RCE in Messagepack
CVE-2026-48502
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePackReader.ReadDateTime() can allocate stack memory based on an attacker-controlled MessagePack extension length. In the slow path for timestamp extension parsing, the computed tokenSize includes the extension body length from the wire and is used in a stackalloc operation before the extension length is validated as one of the valid timestamp sizes. A very small payload can claim a large timestamp extension body and cause a stack allocation large enough to trigger an uncatchable StackOverflowException, terminating the host process. This vulnerability is fixed in 2.5.301 and 3.1.7.
Vulnerability class: Buffer Overflow
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 (35.6th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 36th percentile — 35.6% 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, < 2.5.301
Weakness classification (CWE)
- CWE-125 — Out-of-bounds Read
- CWE-190 — Integer Overflow or Wraparound
- CWE-407 — Inefficient Algorithmic Complexity
- CWE-409 — Improper Handling of Highly Compressed Data (Data Amplification)
- CWE-470 — Use of Externally-Controlled Input to Select Classes or Code (Unsafe Reflection)
- CWE-502 — Deserialization of Untrusted Data
- CWE-674 — Uncontrolled Recursion
- CWE-789
- CWE-1188 — Initialization of a Resource with an Insecure Default
References
- github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-382j-… (Mitigation, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-48502?
- CVE-2026-48502 is a high-severity vulnerability in Messagepack, classified under Out-of-bounds Read. CVSS score: 7.5/10. Published 2026-06-22.
- How severe is CVE-2026-48502?
- High severity. CVSS v3 base score is 7.5 out of 10.