CVE-2020-13849: The MQTT protocol 3.1.1 requires a server to set a timeout value of 1.5 times the Keep-Alive value specified b

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HIGH 7.5REMOTEDOWNGRADE

CVE-2020-13849 is a high-severity flaw (CVSS 7.5) affecting mqtt. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The 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.

Why this priority

High severity
Remotely exploitable, no login, no user action

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	2.1% (top 19%)
CISA exploited list	No
Weakness	CWE-400
Published	2020-06-04
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: mqtt

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2020-06-04 21:15 UTCPublished CVE record published
2026-06-17 02:53 UTCUpdated Record last modified

mqtt mqtt DOWNGRADE

Affected: 3.1.1

Fixed in: no fixed release known

Safe to downgrade to: a release before 3.1.1

1. Check installed version

apt-cache policy mqtt || rpm -q mqtt || mqtt --version

2. No fixed release: DOWNGRADE to a release before 3.1.1 (Debian / Ubuntu)

apt-cache madison mqtt sudo apt install mqtt=<VERSION_BEFORE_3.1.1> sudo apt-mark hold mqtt

2. No fixed release: DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list mqtt sudo dnf downgrade mqtt-<VERSION_BEFORE_3.1.1> sudo dnf versionlock add mqtt

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2020-13849?

mqtt: downgrade or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2020-13849 being exploited?

CVE-2020-13849 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2020-13849 affect?

CVE-2020-13849 affects mqtt. Severity is high (CVSS 7.5). The 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 demo

How urgent is CVE-2020-13849?

Priority 52/100. High severity; Remotely exploitable, no login, no user action

References

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