Fix potential DoS by limiting number sizes in exponentiation
Check that the exponent and modulus is below `MBEDTLS_MPI_MAX_BITS` before
performing a time expensive operation (modular exponentiation). This prevents
a potential DoS from Diffie-Hellman computations with extremely
large key sizes.
@@ -2115,6 +2115,10 @@ int mbedtls_mpi_exp_mod( mbedtls_mpi *X, const mbedtls_mpi *A,
if( mbedtls_mpi_cmp_int( E, 0 ) < 0 )
return( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
+ if( mbedtls_mpi_bitlen( E ) > MBEDTLS_MPI_MAX_BITS ||
+ mbedtls_mpi_bitlen( N ) > MBEDTLS_MPI_MAX_BITS )
+ return ( MBEDTLS_ERR_MPI_BAD_INPUT_DATA );
+
/*
* Init temps and window size
*/
