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Documentation and changes for `verify_server_hostname` (#5069) 

* verify_server_hostname implies verify_outgoing

* mention CVE in the docs.
This commit is contained in:
Jack Pearkes 2018-12-06 13:51:49 -08:00 committed by GitHub
parent 18d2269ca2
commit 9d170164e4
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GPG Key ID: 4AEE18F83AFDEB23
6 changed files with 86 additions and 22 deletions
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16
agent/config/builder.go
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@ -613,6 +613,18 @@ func (b *Builder) Build() (rt RuntimeConfig, err error) {
enableRemoteScriptChecks := b.boolVal(c.EnableScriptChecks)
enableLocalScriptChecks := b.boolValWithDefault(c.EnableLocalScriptChecks, enableRemoteScriptChecks)
// VerifyServerHostname implies VerifyOutgoing
verifyServerName := b.boolVal(c.VerifyServerHostname)
verifyOutgoing := b.boolVal(c.VerifyOutgoing)
if verifyServerName {
// Setting only verify_server_hostname is documented to imply
// verify_outgoing. If it doesn't then we risk sending communication over TCP
// when we documented it as forcing TLS for RPCs. Enforce this here rather
// than in several different places through the code that need to reason
// about it. (See CVE-2018-19653)
verifyOutgoing = true
}
// ----------------------------------------------------------------
// build runtime config
//
@ -840,8 +852,8 @@ func (b *Builder) Build() (rt RuntimeConfig, err error) {
VerifyIncoming: b.boolVal(c.VerifyIncoming),
VerifyIncomingHTTPS: b.boolVal(c.VerifyIncomingHTTPS),
VerifyIncomingRPC: b.boolVal(c.VerifyIncomingRPC),
VerifyOutgoing: b.boolVal(c.VerifyOutgoing),
VerifyServerHostname: b.boolVal(c.VerifyServerHostname),
VerifyOutgoing: verifyOutgoing,
VerifyServerHostname: verifyServerName,
Watches: c.Watches,
}

18
agent/config/runtime_test.go
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@ -2619,6 +2619,24 @@ func TestConfigFlagsAndEdgecases(t *testing.T) {
}
},
},
{
// This tests checks that VerifyServerHostname implies VerifyOutgoing
desc: "verify_server_hostname implies verify_outgoing",
args: []string{
`-data-dir=` + dataDir,
},
json: []string{`{
"verify_server_hostname": true
}`},
hcl: []string{`
verify_server_hostname = true
`},
patch: func(rt *RuntimeConfig) {
rt.DataDir = dataDir
rt.VerifyServerHostname = true
rt.VerifyOutgoing = true
},
},
}
testConfig(t, tests, dataDir)

4
tlsutil/config.go
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@ -125,10 +125,6 @@ func (c *Config) KeyPair() (*tls.Certificate, error) {
// requests. It will return a nil config if this configuration should
// not use TLS for outgoing connections.
func (c *Config) OutgoingTLSConfig() (*tls.Config, error) {
// If VerifyServerHostname is true, that implies VerifyOutgoing
if c.VerifyServerHostname {
c.VerifyOutgoing = true
}
if !c.UseTLS && !c.VerifyOutgoing {
return nil, nil
}

4
tlsutil/config_test.go
View File

@ -153,6 +153,7 @@ func TestConfig_OutgoingTLS_ServerName(t *testing.T) {
func TestConfig_OutgoingTLS_VerifyHostname(t *testing.T) {
conf := &Config{
VerifyOutgoing: true,
VerifyServerHostname: true,
CAFile: "../test/ca/root.cer",
}
@ -263,6 +264,7 @@ func TestConfig_outgoingWrapper_OK(t *testing.T) {
CertFile: "../test/hostname/Alice.crt",
KeyFile: "../test/hostname/Alice.key",
VerifyServerHostname: true,
VerifyOutgoing: true,
Domain: "consul",
}
@ -297,6 +299,7 @@ func TestConfig_outgoingWrapper_BadDC(t *testing.T) {
CertFile: "../test/hostname/Alice.crt",
KeyFile: "../test/hostname/Alice.key",
VerifyServerHostname: true,
VerifyOutgoing: true,
Domain: "consul",
}
@ -329,6 +332,7 @@ func TestConfig_outgoingWrapper_BadCert(t *testing.T) {
CertFile: "../test/key/ourdomain.cer",
KeyFile: "../test/key/ourdomain.key",
VerifyServerHostname: true,
VerifyOutgoing: true,
Domain: "consul",
}

