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Vulnerability record · CVE-2026-48515 · published 22 June 2026

CVE-2026-48515: Messagepack allocation without limits vulnerability

Messagepack · Messagepack

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePack-CSharp's multi-dimensional array formatters read dimension lengths directly from the payload and allocate T[,], T[,,], or T[,,,] before validating that the dimension product matches the encoded element count. The formatter reads a guarded element array header, but allocation of the target multi-dimensional array happens before the dimensions are checked against that element count. A small payload can therefore declare large dimensions, provide an empty or tiny inner array, and cause a large heap allocation before element data is validated. This vulnerability is fixed in 2.5.301 and 3.1.7.

6.3 CVSS 4.0 Medium EPSS 0.40% · top 67.8% CWE-770 · Allocation without limits
6.3CVSS 4.0 base score
0.40%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
1References
25 Jun 2026Last modified by NVD

Description

MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePack-CSharp's multi-dimensional array formatters read dimension lengths directly from the payload and allocate T[,], T[,,], or T[,,,] before validating that the dimension product matches the encoded element count. The formatter reads a guarded element array header, but allocation of the target multi-dimensional array happens before the dimensions are checked against that element count. A small payload can therefore declare large dimensions, provide an empty or tiny inner array, and cause a large heap allocation before element data is validated. This vulnerability is fixed in 2.5.301 and 3.1.7.

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/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:

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-cxmj-83gh-fp49 MitigationVendor Advisory

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Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-48515), CISA KEV, FIRST EPSS (scores of 2026-09-27). This page is refreshed as NVD updates the record.