Type-policy bypass via wrapped typeless payloads
Published Jun 22, 2026 · Updated Jun 22, 2026
Unsafe typeless deserialization in MessagePack for C# before 2.5.301 and 3.0 through 3.1.6 allows remote attackers to bypass type blocks. ThrowIfDeserializingTypeIsDisallowed checks only the outer type name, so arrays and generic containers can hide a blocked inner type while formatter creation still materializes it. Exploitation requires an application to deserialize attacker-supplied typeless ext-100 data; the resulting integrity impact depends on the reachable blocked or gadget type.
Summary
What happened
Unsafe typeless deserialization in MessagePack for C# before 2.5.301 and 3.0 through 3.1.6 allows remote attackers to bypass type blocks. ThrowIfDeserializingTypeIsDisallowed checks only the outer type name, so arrays and generic containers can hide a blocked inner type while formatter creation still materializes it. Exploitation requires an application to deserialize attacker-supplied typeless ext-100 data; the resulting integrity impact depends on the reachable blocked or gadget type.
The record
- CVE
- CVE-2026-48517
- Published
- Jun 22, 2026
- Updated
- Jun 22, 2026
- Vendor
- MessagePack-CSharp
- Product
- MessagePack for C#
- Classifications
- CWE-470, CWE-502
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Jun 22, 2026CVE publishedPublication date reported by the CVE source.
- Jun 22, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 2.5.301
- Affected versionversion=>= 3.1.7, < 3.1.7
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
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Technologies
Your stack
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Your stack
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