CVE-2026-92707
MessagePack: Nested arrays can blow past buffer length limits
Published Oct 15, 2026 · corrected/updated Oct 15, 2026 · evidence confidence high
### Impact MessagePack-CSharp is vulnerable to denial of service through excessive memory allocation when deserializing attacker-controlled data into . When encounters an array, it allocates an using the declared array length **before** enforcing the configured maximum object-graph depth. A specially crafted payload containing deeply nested arrays can therefore keep many large arrays live simultaneously before deserialization is rejected for exceeding the depth limit. Because the array-header validation uses the total unread byte count as evidence that the declared elements may be present, nested array headers can reuse the same trailing bytes for this validation. This permits a relatively small payload to cause disproportionately large managed-heap allocations. The reported example uses an approximately 31.5 KiB payload to allocate roughly 114.7 MiB of reference storage on x64—an amplification factor of approximately 3,800—before the depth exception is raised. Repeated requests may cause severe memory pressure, excessive garbage collection, process termination, or loss of service availability. Applications are affected when they: - Deserialize untrusted MessagePack data as , or otherwise use a resolver path that selects ; and - Permit an attacker to submit such data repeatedly. ASP.NET Core SignalR is one known way to expose the vulnerability remotely: an application that enables and has a reachable hub method with an parameter may pass attacker-controlled arguments to the vulnerable MessagePack-CSharp formatter. However, the underlying vulnerability is in MessagePack-CSharp, not SignalR, and other applications that deserialize untrusted data through the same formatter may also be affected. MessagePack-CSharp 2.5.302 is confirmed to contain the vulnerable code. Other releases containing the same allocate-before-depth-check behavior may also be affected. Authentication requirements depend on the application exposing the deserialization endpoint: exploitation require
Grounded briefings
Catalog interpretations for three audiences. Each brief cites ingested metadata and the original advisories below. They are not independent research and they do not invent exploit steps.
Executive
CVE-2026-92707 is a medium public vulnerability record for this product. It is not currently listed in the CISA Known Exploited catalog. Check the linked vendor or CERT advisories for patch status. This summary is a catalog interpretation of the ingested metadata and cites the original advisories below.
System administrator
Identify whether this product is in your estate, then compare installed versions with the affected ranges. Affected packages or ranges on record: MessagePack (0 → 2.5.303); MessagePack (3.0.0 → 3.1.9); MessagePack (< 2.5.303); MessagePack (>= 3.0.0, < 3.1.9). Check the linked vendor or CERT advisories for patch status. Prefer the vendor or distribution advisory linked in Sources before changing production systems. This is a catalog interpretation, not a runbook.
Security analyst
Signals on file: CVSS 5.3. It is not currently listed in the CISA Known Exploited catalog. Weakness classes: CWE-1325. Sources contributing to this record: cve_org, github, gitlab, nvd. Public exploit references, when present, are outbound links only and are not proof of active exploitation. This is a catalog interpretation of stored metadata.
Exploitation and remediation
Exploitation evidence
Not listed as known exploited in CISA KEV. Not in CISA KEV or VulnCheck KEV.
Patch and remediation
No required-action text is stored yet. Use the vendor or CERT links in Sources for patch availability.
Safe detection guidance
Compare installed versions with the affected ranges below and verify the advisory from the original publisher. This site stores metadata and outbound links only; it does not ship exploit code or proof-of-concept payloads.
Code
The project this record applies to. Exploit listings stay in References.
Timeline
Detection, updates, and resolution for this record.
Oct 15, 2026 · GitHub Advisory Database
Detected
### Impact MessagePack-CSharp is vulnerable to denial of service through excessive memory allocation when deserializing attacker-controlled data into . When encounters an array, it allocates an using the declared array length **before** enforcing the configured maximum object-graph depth. A specially crafted payload containing deeply nested arrays can therefore keep many large arrays live simultan
Oct 15, 2026 · GitHub Advisory Database
Updated
### Impact MessagePack-CSharp is vulnerable to denial of service through excessive memory allocation when deserializing attacker-controlled data into . When encounters an array, it allocates an using the declared array length **before** enforcing the configured maximum object-graph depth. A specially crafted payload containing deeply nested arrays can therefore keep many large arrays live simultan
Oct 15, 2026 · GitHub Advisory Database
Fix available
MessagePack fixed in 2.5.303; MessagePack fixed in 3.1.9
Oct 15, 2026 · GitHub Advisory Database
Fix available
MessagePack fixed in 2.5.303
Oct 15, 2026 · GitHub Advisory Database
Fix available
MessagePack fixed in 3.1.9
Oct 15, 2026 · NIST NVD
Updated
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.303 and 3.1.9, deserializing attacker-controlled MessagePack data as System.Object through PrimitiveObjectFormatter can cause excessive memory allocation. The formatter allocates an object[] from each declared array length before the configured object-graph depth limit rejects the input, while nested array headers can reuse the sa
Affected
- NuGet MessagePack0 → 2.5.303
- NuGet MessagePack3.0.0 → 3.1.9
- nuget MessagePack< 2.5.303
- nuget MessagePack>= 3.0.0, < 3.1.9
- nuget messagepackversion unspecified
Sources
- CVE.orgVulnerability recordCVE-2026-92707
Official CVE identifier
cve.org - GitHub Advisory DatabasePackage advisoryGHSA-qhrr-8q5h-9q3h
GitHub Advisory Database record mirrored by OSV.
github.com - GitLab Advisory DatabasePackage advisoryCVE-2026-92707
MessagePack-CSharp is vulnerable to denial of service through excessive memory allocation when deserializing attacker-controlled data into System.Object. When PrimitiveObjectFormatter encounters an array, it allocates an object[] using the declared array length before enforcing the configured maximum object-graph depth. A specially crafted payload containing deeply nested arrays can therefore keep
advisories.gitlab.com - NIST NVDVulnerability recordCVE-2026-92707
MessagePack for C# is a MessagePack serializer for C#. Prior to 2.5.303 and 3.1.9, deserializing attacker-controlled MessagePack data as System.Object through PrimitiveObjectFormatter can cause excessive memory allocation. The formatter allocates an object[] from each declared ar
nvd.nist.gov - OpenSSF OSV / OSV ScannerPackage advisoryGHSA-qhrr-8q5h-9q3h
MessagePack: Nested arrays can blow past buffer length limits
osv.dev