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Reject private and loopback IPs in checkMetadataURL #21

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Merged
andrew merged 1 commit into from
May 2, 2026
Merged

Reject private and loopback IPs in checkMetadataURL #21

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19 changes: 18 additions & 1 deletion fetch/resolver.go
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@ import (
"context"
"errors"
"fmt"
"net"
"net/url"
"strings"
"unicode"
Expand Down Expand Up @@ -183,12 +184,28 @@ func checkMetadataURL(raw string) error {
if u.Scheme != "https" {
return fmt.Errorf("%w: scheme %q", ErrUnsafeURL, u.Scheme)
}
if u.Hostname() == "" {
hostname := u.Hostname()
if hostname == "" {
return fmt.Errorf("%w: empty host", ErrUnsafeURL)
}
if isPrivateHost(hostname) {
return fmt.Errorf("%w: private/loopback host %q", ErrUnsafeURL, hostname)
}
return nil
}

func isPrivateHost(hostname string) bool {
ip := net.ParseIP(hostname)
if ip == nil {
ips, err := net.LookupIP(hostname)
if err != nil || len(ips) == 0 {
return false
}
ip = ips[0]
}
return ip.IsLoopback() || ip.IsPrivate() || ip.IsLinkLocalUnicast() || ip.IsLinkLocalMulticast()
}

func filenameFromURL(url string) string {
if idx := strings.LastIndex(url, "/"); idx >= 0 {
return url[idx+1:]
Expand Down
3 changes: 3 additions & 0 deletions fetch/resolver_test.go
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Original file line number Diff line number Diff line change
Expand Up @@ -141,6 +141,9 @@ func TestCheckMetadataURL(t *testing.T) {
{"https:///path/only", false},
{"//169.254.169.254/latest/meta-data/", false},
{"169.254.169.254/latest/meta-data/", false},
{"https://169.254.169.254/latest/meta-data/", false},
{"https://127.0.0.1/something", false},
{"https://[::1]/something", false},
{"", false},
{"\x00https://evil", false},
}
Expand Down