No. Junglewise Threat Intelligence has no report of CVE-2020-5234 being exploited in the wild.
How severe is CVE-2020-5234?
Low severity, with a CVSS score of 3.1, published 31 January 2020.
Which products and versions are affected?
MessagePack (NuGet) ECOSYSTEM:introduced=0,fixed=1.9.11; MessagePack.ImmutableCollection (NuGet) ECOSYSTEM:introduced=0,fixed=1.9.11; MessagePack.ReactiveProperty (NuGet) ECOSYSTEM:introduced=0,fixed=1.9.11; MessagePack.Unity (NuGet) ECOSYSTEM:introduced=0,fixed=1.9.11; and 1 more.
Is there a fix for CVE-2020-5234?
Yes. MessagePack (NuGet): upgrade to 1.9.11 or later; MessagePack.ImmutableCollection (NuGet): upgrade to 1.9.11 or later; MessagePack.ReactiveProperty (NuGet): upgrade to 1.9.11 or later; MessagePack.Unity (NuGet): upgrade to 1.9.11 or later; MessagePack.UnityShims (NuGet): upgrade to 1.9.11 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.
Am I affected by CVE-2020-5234?
Check whether you run MessagePack (NuGet), MessagePack.ImmutableCollection (NuGet), MessagePack.ReactiveProperty (NuGet) or one of the others listed at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
How to fix
MessagePack (NuGet): upgrade to 1.9.11 or later
dotnet add package MessagePack --version 1.9.11
MessagePack.ImmutableCollection (NuGet): upgrade to 1.9.11 or later