CVE-2026-57585: MessagePack is the serializer implementation for Python msgpack.org

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HIGH 7.5REMOTEUPGRADE

CVE-2026-57585 is a high-severity flaw (CVSS 7.5) affecting messagepack. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	7.5 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.5% (top 58%)
CISA exploited list	No
Weakness	CWE-416
Published	2026-06-30
Last modified	2026-10-25

Publisher (CNA): GitHub, Inc. · Vendor: msgpack

Last updated 2026-10-25 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-06-30 22:16 UTCPublished CVE record published
2026-10-25 21:10 UTCUpdated Record last modified

msgpack messagepack UPGRADE

Affected: < 1.2.1

Fixed in: 1.2.1

Safe to downgrade to: no unaffected older release

1. Check installed version

pip show messagepack

2. UPGRADE to 1.2.1

pip install --upgrade "messagepack>=1.2.1"

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-57585?

messagepack: upgrade to 1.2.1. Exact commands for each OS are on this page.

Is CVE-2026-57585 being exploited?

CVE-2026-57585 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-57585 affect?

CVE-2026-57585 affects messagepack. Severity is high (CVSS 7.5). 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

How urgent is CVE-2026-57585?

Priority 42/100. High severity; Remotely exploitable, no login, no user action

Software pages

Python vulnerabilities

Related CVEs

CVE-2026-54522 MEDIUM 5.4 UPGRADE MessagePack for Ruby is an implementation of the MessagePack binary serialization format

References

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