Updated email processing.

- Added an option to enable smtp debugging via SMTP_DEBUG. This will
  trigger a trace of the smtp commands sent/received to/from the mail
server. Useful when troubleshooting.
- Added two options to ignore invalid certificates which either do not
  match at all, or only doesn't match the hostname.
- Updated lettre to the latest alpha.4 version.

.env.template

@@ -242,9 +242,9 @@
 # SMTP_HOST=smtp.domain.tld
 # SMTP_FROM=bitwarden-rs@domain.tld
 # SMTP_FROM_NAME=Bitwarden_RS
-# SMTP_PORT=587
+# SMTP_PORT=587          # Ports 587 (submission) and 25 (smtp) are standard without encryption and with encryption via STARTTLS (Explicit TLS). Port 465 is outdated and used with Implicit TLS.
-# SMTP_SSL=true          # (Explicit) - This variable by default configures Explicit STARTTLS, it will upgrade an insecure connection to a secure one. Unless SMTP_EXPLICIT_TLS is set to true.
+# SMTP_SSL=true          # (Explicit) - This variable by default configures Explicit STARTTLS, it will upgrade an insecure connection to a secure one. Unless SMTP_EXPLICIT_TLS is set to true. Either port 587 or 25 are default.
-# SMTP_EXPLICIT_TLS=true # (Implicit) - N.B. This variable configures Implicit TLS. It's currently mislabelled (see bug #851) - SMTP_SSL Needs to be set to true for this option to work.
+# SMTP_EXPLICIT_TLS=true # (Implicit) - N.B. This variable configures Implicit TLS. It's currently mislabelled (see bug #851) - SMTP_SSL Needs to be set to true for this option to work. Usually port 465 is used here.
 # SMTP_USERNAME=username
 # SMTP_PASSWORD=password
 # SMTP_TIMEOUT=15
@@ -259,6 +259,22 @@
 ## but might need to be changed in case it trips some anti-spam filters
 # HELO_NAME=
 
+## SMTP debugging
+## When set to true this will output very detailed SMTP messages.
+## WARNING: This could contain sensitive information like passwords and usernames! Only enable this during troubleshooting!
+# SMTP_DEBUG=false
+
+## Accept Invalid Hostnames
+## DANGEROUS: This option introduces significant vulnerabilities to man-in-the-middle attacks!
+## Only use this as a last resort if you are not able to use a valid certificate.
+# SMTP_ACCEPT_INVALID_HOSTNAMES=false
+
+## Accept Invalid Certificates
+## DANGEROUS: This option introduces significant vulnerabilities to man-in-the-middle attacks!
+## Only use this as a last resort if you are not able to use a valid certificate.
+## If the Certificate is valid but the hostname doesn't match, please use SMTP_ACCEPT_INVALID_HOSTNAMES instead.
+# SMTP_ACCEPT_INVALID_CERTS=false
+
 ## Require new device emails. When a user logs in an email is required to be sent.
 ## If sending the email fails the login attempt will fail!!
 # REQUIRE_DEVICE_EMAIL=false

Cargo.lock

@@ -33,12 +33,6 @@ dependencies = [
  "winapi 0.3.9",
 ]
 
-[[package]]
-name = "arrayvec"
-version = "0.5.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "23b62fc65de8e4e7f52534fb52b0f3ed04746ae267519eef2a83941e8085068b"
-
 [[package]]
 name = "atty"
 version = "0.2.14"
@@ -131,6 +125,18 @@ version = "1.2.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf1de2fe8c75bc145a2f577add951f8134889b4795d47466a54a5c846d691693"
 
+[[package]]
+name = "bitvec"
+version = "0.19.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a7ba35e9565969edb811639dbebfe34edc0368e472c5018474c8eb2543397f81"
+dependencies = [
+ "funty",
+ "radium",
+ "tap",
+ "wyz",
+]
+
 [[package]]
 name = "bitwarden_rs"
 version = "1.0.0"
@@ -638,6 +644,12 @@ version = "0.3.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3dcaa9ae7725d12cdb85b3ad99a434db70b468c09ded17e012d86b5c1010f7a7"
 
