CVE-2021-36088Network attack vector

Service crash via JSON parser double free

Published Jul 1, 2021 · Updated Aug 4, 2024

Double free in Fluent Bit 1.7.0 through 1.7.4 allows remote attackers to crash the service through crafted JSON input. flb_parser_json_do frees mp_buf when it differs from tmp_out_buf but leaves the freed pointer non-null, allowing later cleanup to free it again. Exploitation requires untrusted JSON to reach a configured JSON parser, and a successful trigger interrupts telemetry processing.

CVSS severity9.8
Critical
EPSS probability2.38%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Double free in Fluent Bit 1.7.0 through 1.7.4 allows remote attackers to crash the service through crafted JSON input. flb_parser_json_do frees mp_buf when it differs from tmp_out_buf but leaves the freed pointer non-null, allowing later cleanup to free it again. Exploitation requires untrusted JSON to reach a configured JSON parser, and a successful trigger interrupts telemetry processing.

The record

CVE
CVE-2021-36088
Published
Jul 1, 2021
Updated
Aug 4, 2024
Vendor
Fluent Bit
Product
Fluent Bit
Classifications
CWE-415, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 1, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=1.7.0 <=1.7.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Fluent Bit · Fluent Bitversion=1.7.0 <=1.7.4

Published CVSS scores

9.8BitnamiCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-415Double Free
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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