The function from_base64() in src/libopensc/base64.c assumes signed chars.  With unsigned chars, bin_table can be indexed out of bounds:

static int from_base64(const char *in, unsigned int *out, int *skip)
{
	unsigned int res = 0, c, s = 18;
	const char *in0 = in;
	
	for (c = 0; c < 4; c++, in++) {
		u8 b;
		int k = *in;
		
		if (k < 0)
			return -1;
		if (k == 0 && c == 0)
			return 0;
		b = bin_table[k];


The exact impact of this bug depends on the image layout chosen by the linker.  bin_table should end up in the text section, so no information leak is expected, and the worst that could happen is likely a crash.