Resource exhaustion in Messagepack
CVE-2026-48514
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, UnsafeBlitFormatterBase<T>.Deserialize reads an attacker-controlled byteLength from an extension payload and allocates an array based on that value before validating it against the extension header length or remaining payload bytes. The outer extension header is bounded by available input, but that bound is not used to constrain the inner byteLength before allocation. A very small payload can therefore request a very large T[] allocation. 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-w567-… (Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-48514?
- CVE-2026-48514 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-2026-48514?
- High severity. CVSS v3 base score is 7.5 out of 10.