owasp-amass/amass · error

IP address parsing failed

Error message

IP address parsing failed

What it means

ParseIPs is a flag.Value implementation for comma-separated IP address/range flags. Set rejects an empty string with this error before doing any parsing. Non-empty input must consist of comma-separated entries each of which is a resolvable range, a parseable IP, or a CIDR.

Source

Thrown at internal/afmt/parse.go:100

func (p *ParseIPs) String() string {
	if p == nil {
		return ""
	}
	var builder strings.Builder
	for i, ipaddr := range *p {
		if i > 0 {
			builder.WriteRune(',')
		}
		builder.WriteString(ipaddr.String())
	}
	return builder.String()
}

// Set implements the flag.Value interface.
func (p *ParseIPs) Set(s string) error {
	if s == "" {
		return fmt.Errorf("IP address parsing failed")
	}

	for _, v := range strings.Split(s, ",") {
		if start, end, ok := parseRange(v); ok {
			ips := amassnet.RangeHosts(start, end)
			if len(ips) == 0 {
				return fmt.Errorf("%s is not a valid IP address or range", v)
			}
			for _, ip := range ips {
				*p = append(*p, ip)
			}
			continue
		} else if ip := net.ParseIP(v); ip != nil {
			*p = append(*p, ip)
			continue
		} else {
			return fmt.Errorf("%s is not a valid IP address or range", v)
		}

View on GitHub (pinned to 79299dce87)

Solutions

1. Provide a non-empty comma-separated value such as "192.168.1.1,10.0.0.0/24".
2. Guard the variable in the shell (test -n) before invoking the command.
3. Omit the flag entirely when no IPs are needed.

Example fix

// before
-ip "$IPS"    # IPS empty -> IP address parsing failed
// after
-ip "192.168.1.1,192.168.1.10-20,10.0.0.0/24"

func validateIPsFlag(value string) error {
	if strings.TrimSpace(value) == "" {
		return errors.New("flag requires at least one IP, range, or CIDR")
	}
	for _, v := range strings.Split(value, ",") {
		if net.ParseIP(strings.TrimSpace(v)) == nil && !strings.Contains(v, "-") && !strings.Contains(v, "/") {
			return fmt.Errorf("entry %q is not an IP, range, or CIDR", v)
		}
	}
	return nil
}

func isIPOrRange(s string) bool { return net.ParseIP(s) != nil || strings.ContainsAny(s, "-/") }

When it happens

Trigger: Calling Set("") on a *ParseIPs, e.g. `-ip "$IP_LIST"` where IP_LIST is empty, or passing `-ip ""` in a script with an unset variable.

Common situations: Empty environment variables in scripts, CI templates with missing inputs, or mistaken attempts to clear a default flag value with an empty string.

Understand the failure class

Background: "unknown output mode", "invalid value for flag", "expects true/false": fixing invalid flag value errors in CLI tools — this error's family across 24 libraries.

Related errors

• %s is not a valid IP address or range
• %s is not a valid CIDR
• failed to parse %s as a CIDR
• IP address parsing failed
• String parsing failed

AI-assisted analysis of owasp-amass/amass@79299dce87 (2026-09-06). Data as JSON: /api/errors/8c48d05845fbd828. Report an issue: GitHub.