CVE-2026-48502 MessagePack-CSharp: Denial of service vulnerabilities can swamp the CPU or crash the process with stack and heap overflows
Attackers can crash the host process via stack overflow in MessagePack-CSharp by sending crafted timestamp extension data.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-48502?
CVE-2026-48502 is a high-severity denial of service vulnerability in MessagePack-CSharp, published on 22 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
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.
Weakness: CWE-789, CWE-674, CWE-502, CWE-409, CWE-407, CWE-190, CWE-470, CWE-125, CWE-1188
Which versions are affected by CVE-2026-48502?
2 open source packages ship an affected version, including MessagePack. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
MessagePack NuGet | From 3.0 | 3.1.7 |
MessagePack NuGet | From 3.0 | 3.1.7 |
Products include Messagepack Messagepack.
How do I fix CVE-2026-48502?
Upgrade MessagePack to 3.1.7 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-48502 being exploited?
There is no known exploitation of CVE-2026-48502 in the wild and no public exploit code.
Other vulnerabilities in MessagePack-CSharp
- CVE-2026-48109 MessagePack-CSharp: LZ4 decompression may fail with AccessViolationException after dereferencing memory from bad input
- CVE-2026-48506 MessagePack-CSharp: MessagePackReader.Skip can recurse without enforcing maximum object graph depth
- CVE-2026-48509 MessagePack-CSharp: ASP.NET Core MessagePackInputFormatter defaults to TrustedData for HTTP request bodies
- CVE-2026-48510 MessagePack-CSharp: LZ4 decompression allocates from unbounded declared output lengths
- CVE-2026-48511 MessagePack-CSharp: ExpandoObject formatter can perform quadratic insertion work on untrusted maps
Sources
Also known as GHSA-382j-8mxh-c7x2.