How severe is CVE-2026-57585?

CVE-2026-57585 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2026-57585?

CVE-2026-57585 affects the following packages: msgpack (PyPI). Ecosystems affected: PyPI.

How do I fix CVE-2026-57585?

Update msgpack to 1.2.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-57585 is resolved across your whole dependency graph.

How do I detect CVE-2026-57585 in my PyPI dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for msgpack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-57585 if there is no patch (or I can't update yet)?

Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Is CVE-2026-57585 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-57585 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-57585?

CVE-2026-57585 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 40th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-57585?

CVE-2026-57585 is classified as Use After Free (CWE-416). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-57585 published, and has it been updated?

CVE-2026-57585 was published on June 30, 2026 and was last updated on October 5, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐍

🐍 PyPI

Not in CISA KEV

HIGH severity

CVE-2026-57585 — msgpack

HIGHFix: msgpack/msgpack-python@2c56ddb

CVE-2026-57585 is a high-severity (CVSS 7.5) Use After Free vulnerability in msgpack. A fix is available for msgpack — see the affected versions and patch details below.

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

Also known asGHSA-6v7p-g79w-8964PYSEC-2026-3625

Published

Jun 30, 2026

Updated

Oct 5, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-57585.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk+0.21%

Lower risk than most CVEs40th percentile — riskier than 40% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

CVE-2026-57585 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected

🐍msgpack

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects PyPI packages — download data is not available via public APIs for these ecosystems.

Description

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 Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐍PyPI	`msgpack`	all versions	1.2.1`pip install --upgrade 'msgpack==1.2.1'`

Affected Products

1 product · 1 configurations

Application

messagepackmsgpack

< 1.2.1

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for msgpack, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update msgpack to 1.2.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-57585 is resolved across your whole dependency graph.
Workarounds
Constrain what reaches the vulnerable code: limit the size and shape of untrusted input, isolate the affected component in a sandboxed or least-privileged process, and enable the platform's memory-safety mitigations (ASLR, stack protector, hardened allocator) so an out-of-bounds access is more likely to fail closed than to be exploitable.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

This Important flaw in MessagePack for Python can lead to a denial of service. An out-of-bounds read and subsequent process crash may occur if an Unpacker instance is reused after an error has been caught, potentially allowing an attacker to disrupt services that process MessagePack data.

Workaround published by Red Hat

To mitigate this issue, applications utilizing MessagePack for Python should be reviewed to ensure that `Unpacker` instances are not reused after an error has occurred during unpacking. Instead, a new `Unpacker` instance should be created for subsequent operations.

Source: Red Hat security advisory for CVE-2026-57585 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat AI Inference Server 3.2	`rhaiis/vllm-cuda-rhel9:1790621718`	RHSA-2026:73929
Red Hat AI Inference Server 3.2	`rhaiis/vllm-rocm-rhel9:1790621713`	RHSA-2026:73930
Red Hat AI Inference Server 3.4	`rhaii/vllm-cpu-rhel9:1790075793`	RHSA-2026:70965
Red Hat AI Inference Server 3.4	`rhaii/vllm-cuda-rhel9:1790090131`	RHSA-2026:70979
Red Hat AI Inference Server 3.4	`rhaii/vllm-rocm-rhel9:1790109620`	RHSA-2026:70995

Frequently Asked Questions

### 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 disca