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Apply send cookies as a delta; judge NAT64/6to4 addresses by the IPv4 they carry

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This commit is contained in:
Gregory Schier
2026-08-17 09:39:57 -07:00
parent aa1d46a803
commit 212389cdf8
10 changed files with 219 additions and 23 deletions
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crates-server/yaak-send-proxy/README.md
+4 -1
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@@ -39,6 +39,7 @@ arguments; `--help` lists them all.
| `--allow-private-networks` | off | Let sends reach private, loopback and link-local addresses. **Off by default; see below.** |
| `--allow-hosts` | empty | Only these hosts (`api.example.com`, `*.example.com`). Empty means any host not denied. |
| `--deny-hosts` | empty | Never these hosts. Checked before the allow list. |
| `--nat64-prefixes` | empty | Network-specific NAT64 prefixes (`/96`) whose embedded IPv4 should be judged; the well-known and local-use prefixes always are. |
| `--max-request-bytes` | 16 MiB | Largest rendered request accepted from the tab. |
| `--max-response-bytes` | 64 MiB | Largest upstream body relayed before the send is cut off. |
| `--max-timeout-secs` | 60 | Ceiling on a send's timeout; a request asking for more (or none) gets this. |
@@ -55,7 +56,9 @@ sits on. So by default it refuses to connect to:
- loopback (`127/8`, `::1`), private (`10/8`, `172.16/12`, `192.168/16`,
`fc00::/7`), link-local (`169.254/16` — where cloud metadata lives — and
`fe80::/10`), carrier-grade NAT, multicast, reserved and unspecified ranges,
and IPv4 addresses tunnelled inside IPv6 forms (`::ffff:a.b.c.d`, NAT64);
and IPv4 addresses carried inside IPv6 forms (`::ffff:a.b.c.d`, the
well-known and local-use NAT64 prefixes, 6to4 — plus any NAT64 prefix you
name with `--nat64-prefixes`);
- anything not `http://` or `https://`.
The check runs **on the resolved addresses, after DNS**, for every hop of a
crates-server/yaak-send-proxy/src/config.rs
+7
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@@ -49,6 +49,13 @@ pub struct Config {
#[arg(long, env = "YAAK_PROXY_DENY_HOSTS", value_delimiter = ',')]
pub deny_hosts: Vec<String>,
/// NAT64 prefixes (/96) in use on this network, comma-separated, e.g. `2001:db8:64::`. The
/// well-known (64:ff9b::/96) and local-use (64:ff9b:1::/48) prefixes are always recognised;
/// a network-specific prefix has to be named here or an IPv6 address under it could reach
/// an internal IPv4 host through the translator.
#[arg(long, env = "YAAK_PROXY_NAT64_PREFIXES", value_delimiter = ',')]
pub nat64_prefixes: Vec<std::net::Ipv6Addr>,
/// Largest request the proxy accepts from the tab (the rendered request JSON, body included).
#[arg(long, env = "YAAK_PROXY_MAX_REQUEST_BYTES", default_value_t = 16 * 1024 * 1024)]
pub max_request_bytes: usize,
crates-server/yaak-send-proxy/src/guard.rs
+63 -12
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@@ -26,6 +26,9 @@ pub struct DestinationPolicy {
allow_private_networks: bool,
allow_hosts: Vec<HostPattern>,
deny_hosts: Vec<HostPattern>,
/// NAT64 prefixes (/96) in use on this network beyond the well-known ones. An IPv6
/// address under one of these is really an IPv4 destination, and is judged as that.
nat64_prefixes: Vec<Ipv6Addr>,
}
#[derive(Clone, Debug)]
@@ -60,11 +63,13 @@ impl DestinationPolicy {
allow_private_networks: bool,
allow_hosts: &[String],
deny_hosts: &[String],
nat64_prefixes: &[Ipv6Addr],
) -> Self {
Self {
allow_private_networks,
allow_hosts: allow_hosts.iter().filter_map(|h| HostPattern::parse(h)).collect(),
deny_hosts: deny_hosts.iter().filter_map(|h| HostPattern::parse(h)).collect(),
nat64_prefixes: nat64_prefixes.to_vec(),
}
}
@@ -105,6 +110,17 @@ impl DestinationPolicy {
if self.allow_private_networks {
return Ok(());
}
// An address under a configured NAT64 prefix reaches an IPv4 host; judge that host.
if let IpAddr::V6(v6) = ip
&& self.nat64_prefixes.iter().any(|p| p.segments()[..6] == v6.segments()[..6])
{
let v4 = trailing_v4(&v6);
if let Some(reason) = non_public_v4(v4) {
return Err(format!(
"Refusing to connect to {ip} (NAT64 for {v4}): {reason}. This proxy only sends to public addresses"
));
}
}
match non_public_reason(ip) {
Some(reason) => Err(format!(
"Refusing to connect to {ip}: {reason}. This proxy only sends to public addresses"
@@ -118,8 +134,10 @@ impl DestinationPolicy {
///
/// Every range here is one a hosted relay must never be talked into reaching: the machine
/// itself, the network it sits on, and the link-local range where cloud metadata services
/// (169.254.169.254) live. IPv4 addresses tunnelled inside IPv6 forms are unwrapped and judged
/// as IPv4, since that is what the socket would connect to.
/// (169.254.169.254) live. IPv4 addresses carried inside IPv6 forms — IPv4-mapped, the
/// well-known and local-use NAT64 prefixes, 6to4 — are unwrapped and judged as IPv4, since
/// that is where the packets end up. A network-specific NAT64 prefix is not knowable here;
/// see `--nat64-prefix`.
pub fn non_public_reason(ip: IpAddr) -> Option<&'static str> {
match ip {
IpAddr::V4(v4) => non_public_v4(v4),
@@ -127,7 +145,7 @@ pub fn non_public_reason(ip: IpAddr) -> Option<&'static str> {
if let Some(v4) = v6.to_ipv4_mapped() {
return non_public_v4(v4);
}
if let Some(v4) = nat64_embedded_v4(&v6) {
if let Some(v4) = embedded_v4(&v6) {
return non_public_v4(v4);
}
if v6.is_loopback() {
@@ -180,15 +198,33 @@ fn non_public_v4(v4: Ipv4Addr) -> Option<&'static str> {
}
}
/// The IPv4 address inside a NAT64 (64:ff9b::/96) address, if this is one.
fn nat64_embedded_v4(v6: &Ipv6Addr) -> Option<Ipv4Addr> {
/// The IPv4 address an IPv6 address stands for, when it is one of the standard translation
/// forms: NAT64 well-known prefix (64:ff9b::/96), NAT64 local-use prefix (64:ff9b:1::/48,
/// RFC 8215), or 6to4 (2002::/16, where the IPv4 sits in the next 32 bits).
fn embedded_v4(v6: &Ipv6Addr) -> Option<Ipv4Addr> {
let s = v6.segments();
if s[0] == 0x64 && s[1] == 0xff9b && s[2..6].iter().all(|x| *x == 0) {
let o = v6.octets();
Some(Ipv4Addr::new(o[12], o[13], o[14], o[15]))
} else {
None
return Some(trailing_v4(v6));
}
if s[0] == 0x64 && s[1] == 0xff9b && s[2] == 1 {
return Some(trailing_v4(v6));
}
if s[0] == 0x2002 {
return Some(Ipv4Addr::new(
(s[1] >> 8) as u8,
(s[1] & 0xff) as u8,
(s[2] >> 8) as u8,
(s[2] & 0xff) as u8,
));
}
None
}
/// The last 32 bits of an IPv6 address as an IPv4 address (where every /96 NAT64 prefix
/// keeps it).
fn trailing_v4(v6: &Ipv6Addr) -> Ipv4Addr {
let o = v6.octets();
Ipv4Addr::new(o[12], o[13], o[14], o[15])
}
/// An [`HttpSender`] that checks each hop's URL against the policy before delegating.
@@ -273,12 +309,26 @@ mod tests {
}
}
#[test]
fn a_configured_nat64_prefix_is_judged_by_the_address_it_carries() {
// A made-up global prefix, standing in for whatever the network's translator uses
let prefix: Ipv6Addr = "2a02:1234:64::".parse().unwrap();
let policy = DestinationPolicy::new(false, &[], &[], &[prefix]);
assert!(policy.check_ip(ip("2a02:1234:64::a9fe:a9fe")).is_err(), "metadata behind NAT64");
assert!(policy.check_ip(ip("2a02:1234:64::0a00:1")).is_err(), "10.0.0.1 behind NAT64");
assert!(policy.check_ip(ip("2a02:1234:64::0101:0101")).is_ok(), "1.1.1.1 behind NAT64");
// Without the prefix configured the same address is an ordinary global v6, and passes:
// that is exactly the gap the option exists to close.
let policy = DestinationPolicy::new(false, &[], &[], &[]);
assert!(policy.check_ip(ip("2a02:1234:64::a9fe:a9fe")).is_ok());
}
#[test]
fn private_networks_can_be_opted_in() {
let policy = DestinationPolicy::new(true, &[], &[]);
let policy = DestinationPolicy::new(true, &[], &[], &[]);
assert!(policy.check_url("http://127.0.0.1/").is_ok());
assert!(policy.check_url("http://169.254.169.254/").is_ok());
let policy = DestinationPolicy::new(false, &[], &[]);
let policy = DestinationPolicy::new(false, &[], &[], &[]);
assert!(policy.check_url("http://127.0.0.1/").is_err());
assert!(policy.check_url("http://[::1]/").is_err());
assert!(policy.check_url("http://169.254.169.254/latest/meta-data").is_err());
@@ -290,6 +340,7 @@ mod tests {
false,
&["*.example.com".into(), "api.test".into()],
&["bad.example.com".into()],
&[],
);
assert!(policy.check_url("https://example.com/").is_ok());
assert!(policy.check_url("https://a.b.example.com/").is_ok());
@@ -302,7 +353,7 @@ mod tests {
#[test]
fn only_http_schemes() {
let policy = DestinationPolicy::new(true, &[], &[]);
let policy = DestinationPolicy::new(true, &[], &[], &[]);
assert!(policy.check_url("ftp://example.com/").is_err());
assert!(policy.check_url("file:///etc/passwd").is_err());
assert!(policy.check_url("https://example.com/").is_ok());
crates-server/yaak-send-proxy/src/main.rs
+1
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@@ -53,6 +53,7 @@ async fn main() {
config.allow_private_networks,
&config.allow_hosts,
&config.deny_hosts,
&config.nat64_prefixes,
);
let state = AppState {
limits: Arc::new(SendLimits {