Private / Reserved IPv4 Ranges Regex for Go
/^(?:10\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|172\.(?:1[6-9]|2[0-9]|3[01])\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|192\.168\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|127\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|169\.254\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))$/What this pattern does
This page provides a comprehensive, battle-tested regular expression for matching private / reserved ipv4 ranges, ported and verified for Go. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. The snippet below is ready to drop into your Go project — whether you're validating in a Gin handler, a gRPC service, or a command-line tool.
Go Implementation
// Private / Reserved IPv4 Ranges
// ReDoS-safe | RegexVault — Security > Network Security
package validation
import "regexp"
var privateReservedIpv4RangesRe = regexp.MustCompile(`^(?:10\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|172\.(?:1[6-9]|2[0-9]|3[01])\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|192\.168\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|127\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)|169\.254\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?))$`)
func ValidatePrivateReservedIpv4Ranges(s string) bool {
return privateReservedIpv4RangesRe.MatchString(s)
}
// Example
// fmt.Println(ValidatePrivateReservedIpv4Ranges("10.0.0.1")) // trueTest Cases
Matches (Valid) | Rejects (Invalid) |
|---|---|
10.0.0.1 | 8.8.8.8 |
172.16.0.1 | 1.1.1.1 |
192.168.1.1 | 172.15.0.1 |
127.0.0.1 | 172.32.0.1 |
169.254.0.1 | 11.0.0.1 |
When to use this pattern
This pattern is drawn from the Security > Network Security category and carries a ReDoS-safe certification. That matters for Go developers because Go's RE2 engine is inherently safe from catastrophic backtracking, but this pattern has been additionally verified for correctness. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.
Common Pitfalls
SSRF (Server-Side Request Forgery) attacks often use private IP addresses to reach internal services. Additional ranges to block: 0.0.0.0/8 (current network), 100.64.0.0/10 (shared address space), 240.0.0.0/4 (reserved). Also handle IPv6 equivalents.
Technical Notes
Private ranges: 10.0.0.0/8 (Class A, RFC 1918), 172.16.0.0/12 (Class B, RFC 1918), 192.168.0.0/16 (Class C, RFC 1918), 127.0.0.0/8 (loopback), 169.254.0.0/16 (link-local APIPA). Use for SSRF protection: reject private IPs in user-supplied URLs.
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