shadow1ng/fscan · error

parser_cidr_failed: %w

Error message

parser_cidr_failed: %w

What it means

newHostSource fails when a host expression containing '/' looks like a CIDR but newCIDRHostSource cannot parse it, wrapping the parse error with an i18n message. It indicates malformed CIDR notation in the target specification.

Source

Thrown at common/parsers/host_iterator.go:307

			return nil, err
		}
		sources = append(sources, src)
	}
	return sources, nil
}

func newHostSource(host string) (hostSource, error) {
	switch {
	case host == "192":
		return newCIDRHostSource("192.168.0.0/16")
	case host == "172":
		return newCIDRHostSource("172.16.0.0/12")
	case host == "10":
		return newCIDRHostSource("10.0.0.0/8")
	case strings.Contains(host, "/"):
		src, err := newCIDRHostSource(host)
		if err != nil {
			return nil, fmt.Errorf(i18n.Tr("parser_cidr_failed", host)+": %w", err)
		}
		return src, nil
	case strings.Contains(host, "-") && !strings.Contains(host, ":") && looksLikeIPRange(host):
		src, err := newRangeHostSource(host)
		if err != nil {
			return nil, fmt.Errorf(i18n.Tr("parser_ip_range_failed", host)+": %w", err)
		}
		return src, nil
	default:
		return &singleHostSource{host: host}, nil
	}
}

func newCIDRHostSource(cidr string) (hostSource, error) {
	_, ipNet, err := net.ParseCIDR(cidr)
	if err != nil {
		return nil, err
	}

View on GitHub (pinned to 95cc12e753)

Solutions

1. Correct the CIDR notation (valid base IP and prefix 0-32)
2. Validate CIDR strings with net.ParseCIDR before passing them
3. Split multiple targets and test each individually to locate the bad one

Example fix

// before
targets := []string{"192.168.1.0/33"}
// after
for _, t := range targets {
    if _, _, err := net.ParseCIDR(t); err != nil { log.Fatalf("bad CIDR %s: %v", t, err) }
}

if strings.Contains(target, "/") {
    if _, _, err := net.ParseCIDR(target); err != nil {
        return fmt.Errorf("invalid CIDR %q: %w", target, err)
    }
}

srcs, err := newHostSources(targets)
if err != nil {
    if strings.Contains(err.Error(), "parser_cidr_failed") {
        log.Fatalf("fix CIDR notation: %v", err)
    }
}

When it happens

Trigger: Passing targets like '192.168.1.0/33', 'abc/24', or '192.168.1.0/xx' where the prefix length or base address is invalid.

Common situations: Hand-written target lists with typos; copied CIDR with wrong prefix length; variable interpolation producing 'prefix/24' garbage.

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_ip_end_val
• parser_invalid_ip_range_val
• portfinger_probe_name_invalid
• Parse error: first line must start with "Probe " or "Exclude

AI-assisted analysis of shadow1ng/fscan@95cc12e753 (2026-09-06). Data as JSON: /api/errors/4fb422b2bcbb2784. Report an issue: GitHub.