Language: C
Label: vulnerable
CWE: CWE-74 \u2014 Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')
The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.

Code:
int valid_field (const char *field, const char *illegal)
{
	const char *cp;
	int err = 0;

	if (NULL == field) {
		return -1;
	}

	/* For each character of field, search if it appears in the list
	 * of illegal characters. */
	for (cp = field; '\0' != *cp; cp++) {
		if (strchr (illegal, *cp) != NULL) {
			err = -1;
			break;
		}
	}

	if (0 == err) {
		/* Search if there are some non-printable characters */
		for (cp = field; '\0' != *cp; cp++) {
			if (!isprint (*cp)) {
				err = 1;
				break;
			}
		}
	}

	return err;
}