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Fencer Vulns
medium 5.3

CVE-2026-92707 json

MessagePack: Nested arrays can blow past buffer length limits

published 2026-10-15 24 d ago modified 2026-10-16 23 d ago also GHSA-qhrr-8q5h-9q3h , EUVD-2026-102315

cvss
5.3
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.7%
EPSS 0.7% chance of exploitation in 30 days, percentile 52%
public exploits
0
none known

Summary

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.

Patch / fix

  • nuget MessagePack 2.5.303, 3.1.9
  • dotnet8 Ubuntu 22.04 LTS 8.0.132-8.0.32-0ubuntu1~22.04.1
  • dotnet8 Ubuntu 24.04 LTS 8.0.132-8.0.32-0ubuntu1~24.04.1
  • dotnet10 Ubuntu 24.04 LTS 10.0.113-10.0.13-0ubuntu1~24.04.1
  • dotnet10 Ubuntu 26.10 10.0.113-10.0.13-0ubuntu1~26.10.1
  • dotnet10 Ubuntu 26.04 LTS 10.0.113-10.0.13-0ubuntu1~26.04.1
  • dotnet11 Ubuntu 26.10 11.0.100-11.0.0~rc2-0ubuntu1~26.10.1

ubuntu advisories UBUNTU-CVE-2026-92707

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

  • dotnet-sdk-8.0 AlmaLinux 8 8.0.132-2.el8_10
  • dotnet-hostfxr-8.0 AlmaLinux 8 8.0.32-2.el8_10
  • dotnet-runtime-8.0 AlmaLinux 8 8.0.32-2.el8_10
  • dotnet-sdk-dbg-8.0 AlmaLinux 8 8.0.132-2.el8_10
  • dotnet-templates-8.0 AlmaLinux 8 8.0.132-2.el8_10
  • aspnetcore-runtime-8.0 AlmaLinux 8 8.0.32-2.el8_10
  • dotnet-runtime-dbg-8.0 AlmaLinux 8 8.0.32-2.el8_10
  • dotnet-apphost-pack-8.0 AlmaLinux 8 8.0.32-2.el8_10

almalinux advisories ALSA-2026:86594ALSA-2026:86168ALSA-2026:86169ALSA-2026:86170ALSA-2026:86171ALSA-2026:86172

  • dotnet8.0 Rocky Linux 10 8.0.132-1.el10_2
  • dotnet9.0 Rocky Linux 10 9.0.122-1.el10_2
  • dotnet10.0 Rocky Linux 10 10.0.113-1.el10_2
  • dotnet8.0 Rocky Linux 9 8.0.132-1.el9_8
  • dotnet9.0 Rocky Linux 9 9.0.122-1.el9_8
  • dotnet10.0 Rocky Linux 9 10.0.113-1.el9_8
  • dotnet9.0 Rocky Linux 8 9.0.122-1.el8_10
  • dotnet10.0 Rocky Linux 8 10.0.113-1.el8_10

rocky linux advisories RLSA-2026:86168RLSA-2026:86172RLSA-2026:86195RLSA-2026:86169RLSA-2026:86171RLSA-2026:86193

  • dotnet8-runtime Alpine 3.24, Alpine 3.23, Alpine 3.22 8.0.32-r0
  • dotnet9-runtime Alpine 3.24, Alpine 3.23, Alpine 3.22 9.0.21-r0
  • dotnet10-runtime Alpine 3.24, Alpine 3.23 10.0.13-r0

alpine advisories ALPINE-CVE-2026-92707

Alpine secdb © Alpine Linux, from https://secdb.alpinelinux.org via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2026-92707 updated cvss 5.3

dotnet10.0: dotnet8.0: dotnet9.0: dotnet: MessagePack: Nested arrays can blow past buffer length limits

