What is CVE-2026-57585?

CVE-2026-57585 is a high-severity vulnerability in Msgpack Messagepack, classified under Use After Free. CVSS score: 7.5/10. Published 2026-06-30.

How severe is CVE-2026-57585?

High severity. CVSS v3 base score is 7.5 out of 10.

Use After Free in Msgpack Messagepack

CVE-2026-57585

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.

Vulnerability class: Use-After-Free

Published 2026-06-30 · last modified 2026-08-06.

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.005 (39.6th percentile), scored 2026-09-30.

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 40th percentile — 39.6% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS over last 30 days · oldest: 0.005 · newest: 0.005 · change: 0.000

Affected products

Msgpack Messagepack
Msgpack Msgpack-Python — versions < 1.2.1

Weakness classification (CWE)

CWE-416 — Use After Free

References

github.com/msgpack/msgpack-python/security/advisories/GHSA-6v7p-g79w-8964 (Mitigation, Vendor Advisory)
github.com/msgpack/msgpack-python/commit/2c56ddb5d0025ed481d962c0f5d62d19dec747… (Patch)

Frequently asked questions

What is CVE-2026-57585?: CVE-2026-57585 is a high-severity vulnerability in Msgpack Messagepack, classified under Use After Free. CVSS score: 7.5/10. Published 2026-06-30.
How severe is CVE-2026-57585?: High severity. CVSS v3 base score is 7.5 out of 10.