CVE-2026-92707: MessagePack: Nested arrays can blow past buffer length limits
Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.
Generated by VEDAS. Scores as of 2026-11-01 19:19 UTC. Rebuilt every few hours from cve-scores, CISA KEV and vedas-signatures. How this works and its limits.
What it is
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 same trailing unread bytes to satisfy per-header length validation. A comparatively small payload can therefore keep many large arrays alive at once. When an attacker can submit such data repeatedly, the allocations can cause severe managed-heap pressure, excessive garbage collection, process termination, or loss of service. Exposure requires an application to deserialize untrusted data through the affected formatter path and permit repeated attacker-controlled submissions, such as a reachable ASP.NET Core SignalR hub method with an object parameter and AddMessagePackProtocol() enabled. This issue is fixed in versions 2.5.303 and 3.1.9.
Description quoted from the CVE record (assigned by GitHub_M, published 2026-10-15).
Weakness: CWE-1325: Improperly Controlled Sequential Memory Allocation
How it can be exploited
Exploitable over the network with low attack complexity needing no privileges and no user interaction. Impact: confidentiality none, integrity none, availability low. CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
CISA assessment (SSVC): CISA has no evidence of exploitation. Automatable: yes. Technical impact: partial.
Public exploit evidence (Exploit Observer)
Exploit Observer evidence for this CVE has not been fetched yet.
Live scores
- EPSS
- 0.007
low predicted chance of attack - VEDAS
- 0.813
some exploit evidence - On CISA KEV
- Not listed
- Detection rule
- None yet
Who is affected
| Product | Affected | Not affected |
|---|---|---|
| MessagePack-CSharp MessagePack-CSharp | version < 2.5.303 version >= 3.0.0, < 3.1.9 | Not stated |
Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.
How to fix it
No fixed version or vendor advisory is listed in the CVE record yet. Watch the vendor’s security page.
How to detect it
There is no open VEDAS detection rule for this bug yet. It is listed on the detection gaps page if CISA has confirmed attacks.
Advisories on this CVE
- Microsoft October 2026 Patch Tuesday: exploited Windows Shell MOTW bypass (CVE-2026-96951) and two disclosed .NET flaws (full advisory)
- Microsoft October Patch Tuesday: exploited Windows Shell bypass and a disclosed .NET Framework WDAC bypass (CVE-2026-96951, CVE-2026-108398, CVE-2026-92707) (13 Oct 2026)
References
Other references
- https://github.com/MessagePack-CSharp/MessagePack-CSharp/security/advisories/GHSA-qhrr-8q5h-9q3h (x_refsource_CONFIRM)
- https://github.com/MessagePack-CSharp/MessagePack-CSharp/commit/7fd78bbf3476e03beae8b0f7a521125525a8a64a (x_refsource_MISC)
- https://github.com/MessagePack-CSharp/MessagePack-CSharp/commit/95b63fca4f7097d3cac12d1a95286af4b4bbf02c (x_refsource_MISC)
- https://github.com/MessagePack-CSharp/MessagePack-CSharp/releases/tag/v2.5.303 (x_refsource_MISC)
- https://github.com/MessagePack-CSharp/MessagePack-CSharp/releases/tag/v3.1.9 (x_refsource_MISC)
Other databases
Where this comes from
This advisory is generated automatically by VEDAS from: CVE.org record, cve-scores (EPSS and VEDAS). Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.