msgpack5: Quadratic parsing in the streaming decoder
Impact
The streaming decoder reparses an incomplete container from the beginning whenever another chunk arrives. A remote peer can split one valid MessagePack value across many small chunks, causing quadratic CPU usage and blocking the event loop.
Patches
The decoder now preserves incremental container state so completed elements are not parsed again when more input arrives.
Workarounds
Buffer each complete MessagePack value before decoding it, or limit the number of chunks accepted for a single value.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| npm package | msgpack5 | < 6.1.0 | 6.1.0 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-407- Platform
- npm
- Package
msgpack5- Disclosed
- 08.10.2026
- Updated
- 11.10.2026 10:22
Sources and licenses
OSV / GitHub Advisory Database - GHSA-gcx5-hxj7-gpqq - CC BY 4.0
Vulnerability history: msgpack5
All published vulnerabilities of this package (npm package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 8
- First → latest
- 03.2021 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- High 2
- Medium 5
- Low 1
Disclosures per year
- 2021: 1
- 2022: 0
- 2023: 0
- 2024: 0
- 2025: 0
- 2026: 7
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msgpack5: Quadratic parsing in the streaming decoder this entry
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