+[[package]]
+name = "funty"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ba62103ce691c2fd80fbae2213dfdda9ce60804973ac6b6e97de818ea7f52c8"
+
 [[package]]
 name = "futf"
 version = "0.1.4"
@@ -1144,9 +1156,9 @@ checksum = "830d08ce1d1d941e6b30645f1a0eb5643013d835ce3779a5fc208261dbe10f55"
 
 [[package]]
 name = "lettre"
-version = "0.10.0-alpha.3"
+version = "0.10.0-alpha.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "e422b6c03563bc47db09bb61a8ece4f1462de131455beb96c091e2998fa316a2"
+checksum = "dc8c2fc7873920aca23647e5e86d44ff3f40bbc5a5efaab445c9eb0e001c9f71"
 dependencies = [
  "base64 0.13.0",
  "hostname",
@@ -1160,22 +1172,10 @@ dependencies = [
  "rand 0.7.3",
  "regex",
  "serde",
+ "tracing",
  "uuid",
 ]
 
-[[package]]
-name = "lexical-core"
-version = "0.7.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "db65c6da02e61f55dae90a0ae427b2a5f6b3e8db09f58d10efab23af92592616"
-dependencies = [
- "arrayvec",
- "bitflags",
- "cfg-if 0.1.10",
- "ryu",
- "static_assertions",
-]
-
 [[package]]
 name = "libc"
 version = "0.2.80"
@@ -1448,11 +1448,11 @@ checksum = "72ef4a56884ca558e5ddb05a1d1e7e1bfd9a68d9ed024c21704cc98872dae1bb"
 
 [[package]]
 name = "nom"
-version = "5.1.2"
+version = "6.0.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ffb4262d26ed83a1c0a33a38fe2bb15797329c85770da05e6b828ddb782627af"
+checksum = "4489ccc7d668957ddf64af7cd027c081728903afa6479d35da7e99bf5728f75f"
 dependencies = [
- "lexical-core",
+ "bitvec",
  "memchr",
  "version_check 0.9.2",
 ]
@@ -1978,6 +1978,12 @@ dependencies = [
  "scheduled-thread-pool",
 ]
 
+[[package]]
+name = "radium"
+version = "0.5.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "941ba9d78d8e2f7ce474c015eea4d9c6d25b6a3327f9832ee29a4de27f91bbb8"
+
 [[package]]
 name = "rand"
 version = "0.4.6"
@@ -2617,12 +2623,6 @@ version = "0.4.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3015a7d0a5fd5105c91c3710d42f9ccf0abfb287d62206484dcc67f9569a6483"
 
-[[package]]
-name = "static_assertions"
-version = "1.1.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a2eb9349b6444b326872e140eb1cf5e7c522154d69e7a0ffb0fb81c06b37543f"
-
 [[package]]
 name = "stdweb"
 version = "0.4.20"
@@ -2782,6 +2782,12 @@ dependencies = [
  "time 0.1.44",
 ]
 
+[[package]]
+name = "tap"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "36474e732d1affd3a6ed582781b3683df3d0563714c59c39591e8ff707cf078e"
+
 [[package]]
 name = "tempfile"
 version = "3.1.0"
@@ -3371,6 +3377,12 @@ dependencies = [
  "winapi-build",
 ]
 
+[[package]]
+name = "wyz"
+version = "0.2.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "85e60b0d1b5f99db2556934e21937020776a5d31520bf169e851ac44e6420214"
+
 [[package]]
 name = "yansi"
 version = "0.5.0"

Cargo.toml

@@ -100,7 +100,7 @@ num-traits = "0.2.14"
 num-derive = "0.3.3"
 
 # Email libraries
-lettre = { version = "0.10.0-alpha.3", features = ["smtp-transport", "builder", "serde", "native-tls", "hostname"], default-features = false }
+lettre = { version = "0.10.0-alpha.4", features = ["smtp-transport", "builder", "serde", "native-tls", "hostname", "tracing"], default-features = false }
 newline-converter = "0.1.0"
 
