centos 7
format weakness #27

4

Weakness Breakdown


Definition:

A format string exploit occurs when the data of an input string is evaluated as a command by the program. This class of attacks is very similar to buffer overflows since an attacker could execute code, read the stack or cause new behaviors that compromise security. Learn more about format string attacks on OWASP attack index.

Warning code(s):

If format strings can be influenced by an attacker, they can be exploited.

File Name:

cpuid-20170122/cpuid.c

Context:

The highlighted line of code below is the trigger point of this particular Centos 7 format weakness.

 #define __TF(v)    ((v) & 0x0ff03f00)
#define __TFM(v)   ((v) & 0x0fff3ff0)
#define __TFMS(v)  ((v) & 0x0fff3fff)

#define _T(v)      ((v) << 12)
#define _F(v)      ((v) << 8)
#define _M(v)      ((v) << 4)
#define _S(v)      (v)
#define _XF(v)     ((v) << 20)
#define _XM(v)     ((v) << 16)

#define __B(v)     ((v) & 0x000000ff)
#define _B(v)      (v)

#define _FM(xf,f,xm,m)     (_XF(xf) + _F(f) + _XM(xm) + _M(m))
#define _FMS(xf,f,xm,m,s)  (_XF(xf) + _F(f) + _XM(xm) + _M(m) + _S(s))

#define START \
   if (0)
#define F(xf,f,str) \
   else if (__F(val)    ==       _XF(xf)        +_F(f)                              ) printf(str)
#define FM(xf,f,xm,m,str) \
   else if (__FM(val)   ==       _XF(xf)+_XM(xm)+_F(f)+_M(m)                        ) printf(str)
#define FMS(xf,f,xm,m,s,str) \
   else if (__FMS(val)  ==       _XF(xf)+_XM(xm)+_F(f)+_M(m)+_S(s)                  ) printf(str)
#define TF(t,xf,f,str) \
   else if (__TF(val)   == _T(t)+_XF(xf)        +_F(f)                              ) printf(str)
#define TFM(t,xf,f,xm,m,str) \
   else if (__TFM(val)  == _T(t)+_XF(xf)+_XM(xm)+_F(f)+_M(m)                        ) printf(str)
#define TFMS(t,xf,f,xm,m,s,str) \
   else if (__TFMS(val) == _T(t)+_XF(xf)+_XM(xm)+_F(f)+_M(m)+_S(s)                  ) printf(str)
#define FQ(xf,f,q,str) \
   else if (__F(val)    ==       _XF(xf)        +_F(f)             && (stash) && (q)) printf(str)
#define FMQ(xf,f,xm,m,q,str) \
   else if (__FM(val)   ==       _XF(xf)+_XM(xm)+_F(f)+_M(m)       && (stash) && (q)) printf(str)
#define FMSQ(xf,f,xm,m,s,q,str) \
   else if (__FMS(val)  ==       _XF(xf)+_XM(xm)+_F(f)+_M(m)+_S(s) && (stash) && (q)) printf(str)
#define DEFAULT(str) \
   else                                                                               printf(str)
#define FALLBACK(code) \
   else code

typedef struct {
   vendor_t       vendor;
   boolean        saw_4;
   boolean        saw_b;
   unsigned int   val_0_eax;
   unsigned int   val_1_eax;
   unsigned int   val_1_ebx;
   unsigned int   val_1_ecx; 

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