Vulnerability-Lookup

GHSA-92VJ-HP7M-GWCJ

Vulnerability from github – Published: 2026-05-29 20:02 – Updated: 2026-05-29 20:02

Summary

Nerdbank.MessagePack has Inefficient CPU Computation

Details

Impact

Applications that call OptionalConverters.WithExpandoObjectConverter and deserialize untrusted data are open to a vulnerability by which an attacker can exploit a O(n²) algorithm to burn an inordinate amount of CPU effort by adding a great many properties to an ExpandoObject, whose Add method is implemented as an O(n) algorithm.

Patches

Update to a patched version.

If a project's ExpandoObject data requires more than 128 properties, the default limit should be changed:

this.Serializer = this.Serializer with
{
    StartingContext = this.Serializer.StartingContext with
    {
        Security = this.Serializer.StartingContext.Security with
        {
            ExpandoObjectMaxPropertyCount = 256, // Set this to whatever limit is required by your application
        },
    },
};

Workarounds

Avoid the non-default WithExpandoObjectConverter extension method when deserializing untrusted data. If deserializing untrusted data into an ExpandoObject is required, developers should write a custom converter for their project that limits the number of properties allowed before initializing the object.

Severity

5.3 (Medium)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

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{
  "affected": [
    {
      "package": {
        "ecosystem": "NuGet",
        "name": "Nerdbank.MessagePack"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.2.4"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [],
  "database_specific": {
    "cwe_ids": [
      "CWE-1176"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-05-29T20:02:59Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Impact\n\nApplications that call `OptionalConverters.WithExpandoObjectConverter` and deserialize untrusted data are open to a vulnerability by which an attacker can exploit a `O(n\u00b2)` algorithm to burn an inordinate amount of CPU effort by adding a great many properties to an `ExpandoObject`, whose `Add` method is implemented as an `O(n)` algorithm.\n\n### Patches\n\nUpdate to a patched version.\n\nIf a project\u0027s `ExpandoObject` data requires more than 128 properties, the default limit should be changed:\n\n```cs\nthis.Serializer = this.Serializer with\n{\n\tStartingContext = this.Serializer.StartingContext with\n\t{\n\t\tSecurity = this.Serializer.StartingContext.Security with\n\t\t{\n\t\t\tExpandoObjectMaxPropertyCount = 256, // Set this to whatever limit is required by your application\n\t\t},\n\t},\n};\n```\n\n### Workarounds\n\nAvoid the non-default `WithExpandoObjectConverter` extension method when deserializing untrusted data.\nIf deserializing untrusted data into an `ExpandoObject` is required, developers should write a custom converter for their project that limits the number of properties allowed before initializing the object.",
  "id": "GHSA-92vj-hp7m-gwcj",
  "modified": "2026-05-29T20:02:59Z",
  "published": "2026-05-29T20:02:59Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/AArnott/Nerdbank.MessagePack/security/advisories/GHSA-92vj-hp7m-gwcj"
    },
    {
      "type": "WEB",
      "url": "https://github.com/AArnott/Nerdbank.MessagePack/commit/c5a239e4f20c38548de44c4dd2a782efd5e2547c"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/AArnott/Nerdbank.MessagePack"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Nerdbank.MessagePack has Inefficient CPU Computation"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
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