MessagePack-CSharp: Denial of service vulnerabilities can swamp the CPU or crash the process with stack and heap overflows

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.2 · CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-48502: 0.44% estimated exploitation activity in the next 30 days; percentile 38.07 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

Summary 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. Impact Applications are affected when they deserialize untrusted payloads into types containing DateTime values. This path is available through the standard formatter set and does not require opting into typeless serialization, LZ4 compression, Unity-specific resolvers, or other specialized features. MessagePackSecurity.UntrustedData and MaximumObjectGraphDepth do not mitigate this issue because the crash is caused by a single-frame stack…

Published by the source

25 Jun 2026, 18:35 UTC

Last modified by the source

25 Jun 2026, 18:35 UTC

Source last checked

26 Oct 2026, 17:04 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-382j-8mxh-c7x2

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# Patch Next advisory brief: CVE-2026-48502

Advisory: MessagePack-CSharp: Denial of service vulnerabilities can swamp the CPU or crash the process with stack and heap overflows
IDs: CVE-2026-48502, GHSA-382j-8mxh-c7x2
Record: https://patchnext.com/advisories/cve-2026-48502 (revision 1, source checked 26 Oct 2026, 17:04 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: messagepack 3.1.7. A vendor fix does not mean a deployment is fixed.

## Affected components
- NuGet messagepack: affected >= 3.0, < 3.1.7; fixed in 3.1.7

## Suggested inspection (read-only)
- NuGet messagepack: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on messagepack.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-382j-8mxh-c7x2 (GitHub-reviewed advisory GHSA-382j-8mxh-c7x2 lists affected ranges: NuGet messagepack >=3.0 <3.1.7)

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