CVE-2019-9749: An issue was discovered in the MQTT input plugin in Fluent Bit through 1.0.4. When this plugin acts as an MQTT broker (server), it mishandles incoming...

Description

An issue was discovered in the MQTT input plugin in Fluent Bit through 1.0.4. When this plugin acts as an MQTT broker (server), it mishandles incoming network messages. After processing a crafted packet, the plugin's mqtt_packet_drop function (in /plugins/in_mqtt/mqtt_prot.c) executes the memmove() function with a negative size parameter. That leads to a crash of the whole Fluent Bit server via a SIGSEGV signal.

Metrics

CVSS 3.1

7.5/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS Probability

1.66%

73.6th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-681

Affected Software

Vendor	Product	Versions
Treasuredata	Fluent Bit	<= 1.0.4

References

https://github.com/fluent/fluent-bit/issues/1135Exploit, Third Party Advisory
https://github.com/fluent/fluent-bit/issues/1135Exploit, Third Party Advisory

Timeline

Published: Mar 13, 2019
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2019-9749?

An issue was discovered in the MQTT input plugin in Fluent Bit through 1.0.4. When this plugin acts as an MQTT broker (server), it mishandles incoming network messages. After processing a crafted packet, the plugin's mqtt_packet_drop function (in /plugins/in_mqtt/mqtt_prot.c) executes the memmove() function with a negative size parameter. That leads to a crash of the whole Fluent Bit server via a SIGSEGV signal.

How severe is CVE-2019-9749?

CVE-2019-9749 has a CVSS score of 7.5/10 (HIGH severity). The EPSS model estimates a 1.66% probability of exploitation in the next 30 days.

How do I fix CVE-2019-9749?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

How Strix Helps

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