CVE-2021-46878Public exploit

Code execution via unchecked MessagePack object types

Published Apr 11, 2023 · Updated Feb 11, 2025

Type confusion in Treasure Data Fluent Bit 1.7.1 allows attackers to execute arbitrary code when a crafted MessagePack file is opened. The flb_pack_msgpack_to_json_format function accesses array and map union members without confirming that decoded objects have those types, enabling use-after-free. Exploitation requires a victim to open a malicious file, and successful memory corruption runs code in the victim process.

CVSS severity7.8
High
EPSS probability0.35%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Type confusion in Treasure Data Fluent Bit 1.7.1 allows attackers to execute arbitrary code when a crafted MessagePack file is opened. The flb_pack_msgpack_to_json_format function accesses array and map union members without confirming that decoded objects have those types, enabling use-after-free. Exploitation requires a victim to open a malicious file, and successful memory corruption runs code in the victim process.

The record

CVE
CVE-2021-46878
Published
Apr 11, 2023
Updated
Feb 11, 2025
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-843, T1204.002, T1203
Attack vector
local
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 11, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 11, 2025Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectorlocal
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

7.8NVDCVSS:3.1/AV:L/AC:L/PR:N/UI:R/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.

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No observations available

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

Weakness, pattern, technique

CWE-843Access of Resource Using Incompatible Type ('Type Confusion')
T1204.002Malicious File
T1203Exploitation for Client Execution

Public exploit references

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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