  • Red Hat CodeReady Linux Builder EUS (v.9.6) dotnet-sdk-8.0-source-built-artifacts 8.0.132-1.el9_6, dotnet-sdk-9.0-source-built-artifacts 9.0.122-1.el9_6
    fixed: vendor fix RHSA-2026:88422
  • Red Hat Enterprise Linux AppStream (v. 8) dotnet 10.0.113-1.el8_10, dotnet8.0 8.0.132-2.el8_10, dotnet9.0 9.0.122-1.el8_10, dotnet10.0 10.0.113-1.el8_10, dotnet-sdk-8.0 8.0.132-2.el8_10, dotnet-sdk-9.0 9.0.122-1.el8_10, +34 more
    fixed: vendor fix RHSA-2026:86192
  • Red Hat Enterprise Linux AppStream (v. 9) dotnet8.0 8.0.132-1.el9_8, dotnet9.0 9.0.122-1.el9_8, dotnet-host 10.0.13-1.el9_8, dotnet10.0 10.0.113-1.el9_8, dotnet-sdk-8.0 8.0.132-1.el9_8, dotnet-sdk-9.0 9.0.122-1.el9_8, +34 more
    fixed: vendor fix RHSA-2026:86193
  • Red Hat Enterprise Linux AppStream (v. 10) dotnet8.0 8.0.132-1.el10_2, dotnet9.0 9.0.122-1.el10_2, dotnet-host 10.0.13-1.el10_2, dotnet10.0 10.0.113-1.el10_2, dotnet-sdk-8.0 8.0.132-1.el10_2, dotnet-sdk-9.0 9.0.122-1.el10_2, +34 more
    fixed: vendor fix RHSA-2026:86195
  • Red Hat Enterprise Linux AppStream E4S (v.9.4) dotnet8.0 8.0.132-1.el9_4, dotnet-host 8.0.32-1.el9_4, dotnet-sdk-8.0 8.0.132-1.el9_4, dotnet-hostfxr-8.0 8.0.32-1.el9_4, dotnet-runtime-8.0 8.0.32-1.el9_4, dotnet-sdk-dbg-8.0 8.0.132-1.el9_4, +8 more
    fixed: vendor fix RHSA-2026:88425
  • Red Hat Enterprise Linux AppStream EUS (v. 10.0) dotnet8.0 8.0.132-1.el10_0, dotnet9.0 9.0.122-1.el10_0, dotnet-host 9.0.21-1.el10_0, dotnet-sdk-8.0 8.0.132-1.el10_0, dotnet-sdk-9.0 9.0.122-1.el10_0, dotnet-hostfxr-8.0 8.0.32-1.el10_0, +21 more
    fixed: vendor fix RHSA-2026:88474
  • Red Hat Enterprise Linux AppStream EUS (v.9.6) dotnet8.0 8.0.132-1.el9_6, dotnet9.0 9.0.122-1.el9_6, dotnet-host 9.0.21-1.el9_6, dotnet-sdk-8.0 8.0.132-1.el9_6, dotnet-sdk-9.0 9.0.122-1.el9_6, dotnet-hostfxr-8.0 8.0.32-1.el9_6, +21 more
    fixed: vendor fix RHSA-2026:88422
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) dotnet-sdk-8.0-source-built-artifacts 8.0.132-1.el9_8, dotnet-sdk-9.0-source-built-artifacts 9.0.122-1.el9_8, dotnet-sdk-10.0-source-built-artifacts 10.0.113-1.el9_8
    fixed: vendor fix RHSA-2026:86193
show 4 more
  • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) dotnet-sdk-8.0-source-built-artifacts 8.0.132-1.el10_2, dotnet-sdk-9.0-source-built-artifacts 9.0.122-1.el10_2, dotnet-sdk-10.0-source-built-artifacts 10.0.113-1.el10_2
    fixed: vendor fix RHSA-2026:86195
  • Red Hat Enterprise Linux CodeReady Linux Builder EUS (v. 10.0) dotnet-sdk-8.0-source-built-artifacts 8.0.132-1.el10_0, dotnet-sdk-9.0-source-built-artifacts 9.0.122-1.el10_0
    fixed: vendor fix RHSA-2026:88474
  • Red Hat Enterprise Linux CRB (v. 8) dotnet-sdk-8.0-source-built-artifacts 8.0.132-2.el8_10, dotnet-sdk-9.0-source-built-artifacts 9.0.122-1.el8_10, dotnet-sdk-10.0-source-built-artifacts 10.0.113-1.el8_10
    fixed: vendor fix RHSA-2026:86192
  • Red Hat Hardened Images dotnet10.0 10.0.112-1.hum1, dotnet8.0 8.0.131-0.1.hum1, dotnet9.0 9.0.121-0.1.hum1
    not affected: component not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
24 d ago

Exploit prediction

0.68% chance of exploitation in the next 30 days, higher than 52% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
GitHub 3.1 5.3 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L

Affected packages

ecosystem package affected fixed in
nuget MessagePack
<2.5.303
>=3.0.0, <3.1.9
2.5.303
3.1.9

Affected products

  • MessagePack-CSharp MessagePack-CSharp

Classification

Weakness
  • CWE-1325 Improperly Controlled Sequential Memory Allocation

References

Sources

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.