MessagePack for Python: Out-of-bounds read / crash on Unpacker reuse after a caught error
Impact
If the Unpacker is used repeatedly after an error occurs, the process may crash with a SEGV.
If the Unpacker is used repeatedly to unpack untrusted input from external sources, it may be vulnerable to a DoS attack.
Patches
v1.2.1
Workarounds
Users should create a new Unpacker instead of reusing the same Unpacker after an error occurs.
Applying the above patch can prevent SEGV, but reusing the Streaming Unpacker after it has encountered an error will not yield correct data. If an error occurs during Streaming Unpacking, the Stream and Streaming Unpacker should be discarded.
Therefore, this is not just a workaround but the correct solution. The above patch only prevents crashes from incorrect usage.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | msgpack | < 1.2.1 | 1.2.1 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-416- Platform
- Python (PyPI)
- Package
msgpack- Disclosed
- 19.06.2026
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2026-3625 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-6v7p-g79w-8964 - CC BY 4.0
Vulnerability history: msgpack
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
This is the only known vulnerability of this package.
Know which vulnerabilities affect your application
With the DockRay integration and software inventory enabled, DockRay checks reported component versions against known vulnerabilities and notifies you about confirmed matches. Coverage depends on the supported technology and available advisory data.