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msgpack-python EUVDEUVD-2026-40423

| CVE-2026-57585 HIGH
Use After Free (CWE-416)
2026-06-30 security-advisories@github.com
Buffer Overflow Python Use After Free Memory Corruption Red Hat Messagepack Msgpack
7.5
CVSS 3.1 · Vendor: github
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Severity by source

Vendor (github) PRIMARY
7.5 HIGH
AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
vuln.today AI
5.9 MEDIUM

Network-reachable and unauthenticated, but exploitation depends on the app reusing an Unpacker after a caught error, so AC:H; impact is crash-only, hence C:N/I:N/A:H.

3.1 AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
4.0 AV:N/AC:H/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N
SUSE
HIGH
qualitative
Red Hat
7.5 HIGH
qualitative

Primary rating from Vendor (github).

CVSS VectorVendor: github

Attack Vector
Network
Attack Complexity
Low
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

Lifecycle Timeline

2
Patch available
Jun 30, 2026 - 23:01 EUVD
Analysis Generated
Jun 30, 2026 - 22:30 vuln.today

Blast Radius

ecosystem impact
† from your stack dependencies † transitive graph · vuln.today resolves 4-path depth
  • 29 pypi packages depend on msgpack (16 direct, 13 indirect)

Ecosystem-wide dependent count for version 1.2.1.

DescriptionCVE.org

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.

Articles & Coverage 1

News 5 New Python Vulnerabilities - 2 Critical, 3 High Severity Jul 01, 2026

AnalysisAI

Denial of service in the msgpack-python serialization library (versions prior to 1.2.1) lets remote attackers crash a process via an out-of-bounds read when an application reuses an Unpacker instance after a previously raised error was caught. Sending malformed MessagePack data that triggers an error, then feeding further data to the same Unpacker, can drive the process to a SEGV. No public exploit has been identified at time of analysis, and EPSS data was not provided, but the CVSS 3.1 score of 7.5 (availability-only) reflects a straightforward, unauthenticated crash condition.

Technical ContextAI

msgpack-python is the CPython binding (largely Cython/C) for the MessagePack binary serialization format, widely used to deserialize compact binary payloads in RPC frameworks, caches, message queues, and ML tooling. The defect lives in the Unpacker streaming-decode object: after an exception is raised and caught mid-stream, internal buffer/offset state is left inconsistent, so a subsequent feed/unpack on the same instance reads past valid buffer bounds. NVD classifies this as CWE-416 (Use After Free) and the GitHub tags add Buffer Overflow / Memory Corruption, though the advisory text describes the concrete manifestation as an out-of-bounds read causing a crash rather than confirmed exploitable memory corruption.

RemediationAI

Upgrade msgpack to the fixed release - Vendor-released patch: 1.2.1 - by pinning msgpack>=1.2.1 in requirements and rebuilding/redeploying, per advisory GHSA-6v7p-g79w-8964 (https://github.com/msgpack/msgpack-python/security/advisories/GHSA-6v7p-g79w-8964). If immediate upgrade is not possible, the targeted workaround is to stop reusing an Unpacker instance after an exception: discard the Unpacker and instantiate a fresh one (or drop/reset the connection) whenever a decode error is caught, which removes the inconsistent-state trigger at the cost of losing any buffered stream continuation. Additionally, validate or size-limit untrusted MessagePack input and isolate decoding in a restartable worker so a SEGV degrades to a recoverable restart rather than a full outage; review the fixing commit 2c56ddb5d0025ed481d962c0f5d62d19dec7476d to confirm coverage of your usage pattern.

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Vendor StatusVendor

SUSE

Severity: Important
Product Status
SUSE Linux Enterprise High Performance Computing 15 SP4-ESPOS Fixed
SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS Fixed
SUSE Linux Enterprise High Performance Computing 15 SP5-ESPOS Fixed
SUSE Linux Enterprise High Performance Computing 15 SP5-LTSS Fixed
SUSE Linux Enterprise High Performance Computing 15 SP7 SUSE Linux Enterprise Module for Public Cloud 15 SP7 SUSE Linux Enterprise Server 15 SP7 SUSE Linux Enterprise Server for SAP Applications 15 SP7 Fixed

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EUVD-2026-40423 vulnerability details – vuln.today
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