CVE-2026-57585

highCVSS 7.5covered by 2 sourcesfirst seen 2026-06-09

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.

CSIRTS triage

What: An out-of-bounds read/crash occurs on Unpacker reuse after an error is caught.
Who is affected: Deployments using MessagePack for data unpacking are affected.
Urgency: Remediation is urgent due to high severity and potential for exploitation.
Action: Update to the latest version of MessagePack to mitigate this vulnerability.

AI-assisted analysis generated from the source advisory — verify against the original.

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Exploitation outlook

Low exploitation risk0.28% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 20% of all EPSS-scored CVEs.

Advisory coverage (2)

highCVE-2026-57585: MessagePack is the serializer implementation for Python msgpack.org. Prior to 1.2.1, there is …nvd · 2026-06-30
highCVE-2026-57585: MessagePack: Out-of-bounds read/crash on Unpacker reuse after caught errormsrc · 2026-06-09

External references

NVD record for CVE-2026-57585

CVE.org record

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