= Security checklist
:navtitle: Security checklist

This document aims as summarizing threats, security best practices as well as recommendations.

== Threats

Operating an email server exposes you to the following threats:

 - Spammers might attempt to use your servers to send their spam messages on their behalf. We speak of
*open relay*. In addition to the resources consumed being an open relay will affect the trust other mail
installations have in you, and thus will cause legitimate traffic to be rejected.
 - Emails mostly consist of private data, which shall only be accessed by their legitimate user. Failure
to do so might result in *information disclosure*.
 - *Email forgery*. An attacker might craft an email on the behalf of legitimate users.
 - Email protocols allow user to authenticate and thus can be used as *oracles* to guess user passwords.
 - *Spam*. Non legitimate traffic can be a real burden to your users.
 - *Denial of service*: A small request may result in a very large response and require considerable work on the server...
 - *Denial of service*: A malicious JMAP client may use the JMAP push subscription to attempt to flood a third party
server with requests, creating a denial-of-service attack and masking the attacker’s true identity.

== Best practices

The following sections ranks best practices.

=== Best practices: Must

 - 1. Configure James in order not to be an xref:configure/smtp.adoc#_about_open_relays[open relay]. This should be the
case with the default configuration.

Be sure in xref:configure/smtp.adoc[smtpserver.xml] to activate the following options: `verifyIdentity`.

We then recommend to manually test your installation in order to ensure that:

    - Unauthenticated SMTP users cannot send mails to external email addresses (they are not relayed)
    - Unauthenticated SMTP users can send mails to internal email addresses
    - Unauthenticated SMTP users cannot use local addresses in their mail from, and send emails both locally and to distant targets.

 - 2. Avoid *STARTTLS* usage and favor SSL. Upgrade from a non encrypted channel into an encrypted channel is an opportunity
for additional vulnerabilities. This is easily prevented by requiring SSL connection upfront. link:https://nostarttls.secvuln.info/[Read more...]

Please note that STARTTLS is still beneficial in the context of email relaying, which happens on SMTP port 25 unencrypted,
and enable opportunistic encryption upgrades that would not overwise be possible. We recommend keeping STARTTLS activated
for SMTP port 25.

 - 3. Use SSL for xref:configure/mailets.adoc#_remotedelivery[remote delivery] whenever you are using a gateway relaying SMTP server.

 - 4. Rely on an external identity service, dedicated to user credential storage. James supports xref:configure/usersrepository.adoc#_configuring_a_ldap[LDAP]. If you are
forced to store users in James be sure to choose `PBKDF2` as a hashing algorithm. Also, delays on authentication failures
are supported via the `verifyFailureDelay` property. Note that IMAP / SMTP connections are closed after 3 authentication
failures.

 - 5. Ensure that xref:configure/webadmin.adoc[WebAdmin] is not exposed unencrypted to the outer world. Doing so trivially
exposes yourself. You can either disable it, activate JWT security, or restrict it to listen only on localhost.

 - 6. Set up `HTTPS` for http based protocols, namely *JMAP* and *WebAdmin*. We recommend the use of a reverse proxy like Nginx.

 - 7. Set up link:https://james.apache.org/howTo/spf.html[SPF] and link:https://james.apache.org/howTo/dkim.html[DKIM]
for your outgoing emails to be trusted.

 - 8. Prevent access to JMX. This can be achieved through a strict firewalling policy
(link:https://nickbloor.co.uk/2017/10/22/analysis-of-cve-2017-12628/[blocking port 9999 is not enough])
or xref:configure/jmx.adoc[disabling JMX]. JMX is needed to use the existing CLI application but webadmin do offer similar
features.

 - 9. If JMAP is enabled, be sure that JMAP PUSH cannot be used for server side request forgery. This can be
xref:configure/jmap.adoc[configured] using the `push.prevent.server.side.request.forgery=true` property,
forbidding push to private addresses.

=== Best practice: Should

 - 1. Avoid advertising login/authenticate capabilities in clear channels. This might prevent some clients to attempt login
on clear channels, and can be configured for both xref:configure/smtp.adoc[SMTP] and xref:configure/imap.adoc[IMAP]
using `auth.plainAuthEnabled=false`.

 - 2. Verify link:https://james.apache.org/howTo/spf.html[SPF] and xref:configure/mailets.adoc#_dkimverify[DKIM] for your incoming emails.

 - 3. Set up reasonable xref:operate/webadmin.adoc#_administrating_quotas[storage quota] for your users.

