OASIS Mailing List ArchivesView the OASIS mailing list archive below
or browse/search using MarkMail.


Help: OASIS Mailing Lists Help | MarkMail Help

mqtt message

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]

Subject: [OASIS Issue Tracker] (MQTT-505) Denial of Service Attacks possible

Dominik Obermaier created MQTT-505:

             Summary: Denial of Service Attacks possible 
                 Key: MQTT-505
                 URL: https://issues.oasis-open.org/browse/MQTT-505
             Project: OASIS Message Queuing Telemetry Transport (MQTT) TC
          Issue Type: Bug
    Affects Versions: 5, CSD01
            Reporter: Dominik Obermaier

The current state of the MQTT 5 specification states:

Clients are allowed to send further MQTT Control Packets immediately after sending a CONNECT packet; Clients need not wait (sic!) for a CONNACK packet to arrive from the Server. If the Server rejects the CONNECT, it MUST NOT process any data sent by the Client after the CONNECT packet except AUTH packets.

This behavior may be used for Denial of Service attacks. Consider the following scenario:

1. A malicious client connects to the Broker and sends an invalid CONNECT packet
2. The server has a complex authentication mechanism and it may take up to several seconds (or even longer!) until the validity of the CONNECT can be determined
3. The malicious client bombards the server with PUBLISH packets
4. The broker must queue all these messages until the CONNECT returns. The broker implementation *can't* stop to read from the socket (and thus apply TCP backpressure to the client) since an AUTH packet could be sent by the client.

MQTT 3.1.1 also allowed unauthenticated clients to send data, the broker implementation could stop to read from the socket until the CONNACK packet is produced.

To solve the issue, a proposal could be: 

The Server MAY discard any packets sent by the Client prior to a successful authentication.

A non-normative comment could be added, that a broker may decide to use a bounded queue for "holding back" the data. If the queue is full, the PUBLISH messages (or other packets) could be dropped and an error code "0x97 - Quota exceeded" could be included in the ACK (e.g. PUBACK, ...). 

A slightly better approach to fix this problem would be to disallow the sending of any packets before all AUTH packets are exchanged.

This message was sent by Atlassian JIRA

[Date Prev] | [Thread Prev] | [Thread Next] | [Date Next] -- [Date Index] | [Thread Index] | [List Home]