What is CVE-2021-46878?

CVE-2021-46878 is a high-severity vulnerability in Treasuredata Fluent Bit, classified under Access of Resource Using Incompatible Type (Type Confusion). CVSS score: 7.8/10. Published 2023-04-11.

How severe is CVE-2021-46878?

High severity. CVSS v3 base score is 7.8 out of 10.

Vulnerability in Treasuredata Fluent Bit

CVE-2021-46878

An issue was discovered in Treasure Data Fluent Bit 1.7.1, erroneous parsing in flb_pack_msgpack_to_json_format leads to type confusion bug that interprets whatever is on the stack as msgpack maps and arrays, leading to use-after-free. This can be used by an attacker to craft a specially craft file and trick the victim opening it using the affect software, triggering use-after-free and execute arbitrary code on the target system.

Published 2023-04-11 · last modified 2026-06-17.

CVSS v3 metric

CVSS v3 base score 7.8 (High). Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H.

EPSS exploit prediction

EPSS: 0.004 (26.1th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 26th percentile — 26.1% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000

Affected products

Treasuredata Fluent Bit — versions 1.7.1

Weakness classification (CWE)

CWE-843 — Access of Resource Using Incompatible Type (Type Confusion)

References

bugs.chromium.org/p/oss-fuzz/issues/detail (Exploit, Patch, Third Party Advisory, Issue Tracking)
github.com/fluent/fluent-bit/pull/3115 (Patch)

Frequently asked questions

What is CVE-2021-46878?: CVE-2021-46878 is a high-severity vulnerability in Treasuredata Fluent Bit, classified under Access of Resource Using Incompatible Type (Type Confusion). CVSS score: 7.8/10. Published 2023-04-11.
How severe is CVE-2021-46878?: High severity. CVSS v3 base score is 7.8 out of 10.