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CVE-2026-48509

33
FAUCET Score

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.

First published: Jun 22, 2026Last modified: Jun 25, 2026

Impacted Technologies

VendorProductVersion(s)CPE
< 2.5.301CPE matchmatch criteria
cpe:2.3:a:messagepack:messagepack:*:*:*:*:*:c\#:*:*
>= 3.0.3, < 3.1.7CPE matchmatch criteria
cpe:2.3:a:messagepack:messagepack:*:*:*:*:*:c\#:*:*

CVSS Data

CVSS version used by this source: 4.0

6.3MEDIUM

CVSS:4.0/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

Attack Vector
NETWORK
Attack Complexity
HIGH
Attack Requirements
PRESENT
Privileges Required
NONE
User Interaction
NONE
VS Confidentiality
NONE
VS Integrity
LOW
VS Availability
LOW
SS Confidentiality
NONE
SS Integrity
NONE
SS Availability
NONE
Exploit Maturity
NOT_DEFINED
CvssVersion
4.0

Exploit Intelligence

EPSS Score
0.25%
Probability of exploitation in next 30 days
EPSS Percentile
16.4%
Percentile rank of EPSS score among Peer Group
As of 2026-07-27
Model: v2026.06.15
This CVE's current EPSS score of 0.0025 is in the 1st percentile among its peer group of 36,897 CVEs.

Social Chatter

The average CVE in this peer group has 0.0 Twitter, 0.1 Reddit, 0.3 Bluesky, 0.3 Mastodon, and 2.4 GitHub mentions.

Media Mentions

No media coverage found for this CVE.

The average CVE in this peer group has 0.3 InfoSec Media, 0.0 Vendor Blog, and 0.0 Security Researcher mentions.

Remediation

Patch Available

Vendor Patches (3)

nugetpatch availablevia ghsa
Product: MessagePackFixed in: 2.5.301
nugetpatch availablevia ghsa
Product: MessagePackFixed in: 3.1.7
github_advisoryworkaround availablevia nvd_reference
View patch

Vendor Advisories (1)

nugetGHSA-2f33-pr97-265qmedium

MessagePack-CSharp: ASP.NET Core MessagePackInputFormatter defaults to TrustedData for HTTP request bodies

Jun 25, 2026

References

github.com / MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-2f33-pr97-265q
MitigationVendor Advisory