CVE-2020-13849
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedThe MQTT protocol 3.1.1 requires a server to set a timeout value of 1.5 times the Keep-Alive value specified by a client, which allows remote attackers to cause a denial of service (loss of the ability to establish new connections), as demonstrated by SlowITe.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceThe MQTT 3.1.1 specification requires servers to set connection timeouts to 1.5x the Keep-Alive value specified by the client. Attackers can exploit this by initiating connections with very large Keep-Alive values, causing the server to hold connection resources for extended periods and eventually exhaust its capacity to accept new connections, as demonstrated by the SlowITe tool.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data= 3.1.1CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify MQTT broker softwareList running processes or services on the system that handle MQTT connections (common brokers include Mosquitto, HiveMQ, EMQ X, ActiveMQ). Check listening ports for 1883 (MQTT) or 8883 (MQTT/TLS).Affected if An MQTT broker is running that implements the MQTT 3.1.1 protocol without enforcing maximum Keep-Alive limits on incoming connections.
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Review broker configuration for Keep-Alive limitsExamine the MQTT broker configuration files or running parameters for settings that restrict maximum client-suggested Keep-Alive values (commonly named max_keep_alive, max_keepalive, connection_timeout, or similar).Affected if No maximum Keep-Alive setting is configured, or the configured maximum exceeds 60-300 seconds, allowing clients to specify arbitrarily large values.
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Test broker Keep-Alive acceptanceConnect to the broker using an MQTT client tool and set an unusually high Keep-Alive value (e.g., 3600 seconds or higher) in the CONNECT packet. Observe whether the broker accepts the connection without enforcing an internal limit.Affected if The broker accepts the connection with a large Keep-Alive value and maintains the connection for the full 1.5x Keep-Alive duration without disconnecting earlier.
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Check connection limits and rate limitingInspect broker or network-level settings for connection rate limits, concurrent connection limits, or connection pool restrictions.Affected if No connection rate limiting or maximum concurrent connection limits are configured, allowing an attacker to exploit Keep-Alive exhaustion.
A system is affected if it runs an MQTT 3.1.1 broker that accepts client-specified Keep-Alive values without enforcing a reasonable maximum limit and lacks connection rate limiting.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
From vendor dataImplement server-side enforcement of maximum Keep-Alive values (e.g., capping at 60-300 seconds) and/or deploy connection rate limiting and connection pool limits at the broker or network level to mitigate resource exhaustion from slow-rate connection attacks.
- Consultation2.0 h
- Implementation4.0 h
- Testing3.0 h
- Review / QA2.0 h
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Free · runs locallyCheck whether your project pulls in CVE-2020-13849 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2020-13849 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Verified mitigations, workarounds, and config changes
- Version or environment caveats, and links to real fixes
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