 # Template library

src/config.rs

@@ -413,29 +413,35 @@ make_config! {
     /// SMTP Email Settings
     smtp: _enable_smtp {
         /// Enabled
-        _enable_smtp:           bool,   true,   def,     true;
+        _enable_smtp:                  bool,   true,   def,     true;
         /// Host
-        smtp_host:              String, true,   option;
+        smtp_host:                     String, true,   option;
         /// Enable Secure SMTP |> (Explicit) - Enabling this by default would use STARTTLS (Standard ports 587 or 25)
-        smtp_ssl:               bool,   true,   def,     true;
+        smtp_ssl:                      bool,   true,   def,     true;
         /// Force TLS |> (Implicit) - Enabling this would force the use of an SSL/TLS connection, instead of upgrading an insecure one with STARTTLS (Standard port 465)
-        smtp_explicit_tls:      bool,   true,   def,     false;
+        smtp_explicit_tls:             bool,   true,   def,     false;
         /// Port
-        smtp_port:              u16,    true,   auto,    |c| if c.smtp_explicit_tls {465} else if c.smtp_ssl {587} else {25};
+        smtp_port:                     u16,    true,   auto,    |c| if c.smtp_explicit_tls {465} else if c.smtp_ssl {587} else {25};
         /// From Address
-        smtp_from:              String, true,   def,     String::new();
+        smtp_from:                     String, true,   def,     String::new();
         /// From Name
-        smtp_from_name:         String, true,   def,     "Bitwarden_RS".to_string();
+        smtp_from_name:                String, true,   def,     "Bitwarden_RS".to_string();
         /// Username
-        smtp_username:          String, true,   option;
+        smtp_username:                 String, true,   option;
         /// Password
-        smtp_password:          Pass,   true,   option;
+        smtp_password:                 Pass,   true,   option;
         /// SMTP Auth mechanism |> Defaults for SSL is "Plain" and "Login" and nothing for Non-SSL connections. Possible values: ["Plain", "Login", "Xoauth2"]. Multiple options need to be separated by a comma ','.
-        smtp_auth_mechanism:    String, true,   option;
+        smtp_auth_mechanism:           String, true,   option;
         /// SMTP connection timeout |> Number of seconds when to stop trying to connect to the SMTP server
-        smtp_timeout:           u64,    true,   def,     15;
+        smtp_timeout:                  u64,    true,   def,     15;
         /// Server name sent during HELO |> By default this value should be is on the machine's hostname, but might need to be changed in case it trips some anti-spam filters
-        helo_name:              String, true,   option;
+        helo_name:                     String, true,   option;
+        /// Enable SMTP debugging (Know the risks!) |> DANGEROUS: Enabling this will output very detailed SMTP messages. This could contain sensitive information like passwords and usernames! Only enable this during troubleshooting!
+        smtp_debug:                    bool,   true,   def,     false;
+        /// Accept Invalid Certs (Know the risks!) |> DANGEROUS: Allow invalid certificates. This option introduces significant vulnerabilities to man-in-the-middle attacks!
+        smtp_accept_invalid_certs:     bool,   true,   def,     false;
+        /// Accept Invalid Hostnames (Know the risks!) |> DANGEROUS: Allow invalid hostnames. This option introduces significant vulnerabilities to man-in-the-middle attacks!
+        smtp_accept_invalid_hostnames: bool,   true,   def,     false;
     },
 
     /// Email 2FA Settings

src/mail.rs

@@ -7,6 +7,7 @@ use percent_encoding::{percent_encode, NON_ALPHANUMERIC};
 use lettre::{
     message::{header, Mailbox, Message, MultiPart, SinglePart},
     transport::smtp::authentication::{Credentials, Mechanism as SmtpAuthMechanism},
+    transport::smtp::client::{Tls, TlsParameters},
     transport::smtp::extension::ClientId,
     Address, SmtpTransport, Transport,
 };
@@ -22,21 +23,30 @@ fn mailer() -> SmtpTransport {
     use std::time::Duration;
     let host = CONFIG.smtp_host().unwrap();
 
