shadow1ng/fscan · error

parser_cidr_failed: %w

Error message

parser_cidr_failed: %w

What it means

Inside parseHostString, any comma-separated token containing '/' is treated as a CIDR and parsed by parseIPCIDR. On failure the error is wrapped with 'parser_cidr_failed' plus the offending token. It signals an invalid CIDR expression in the host list.

Source

Thrown at common/parsers/parsers.go:122

				return nil, err
			}
			hosts = append(hosts, cidrHosts...)
		case h == "172":
			cidrHosts, err := parseIPCIDR("172.16.0.0/12")
			if err != nil {
				return nil, err
			}
			hosts = append(hosts, cidrHosts...)
		case h == "10":
			cidrHosts, err := parseIPCIDR("10.0.0.0/8")
			if err != nil {
				return nil, err
			}
			hosts = append(hosts, cidrHosts...)
		case strings.Contains(h, "/"):
			cidrHosts, err := parseIPCIDR(h)
			if err != nil {
				return nil, fmt.Errorf(i18n.Tr("parser_cidr_failed", h)+": %w", err)
			}
			hosts = append(hosts, cidrHosts...)
		case strings.Contains(h, "-") && !strings.Contains(h, ":") && looksLikeIPRange(h):
			rangeHosts, err := parseIPRangeString(h)
			if err != nil {
				return nil, fmt.Errorf(i18n.Tr("parser_ip_range_failed", h)+": %w", err)
			}
			hosts = append(hosts, rangeHosts...)
		default:
			hosts = append(hosts, h)
		}
	}

	return hosts, nil
}

// =============================================================================
// 端口解析

View on GitHub (pinned to 95cc12e753)

Solutions

1. Fix the CIDR in the host argument (valid IPv4 + mask 0-32), e.g. 192.168.1.0/24
2. Remove non-CIDR tokens that merely contain '/'
3. Validate with net.ParseCIDR before calling ParseIP
4. If IPv6 is needed, confirm library support first — the matcher is IPv4-only

Example fix

// before
ParseIP("10.0.0.0/33", "")
// after
ParseIP("10.0.0.0/32", "")

func validCIDR(s string) bool {
	ip, _, err := net.ParseCIDR(s)
	return err == nil && ip.To4() != nil
}

hosts, err := parsers.ParseIP(host, "")
if err != nil {
	if strings.Contains(err.Error(), "parser_cidr_failed") {
		log.Fatalf("fix CIDR in %q: %v", host, err)
	}
	return err
}

When it happens

Trigger: parseHostString (called from ParseIP) encounters a token with '/' that net.ParseCIDR rejects — bad mask like '10.0.0.0/33', non-IP before the slash, or an IPv6 CIDR when only IPv4 is supported.

Common situations: Typos in netmasks, pasting 'host/path' strings accidentally, or using IPv6 CIDRs with an IPv4-only scanner.

Understand the failure class

Background: "Invalid ... format", "must be in format X", "does not look like a ..." — invalid argument format errors across CLI tools and libraries — this error's family across 17 libraries.

Related errors

• parser_ip_range_failed: %w
• parser_invalid_start_ip
• parser_invalid_end_ip
• parser_cidr_failed: %w
• parser_ipv4_only

AI-assisted analysis of shadow1ng/fscan@95cc12e753 (2026-09-06). Data as JSON: /api/errors/6655bdb59ca02649. Report an issue: GitHub.