What’s Vulnerable › Vulnerabilities

CVE-2026-57585: MessagePack: Out-of-bounds read/crash on Unpacker reuse after caught error

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.5% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-06-30 · updated 2026-10-25
• Weakness: CWE-416

Description

MessagePack is the serializer implementation for Python msgpack.org. Prior to 1.2.1, there is an Out-of-bounds read/crash on Unpacker reuse after a caught error, potentially leading to a DoS attack. If the Unpacker is used repeatedly after an error occurs, the process may crash with a SEGV. This issue has been fixed in version 1.2.1.

Affected products

• msgpack Messagepack: before 1.2.1 — fixed in 1.2.1
• Pypi Msgpack: before 1.2.1; 0.5.0, 0.5.1, 0.5.2, 0.5.3, 0.5.4, 0.5.5 (+26) — fixed in 1.2.1

How to fix

Upgrade to a fixed version: msgpack Messagepack 1.2.1; Pypi Msgpack 1.2.1. Check the vendor advisory for mitigations.

References

• https://github.com/msgpack/msgpack-python/commit/2c56ddb5d0025ed481d962c0f5d62d19dec7476d
• https://github.com/msgpack/msgpack-python/security/advisories/GHSA-6v7p-g79w-8964

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