CVE-2026-48509
MessagePack-CSharp: ASP.NET Core MessagePackInputFormatter defaults to TrustedData for HTTP request bodies
Description
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, the parameterless MessagePackInputFormatter() constructor uses default serializer options, which resolve to MessagePackSerializerOptions.Standard with MessagePackSecurity.TrustedData. The formatter is designed for ASP.NET Core MVC request bodies, which commonly cross an HTTP trust boundary. This insecure default can expose applications to denial-of-service attacks that MessagePackSecurity.UntrustedData is intended to mitigate, such as hash-collision attacks against dictionary-like model properties. This vulnerability is fixed in 2.5.301 and 3.1.7.
INFO
Published Date :
June 22, 2026, 10:16 p.m.
Last Modified :
June 25, 2026, 4:16 p.m.
Remotely Exploit :
Yes !
Source :
[email protected]
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS | 134c704f-9b21-4f2e-91b3-4a467353bcc0 | |||||
| CVSS 3.1 | CRITICAL | [email protected] | ||||
| CVSS 4.0 | MEDIUM | [email protected] |
Solution
- Update MessagePack for C# to version 2.5.301.
- Update MessagePack for C# to version 3.1.7.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2026-48509.
| URL | Resource |
|---|---|
| https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-2f33-pr97-265q | Mitigation Vendor Advisory |
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2026-48509 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2026-48509
weaknesses.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2026-48509 vulnerability anywhere in the article.
The following table lists the changes that have been made to the
CVE-2026-48509 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
-
CVE Modified by [email protected]
Jun. 25, 2026
Action Type Old Value New Value Changed Affected [{'vendor': 'MessagePack-CSharp', 'product': 'MessagePack-CSharp', 'versions': [{'status': 'affected', 'version': '>= 3.1.7, < 3.1.7'}, {'status': 'affected', 'version': '< 2.5.301'}]}] [{'vendor': 'MessagePack-CSharp', 'product': 'MessagePack-CSharp', 'versions': [{'status': 'affected', 'version': '>= 3.0, < 3.1.7'}, {'status': 'affected', 'version': '< 2.5.301'}]}] -
Initial Analysis by [email protected]
Jun. 23, 2026
Action Type Old Value New Value Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H Added CPE Configuration OR *cpe:2.3:a:messagepack:messagepack:*:*:*:*:*:c#:*:* versions up to (excluding) 2.5.301 *cpe:2.3:a:messagepack:messagepack:*:*:*:*:*:c#:*:* versions from (including) 3.0.3 up to (excluding) 3.1.7 Added Reference Type GitHub, Inc.: https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-2f33-pr97-265q Types: Mitigation, Vendor Advisory -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Jun. 23, 2026
Action Type Old Value New Value Added SSVC {'id': 'CVE-2026-48509', 'role': 'CISA Coordinator', 'options': [{'exploitation': 'none'}, {'automatable': 'no'}, {'technicalImpact': 'partial'}], 'version': '2.0.3', 'timestamp': '2026-06-23T12:36:18.860613Z'} -
New CVE Received by [email protected]
Jun. 22, 2026
Action Type Old Value New Value Added Affected [{'vendor': 'MessagePack-CSharp', 'product': 'MessagePack-CSharp', 'versions': [{'status': 'affected', 'version': '>= 3.1.7, < 3.1.7'}, {'status': 'affected', 'version': '< 2.5.301'}]}] Added Description MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, the parameterless MessagePackInputFormatter() constructor uses default serializer options, which resolve to MessagePackSerializerOptions.Standard with MessagePackSecurity.TrustedData. The formatter is designed for ASP.NET Core MVC request bodies, which commonly cross an HTTP trust boundary. This insecure default can expose applications to denial-of-service attacks that MessagePackSecurity.UntrustedData is intended to mitigate, such as hash-collision attacks against dictionary-like model properties. This vulnerability is fixed in 2.5.301 and 3.1.7. Added CVSS V4.0 AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X Added CWE CWE-1188 Added Reference https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-2f33-pr97-265q