 - 4. We recommend setting up anti-spam and anti-virus solutions. James comes with some xref:configure/spam.adoc[SpamAssassin]
integration, and some experimental, insufficiently tested xref:configure/mailets.adoc#_clamavscan[ClamAV] tooling exisits.
Filtering with third party systems upstream is also possible.

 - 5. In order to limit your attack surface, disable protocols you or your users do not use. This includes the JMAP protocol,
POP3, ManagedSieve, etc... Be conservative on what you expose.

=== Best practice: Could

 - 1. Set up link:https://openid.net/connect/[OIDC] for IMAP, SMTP and JMAP. Disable login/plain/basic authentication.

 - 2. You can configure xref:configure/ssl.adoc#_client_authentication_via_certificates[Client authentication via certificates].

 - 3. You can xref:configure/mailets.adoc#_smimesign[sign], xref:configure/mailets.adoc#_smimechecksignature[verify]
and xref:configure/mailets.adoc#_smimedecrypt[decrypt] your email traffic using link:https://datatracker.ietf.org/doc/html/rfc5751[SMIME].

== Known vulnerabilities

Several vulnerabilities have had been reported for previous releases of Apache James server.

Be sure not to run those! We highly recommend running the latest release, which we put great effort in not to use
outdated dependencies.

=== Reporting vulnerabilities

We follow the standard procedures within the ASF regarding link:https://apache.org/security/committers.html#vulnerability-handling[vulnerability handling]

=== CVE-2021-38542: Apache James vulnerable to STARTTLS command injection (IMAP and POP3)

Apache James prior to release 3.6.1 is vulnerable to a buffering attack relying on the use of the STARTTLS
command. This can result in Man-in -the-middle command injection attacks, leading potentially to leakage
of sensible information.

*Severity*: Moderate

This issue is being tracked as link:https://issues.apache.org/jira/browse/JAMES-1862[JAMES-1862]

*Mitigation*: We recommend upgrading to Apache James 3.6.1, which fixes this vulnerability.

Furthermore, we recommend, if possible to dis-activate STARTTLS and rely solely on explicit TLS for mail protocols, including SMTP, IMAP and POP3.

Read more link:https://nostarttls.secvuln.info/[about STARTTLS security here].

=== CVE-2021-40110: Apache James IMAP vulnerable to a ReDoS

Using Jazzer fuzzer, we identified that an IMAP user can craft IMAP LIST commands to orchestrate a Denial
Of Service using a vulnerable Regular expression. This affected Apache James prior to 3.6.1

*Severity*: Moderate

This issue is being tracked as link:https://issues.apache.org/jira/browse/JAMES-3635[JAMES-3635]

*Mitigation*: We recommend upgrading to Apache James 3.6.1, which enforce the use of RE2J regular
expression engine to execute regex in linear time without back-tracking.

=== CVE-2021-40111: Apache James IMAP parsing Denial Of Service

While fuzzing with Jazzer the IMAP parsing stack we discover that crafted APPEND and STATUS IMAP command
could be used to trigger infinite loops resulting in expensive CPU computations and OutOfMemory exceptions.
This can be used for a Denial Of Service attack. The IMAP user needs to be authenticated to exploit this
vulnerability. This affected Apache James prior to version 3.6.1.

*Severity*: Moderate

This issue is being tracked as link:https://issues.apache.org/jira/browse/JAMES-3634[JAMES-3634]

*Mitigation*: We recommend upgrading to Apache James 3.6.1, which fixes this vulnerability.

=== CVE-2021-40525: Apache James: Sieve file storage vulnerable to path traversal attacks

Apache James ManagedSieve implementation alongside with the file storage for sieve scripts is vulnerable
to path traversal, allowing reading and writing any file.

*Severity*: Moderate

This issue is being tracked as link:https://issues.apache.org/jira/browse/JAMES-3646[JAMES-3646]

*Mitigation*:This vulnerability had been patched in Apache James 3.6.1 and higher. We recommend the upgrade.

This could also be mitigated by ensuring manageSieve is disabled, which is the case by default.

Distributed and Cassandra based products are also not impacted.

=== CVE-2017-12628 Privilege escalation using JMX

The Apache James Server prior version 3.0.1 is vulnerable to Java deserialization issues.
One can use this for privilege escalation.
This issue can be mitigated by:

 - Upgrading to James 3.0.1 onward
 - Using a recent JRE (Exploit could not be reproduced on OpenJdk 8 u141)
 - Exposing JMX socket only to localhost (default behaviour)
 - Possibly running James in a container
 - Disabling JMX all-together (Guice only)

Read more link:http://james.apache.org//james/update/2017/10/20/james-3.0.1.html[here].