OpenGL - Texture not rendering properly

I'm trying to render a cube with a wood texture (all faces of the cube with the same texture), but the texture is not being rendered as it should (looks like the texture is trasparent at some parts):

But if look inside the cube, it seems to be rendering properly:

:

Here is the .obj file that I'm reading from (with the texture coords and vertices):

mtllib crate.mtl
o Cube_Cube.002
v -1.000000 -1.000000 1.000000
v -1.000000 -1.000000 -1.000000
v 1.000000 -1.000000 -1.000000
v 1.000000 -1.000000 1.000000
v -1.000000 1.000000 1.000000
v -1.000000 1.000000 -1.000000
v 1.000000 1.000000 -1.000000
v 1.000000 1.000000 1.000000
vt 1.000000 0.000000
vt 0.000000 1.000000
vt 0.000000 0.000000
vt 1.000000 0.000000
vt 0.000000 1.000000
vt 0.000000 0.000000
vt 1.000000 0.000000
vt 0.000000 1.000000
vt 0.000000 0.000000
vt 1.000000 0.000000
vt 0.000000 1.000000
vt 0.000000 0.000000
vt 1.000000 0.000000
vt 0.000000 0.000000
vt 0.000000 1.000000
vt 1.000000 1.000000
vt 1.000000 1.000000
vt 1.000000 1.000000
vt 1.000000 1.000000
vt 1.000000 1.000000
vn -1.0000 0.0000 0.0000
vn 0.0000 0.0000 -1.0000
vn 1.0000 0.0000 0.0000
vn 0.0000 0.0000 1.0000
vn 0.0000 -1.0000 0.0000
vn 0.0000 1.0000 0.0000
usemtl Material
s off
f 6/1/1 1/2/1 5/3/1
f 7/4/2 2/5/2 6/6/2
f 8/7/3 3/8/3 7/9/3
f 5/10/4 4/11/4 8/12/4
f 2/13/5 4/11/5 1/14/5
f 7/4/6 5/15/6 8/12/6
f 6/1/1 2/16/1 1/2/1
f 7/4/2 3/17/2 2/5/2
f 8/7/3 4/18/3 3/8/3
f 5/10/4 1/19/4 4/11/4
f 2/13/5 3/17/5 4/11/5
f 7/4/6 6/20/6 5/15/6

Here is the way I'm loading the texture to OpenGL:

unsigned char* localBuffer = stbi_load(filepath.c_str(), &this->width, &this->height, &this->bitsPerPixel, 4);

glGenTextures(1, &this->id);
glActiveTexture(GL_TEXTURE0 + this->slot);
glBindTexture(GL_TEXTURE_2D, this->id);

glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);

glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA8, this->width, this->height, 0, GL_RGBA, GL_UNSIGNED_BYTE, localBuffer);
glBindTexture(GL_TEXTURE_2D, 0);

Here is the the vertex shader:

layout (location = 0) in vec3 aPos;
layout (location = 1) in vec2 textureCoords;

out vec2 vTextureCoords;

uniform mat4 Mvp;

void main()
{
   vTextureCoords = textureCoords;
   gl_Position = Mvp * vec4(aPos, 1.0);
}

Here is the fragment shader:

out vec4 FragColor;

in vec2 vTextureCoords;

uniform sampler2D textureSlot;

void main()
{
    FragColor = texture(textureSlot, vTextureCoords);
} 

Can someone tell me what I'm doing wrong here?

Thanks to @Sync it I find out that the solution was to enable depth testing.

glEnable(GL_DEPTH_TEST);