Resource exhaustion in Messagepack
CVE-2026-48515
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.
Published · last modified .
CVSS v3 metric
CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.
EPSS exploit prediction
EPSS: 0.004 (32.2th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 32nd percentile — 32.2% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.004 · newest: 0.004 · change: 0.000
Affected products
- Messagepack
- Messagepack-Csharp — versions >= 3.1.7, < 3.1.7, >= 3.0, < 3.1.7, < 2.5.301
Weakness classification (CWE)
References
- github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-cxmj-… (Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-48515?
- CVE-2026-48515 is a high-severity vulnerability in Messagepack, classified under Allocation of Resources Without Limits or Throttling. CVSS score: 7.5/10. Published 2026-06-22.
- How severe is CVE-2026-48515?
- High severity. CVSS v3 base score is 7.5 out of 10.