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fix: reject invalid dotted-decimal in hostname_rfc1123 validation #1562

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fix: reject invalid dotted-decimal in hostname_rfc1123 validation #1562

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976136e
fix: reject invalid dotted-decimal in hostname_rfc1123 validation
Apr 15, 2026
5df2fdd
fix: narrow dotted decimal hostname check
Herrtian May 22, 2026
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32 changes: 31 additions & 1 deletion baked_in.go
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Original file line number Diff line number Diff line change
Expand Up @@ -2798,8 +2798,38 @@ func isHostnameRFC952(fl FieldLevel) bool {
return hostnameRegexRFC952().MatchString(fl.Field().String())
}

func isDottedDecimalIPv4(s string) bool {
labels := 1
labelLen := 0

for _, c := range s {
switch {
case c == '.':
if labelLen == 0 {
return false
}
labels++
labelLen = 0
case c >= '0' && c <= '9':
labelLen++
default:
return false
}
}

return labels == 4 && labelLen > 0
}

func isHostnameRFC1123(fl FieldLevel) bool {
return hostnameRegexRFC1123().MatchString(fl.Field().String())
val := fl.Field().String()
if !hostnameRegexRFC1123().MatchString(val) {
return false
}
if isDottedDecimalIPv4(val) {
ip := net.ParseIP(val)
return ip != nil && ip.To4() != nil
}
return true
}

func isFQDN(fl FieldLevel) bool {
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7 changes: 7 additions & 0 deletions validator_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -10677,6 +10677,13 @@ func TestHostnameRFC1123Validation(t *testing.T) {
{"example.", false},
{"test_example", false},
{"192.168.0.1", true},
{"0.0.0.0", true},
{"255.255.255.255", true},
{"277.168.0.1", false},
{"192.168.0.256", false},
{"192.168.0.a", true},
{"123.456", true},
{"1.2.3", true},
{"email@example.com", false},
{"2001:cdba:0000:0000:0000:0000:3257:9652", false},
{"2001:cdba:0:0:0:0:3257:9652", false},
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