EUVD-2026-38381Severity by source
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Network-reachable unauthenticated path but requires specific multi-dimensional array schema (AC:H); pure heap-exhaustion availability impact, no confidentiality or integrity effect.
Primary rating from Vendor (GitHub_M).
CVSS VectorVendor: GitHub_M
CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
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2DescriptionCVE.org
MessagePack for C
is a MessagePack serializer for C#. Prior to 2.5.301 and 3.1.7, MessagePack-CSharp's multi-dimensional array formatters read dimension lengths directly from the payload and allocate T[,], T[,,], or T[,,,] before validating that the dimension product matches the encoded element count. The formatter reads a guarded element array header, but allocation of the target multi-dimensional array happens before the dimensions are checked against that element count. A small payload can therefore declare large dimensions, provide an empty or tiny inner array, and cause a large heap allocation before element data is validated. This vulnerability is fixed in 2.5.301 and 3.1.7.
AnalysisAI
Heap exhaustion via crafted multi-dimensional array payloads in MessagePack-CSharp affects all v2.x releases before 2.5.301 and all v3.x releases before 3.1.7, enabling remote unauthenticated attackers to trigger disproportionately large heap allocations with minimal payload bytes. The multi-dimensional array formatters (T[,], T[,,], T[,,,]) allocate based on attacker-supplied dimension values before cross-validating against the encoded element count, so a payload declaring a 10000×10000 array with only a handful of elements forces a massive allocation before any guard fires. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | The vulnerable application must be deserializing MessagePack payloads received from an untrusted source, AND the deserialized object graph must include at least one field or property typed as a multi-dimensional array (T[,], T[,,], or T[,,,]). … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 vector (AV:N/AC:H/AT:P/PR:N/UI:N/VA:L/SC:N/SI:N/SA:N) signals a network-reachable, unauthenticated path with a Low availability impact, but AC:H and AT:P together indicate meaningful preconditions must be satisfied before exploitation is possible. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker submits a crafted MessagePack-encoded message to a publicly reachable API endpoint that deserializes a type containing a two-dimensional array field. The payload encodes dimension sizes of, for example, 50,000×50,000 integers but provides only a few actual elements, causing the server process to allocate roughly 10 GB of managed heap before the element-count guard fires and the allocation is discarded. … |
| Remediation | Upgrade to MessagePack-CSharp 2.5.301 (v2 branch) or 3.1.7 (v3 branch), both of which correct the allocation-before-validation ordering in the multi-dimensional array formatters; the vendor advisory is at https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-cxmj-83gh-fp49. … Detailed patch versions, workarounds, and compensating controls in full report. |
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