CVE-2026-48511Network attack vector

Service exhaustion via quadratic ExpandoObject insertion

Published Jun 22, 2026 · Updated Jun 22, 2026

Algorithmic complexity in MessagePack for C# before 2.5.301 and 3.0 through 3.1.6 allows remote attackers to exhaust CPU and memory. ExpandoObjectFormatter.Deserialize calls IDictionary<string, object>.Add for every untrusted map entry, forcing repeated linear name scans and array copies as distinct keys accumulate. Applications are exposed only when attacker-controlled maps are deserialized into ExpandoObject through ExpandoObjectResolver; concurrent payloads can leave a server unresponsive or exhaust process memory.

CVSS severity6.3
Medium
EPSS probability0.40%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Algorithmic complexity in MessagePack for C# before 2.5.301 and 3.0 through 3.1.6 allows remote attackers to exhaust CPU and memory. ExpandoObjectFormatter.Deserialize calls IDictionary<string, object>.Add for every untrusted map entry, forcing repeated linear name scans and array copies as distinct keys accumulate. Applications are exposed only when attacker-controlled maps are deserialized into ExpandoObject through ExpandoObjectResolver; concurrent payloads can leave a server unresponsive or exhaust process memory.

The record

CVE
CVE-2026-48511
Published
Jun 22, 2026
Updated
Jun 22, 2026
Vendor
MessagePack-CSharp
Product
MessagePack for C#
Classifications
CWE-407, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 22, 2026CVE publishedPublication date reported by the CVE source.
  2. 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.

  1. Affected versionversion=< 2.5.301
  2. Affected versionversion=>= 3.1.7, < 3.1.7

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

MessagePack-CSharp · MessagePack for C#version=< 2.5.301; version=>= 3.1.7, < 3.1.7

Published CVSS scores

6.3GitHub, Inc.CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N
7.5NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-407Inefficient Algorithmic Complexity
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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