-    // Determine security
+    let smtp_client = SmtpTransport::builder_dangerous(host.as_str())
-    let smtp_client = if CONFIG.smtp_ssl() {
-        if CONFIG.smtp_explicit_tls() {
-            SmtpTransport::relay(host.as_str())
-        } else {
-            SmtpTransport::starttls_relay(host.as_str())
-        }
-    } else {
-        Ok(SmtpTransport::builder_dangerous(host.as_str()))
-    };
-
-    let smtp_client = smtp_client.unwrap()
         .port(CONFIG.smtp_port())
         .timeout(Some(Duration::from_secs(CONFIG.smtp_timeout())));
 
+    // Determine security
+    let smtp_client = if CONFIG.smtp_ssl() {
+        let mut tls_parameters = TlsParameters::builder(host);
+        if CONFIG.smtp_accept_invalid_hostnames() {
+            tls_parameters.dangerous_accept_invalid_hostnames(true);
+        }
+        if CONFIG.smtp_accept_invalid_certs() {
+            tls_parameters.dangerous_accept_invalid_certs(true);
+        }
+        let tls_parameters = tls_parameters.build().unwrap();
+
+        if CONFIG.smtp_explicit_tls() {
+            smtp_client.tls(Tls::Wrapper(tls_parameters))
+        } else {
+            smtp_client.tls(Tls::Required(tls_parameters))
+        }
+    } else {
+        smtp_client
+    };
+
     let smtp_client = match (CONFIG.smtp_username(), CONFIG.smtp_password()) {
         (Some(user), Some(pass)) => smtp_client.credentials(Credentials::new(user, pass)),
         _ => smtp_client,
@@ -318,14 +328,17 @@ fn send_email(address: &str, subject: &str, body_html: &str, body_text: &str) ->
 
     // The boundary generated by Lettre it self is mostly too large based on the RFC822, so we generate one our selfs.
     use uuid::Uuid;
-    let boundary = format!("_Part_{}_", Uuid::new_v4().to_simple());
+    let unique_id = Uuid::new_v4().to_simple();
+    let boundary = format!("_Part_{}_", unique_id);
     let alternative = MultiPart::alternative().boundary(boundary).singlepart(text).singlepart(html);
+    let smtp_from = &CONFIG.smtp_from();
 
     let email = Message::builder()
+        .message_id(Some(format!("<{}.{}>", unique_id, smtp_from)))
         .to(Mailbox::new(None, Address::from_str(&address)?))
         .from(Mailbox::new(
             Some(CONFIG.smtp_from_name()),
-            Address::from_str(&CONFIG.smtp_from())?,
+            Address::from_str(smtp_from)?,
         ))
         .subject(subject)
         .multipart(alternative)?;

src/main.rs

@@ -115,6 +115,16 @@ fn init_logging(level: log::LevelFilter) -> Result<(), fern::InitError> {
         .level_for("rocket::fairing", log::LevelFilter::Off)
         .chain(std::io::stdout());
 
+    // Enable smtp debug logging only specifically for smtp when need.
+    // This can contain sensitive information we do not want in the default debug/trace logging.
+    if CONFIG.smtp_debug() {
+        println!("[WARNING] SMTP Debugging is enabled (SMTP_DEBUG=true). Sensitive information could be disclosed via logs!");
+        println!("[WARNING] Only enable SMTP_DEBUG during troubleshooting!\n");
+        logger = logger.level_for("lettre::transport::smtp", log::LevelFilter::Debug)
+    } else {
+        logger = logger.level_for("lettre::transport::smtp", log::LevelFilter::Off)
+    }
+
     if CONFIG.extended_logging() {
         logger = logger.format(|out, message, record| {
             out.finish(format_args!(