32
website/source/docs/agent/options.html.md
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@ -1595,19 +1595,35 @@ default will automatically work with some tooling.
default, HTTPS is disabled.
* <a name="verify_outgoing"></a><a href="#verify_outgoing">`verify_outgoing`</a> - If set to
true, Consul requires that all outgoing connections
true, Consul requires that all outgoing connections from this agent
make use of TLS and that the server provides a certificate that is signed by
a Certificate Authority from the [`ca_file`](#ca_file) or [`ca_path`](#ca_path). By default,
this is false, and Consul will not make use of TLS for outgoing connections. This applies to clients
and servers as both will make outgoing connections.
* <a name="verify_server_hostname"></a><a href="#verify_server_hostname">`verify_server_hostname`</a> - If set to
true, Consul verifies for all outgoing connections that the TLS certificate presented by the servers
matches "server.&lt;datacenter&gt;.&lt;domain&gt;" hostname. This implies `verify_outgoing`.
By default, this is false, and Consul does not verify the hostname of the certificate, only
that it is signed by a trusted CA. This setting is important to prevent a compromised
client from being restarted as a server, and thus being able to perform a MITM attack
or to be added as a Raft peer. This is new in 0.5.1.
~> **Security Note:** Note that servers that specify `verify_outgoing =
true` will always talk to other servers over TLS, but they still _accept_
non-TLS connections to allow for a transition of all clients to TLS.
Currently the only way to enforce that no client can communicate with a
server unencrypted is to also enable `verify_incoming` which requires client
certificates too.
* <a name="verify_server_hostname"></a><a
href="#verify_server_hostname">`verify_server_hostname`</a> - If set to true,
Consul verifies for all outgoing TLS connections that the TLS certificate
presented by the servers matches "server.&lt;datacenter&gt;.&lt;domain&gt;"
hostname. By default, this is false, and Consul does not verify the hostname
of the certificate, only that it is signed by a trusted CA. This setting is
_critical_ to prevent a compromised client from being restarted as a server
and having all cluster state _including all ACL tokens and Connect CA root keys_
replicated to it. This is new in 0.5.1.
~> **Security Note:** From versions 0.5.1 to 1.4.0, due to a bug, setting
this flag alone _does not_ imply `verify_outgoing` and leaves client to server
and server to server RPCs unencrypted despite the documentation stating otherwise. See
[CVE-2018-19653](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-19653)
for more details. For those versions you **must also set `verify_outgoing =
true`** to ensure encrypted RPC connections.
* <a name="watches"></a><a href="#watches">`watches`</a> - Watches is a list of watch
specifications which allow an external process to be automatically invoked when a

26
website/source/docs/internals/security.html.md
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@ -47,10 +47,21 @@ items outside of Consul's threat model as noted in sections below.
* **Encryption enabled.** TCP and UDP encryption must be enabled and configured
to prevent plaintext communication between Consul agents. At a minimum,
verify_outgoing should be enabled to verify server authenticity with each
server having a unique TLS certificate. verify_incoming provides additional
agent verification, but shouldn't directly affect the threat model since
requests must also contain a valid ACL token.
`verify_outgoing` should be enabled to verify server authenticity with each
server having a unique TLS certificate. `verify_server_hostname` is also
required to prevent a compromised agent restarting as a server and being given
access to all secrets.
`verify_incoming` provides additional agent verification via mutual
authentication, but isn't _strictly_ necessary to enforce the threat model
since requests must also contain a valid ACL token. The subtlety is that
currently `verify_incoming = false` will allow servers to still accept
un-encrypted connections from clients (to allow for gradual TLS rollout). That
alone doesn't violate the threat model, but any misconfigured client that
chooses not to use TLS will violate the model. We recommend setting this to
true. If it is left as false care must be taken to ensure all consul clients
use `verify_outgoing = true` as noted above, but also all external API/UI
access must be via HTTPS with HTTP listeners disabled.
### Known Insecure Configurations
@ -74,6 +85,13 @@ non-default options that potentially present additional security risks.
ACLs restrict access, for example any management token grants access to
execute arbitrary code on the cluster.
* **Verify Server Hostname Used Alone.** From version 0.5.1 to 1.4.0 we documented that
`verify_server_hostname` being `true` _implied_ `verify_outgoing` however due
to a bug this was not the case so setting _only_ `verify_server_hostname`
results in plaintext communciation between client and server. See
[CVE-2018-19653](https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2018-19653)
for more details. This is fixed in 1.4.1.
## Threat Model
The following are parts of the Consul threat model: