrCpyA, StrCpyW, lstrcpy, lstrcpyA, lstrcpyW, _tccpy, _mbccpy
strcat, strcatA, strcatW, wcscat, _tcscat, _mbscat, StrCat, StrCatA, StrCatW, lstrcat, lstrcatA, lstrcatW, StrCatBuff, StrCatBuffA, StrCatBuffW, StrCatChainW, _tccat, _mbccat
strncpy, wcsncpy, _tcsncpy, _mbsncpy, _mbsnbcpy, StrCpyN, StrCpyNA, StrCpyNW, StrNCpy, strcpynA, StrNCpyA, StrNCpyW, lstrcpyn, lstrcpynA, lstrcpynW
strncat, wcsncat, _tcsncat, _mbsncat, _mbsnbcat, StrCatN, StrCatNA, StrCatNW, StrNCat, StrNCatA, StrNCatW, lstrncat, lstrcatnA, lstrcatnW, lstrcatn
CharToOem, CharToOemA, CharToOemW, OemToChar, OemToCharA, OemToCharW, CharToOemBuffA, CharToOemBuffW
wnsprintf, wnsprintfA, wnsprintfW, sprintfW, sprintfA, wsprintf, wsprintfW, wsprintfA, sprintf, swprintf, _stprintf, _snwprintf, _snprintf, _sntprintf, wvsprintf, wvsprintfA, wvsprintfW, vsprintf, _vstprintf, vswprintf, _vsnprintf, _vsnwprintf, _vsntprintf, wvnsprintf, wvnsprintfA, wvnsprintfW
strtok, _tcstok, wcstok, _mbstok
makepath, _tmakepath, _makepath, _wmakepath, _splitpath, _tsplitpath, _wsplitpath
scanf, wscanf, _tscanf, sscanf, swscanf, _stscanf, snscanf, snwscanf, _sntscanf
_itoa, _itow, _i64toa, _i64tow, _ui64toa, _ui64tot, _ui64tow, _ultoa, _ultot, _ultow
gets, _getts, _gettws
IsBadWritePtr, IsBadHugeWritePtr, IsBadReadPtr, IsBadHugeReadPtr, IsBadCodePtr, IsBadStringPtr
memcpy

8. PnP MS05-039 Zotob CONFIGRET ResDesToNtResource(
IN PCVOID ResourceData,
IN RESOURCEID ResourceType,
IN ULONG ResourceLen,
IN PCM_PARTIAL_RESOURCE_DESCRIPTOR pResDes,
IN ULONG ulTag ) {
case ResType_ClassSpecific: {
PCS_RESOURCE pCsData = (PCS_RESOURCE)ResourceData;
LPBYTE ptr = NULL;
ptr = (LPBYTE)((LPBYTE)pResDes sizeof(CM_PARTIAL_RESOURCE_DESCRIPTOR));
memcpy(ptr,
pCsData->CS_Header.CSD_Signature pCsData->CS_Header.CSD_LegacyDataOffset,
pCsData->CS_Header.CSD_LegacyDataSize);

9. PCT SChannel MS04-011 #define SSL2_MAX_CHALLENGE_LEN 32
typedef struct _Ssl2_Client_Hello { DWORD dwVer; DWORD cCipherSpecs; DWORD cbSessionID; DWORD cbChallenge; UCHAR SessionID[SSL3_SESSION_ID_LEN]; UCHAR Challenge[SSL2_MAX_CHALLENGE_LEN]; Ssl2_Cipher_Kind CipherSpecs[MAX_UNI_CIPHERS];
} Ssl2_Client_Hello, * PSsl2_Client_Hello;
SP_STATUS Pct1SrvHandleUniHello(..., PSsl2_Client_Hello pHello,...) { Pct1_Client_Hello ClientHello;
...
CopyMemory( ClientHello.Challenge, pHello->Challenge, pHello->cbChallenge);

10. NNTP MS05-030
HRESULT CNewsStore::OnResponse(LPNNTPRESPONSE pResponse) {
...
if (pResponse->state == NS_LIST)
hr = _HandleListResponse(pResponse, FALSE) }
HRESULT CNewsStore::_HandleListResponse(LPNNTPRESPONSE pResp, BOOL fNew) {
LPSTR psz, pszCount;
int nSize;
char szGroupName[CCHMAX_FOLDER_NAME];
LPNNTPLIST pnl = &pResp->rList;
for (DWORD i = 0; i < pnl->cLines; i++, m_op.dwProgress++) {
psz = pnl->rgszLines[i];
while (*psz && !IsSpace(psz))
psz = CharNext(psz);
nSize = (int)(psz - pnl->rgszLines[i]);
if (nSize >= CCHMAX_FOLDER_NAME)
nSize = CCHMAX_FOLDER_NAME - 1;
CopyMemory(szGroupName, pnl->rgszLines[i], nSize);
Last Updated

11. LSASS MS04-011 Sasser VOID DsRolepDebugDumpRoutine(
IN DWORD DebugFlag,
IN LPWSTR Format,
va_list arglist
) {
#define DsRolepDebugDumpRoutine_BUFFERSIZE 1024
WCHAR OutputBuffer[DsRolepDebugDumpRoutine_BUFFERSIZE];
...
length += (ULONG) wvsprintfW(&OutputBuffer[length],
Format,
arglist); }

12. How Do you Find Them?
#include <banned.h>
C4996 warnings

13. The Replacements Don’t use C++ as a glorified C! Use std::string
Use strsafe.h
Use strcpy_s etc

14. Auto-replacement of Banned Functions
If the compiler knows the destination buffer size at compile time, it can automatically generate secure code
Add the following to auto-migrate functions to safe functions
#define _CRT_SECURE_CPP_OVERLOAD_STANDARD_NAMES (1)
char buf[32];
strcpy(buf,src);
char buf[32];
strcpy_s(buf,src,32);

15. But Isn’t C dead?

16. The Leap of Faith What about regressions?
In ten years, I have seen only one regression at Microsoft

17. Effectiveness?
Over 25% of MSRC memory corruption vulns did not affect newer products simply because we banned the API(s) in question and replaced them with a more secure version
That’s low cost engineering at its best!

18. Pop Quiz What’s in an 8oz glass of wine?
What’s in an 8oz glass of poison?
What’s in an 8oz glass of wine with a drop of poison?

19. Sin and Insecure Code Righteous Man + One Sin Sinful Man
Well-Written Code
+ One Vulnerability
Insecure System

20. All Sin is the Same …
There is no “good” or “bad” sin, it’s all sin in God’s eyes.
There is no “Security Bulletin” scale for sin
Critical: Adultery, Murder
Important: Bearing False Witness
Moderate: Stealing
Low: Coveting

21. … but insecure Code is not the Same
An anonymously accessible remote code execution vulnerability that gives you root is *way* worse than a local information disclosure vuln accessibly only by admins
Critical: Remote code execution
Important: Server DoS
Moderate: Temporary Server DoS
Low: Client DoS

22. Banned APIs We have banned over 120 APIs at Microsoft
They are great examples of “One-line” Sins

23. Removing Sin How do you remove Sin?
By replacing Sin with something not Sinful!
Easy to say, very hard to do.
How do you remove banned APIs?
By replacing them with something less dangerous!
Easy to say, easy to do.
And I know that nothing good lives in me, that is, in my sinful nature. I want to do what is right, but I can't.
Romans 7:18

24. Removal takes a Leap of Faith
Trust that God forgives your Sins
Trust that the banned API replacements don’t introduce regressions!
Praise the Lord, … who forgives all your sins.
Psalm 103:3

25. How Do you Remove Banned APIs?
Admit you have banned APIs (admit you sin!)
Do something about it (admit the Lord into your heart)
Don’t repeat!

26. Banned APIs and the Sin Within Summary
Admit you sin
In life and in code
Do something about it
Study Romans
Remove Banned APIs
Put steps in place to help prevent Sin and banned APIs
Think!!
Use banned.h in all your C/C++ code

27. Questions!?