Skip to content
Fencer Vulns
high 7.5

CVE-2026-21218 json

.NET Spoofing Vulnerability

published 2026-02-10 8 mo ago modified 2026-09-10 1 mo ago also BIT-dotnet-2026-21218 , BIT-dotnet-sdk-2026-21218 , EUVD-2026-7347 , GHSA-qvhc-9v3j-5rfw

cvss
7.5
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
1.0%
EPSS 1.0% chance of exploitation in 30 days, percentile 62%
public exploits
0
none known

Summary

Improper handling of missing special element in .NET allows an unauthorized attacker to perform spoofing over a network.

Patch / fix

  • nuget System.Security.Cryptography.Cose 8.0.2, 9.0.13, 10.0.3
  • bitnami dotnet 8.0.24, 9.0.13, 10.0.3
  • bitnami dotnet-sdk 8.0.24, 9.0.13, 10.0.3
  • Microsoft .NET 10.0 10.0.3
  • Microsoft .NET 8.0 8.0.24
  • Microsoft .NET 9.0 9.0.13
  • dotnet8 Ubuntu 22.04 LTS 8.0.124-8.0.24-0ubuntu1~22.04.1
  • dotnet8 Ubuntu 24.04 LTS 8.0.124-8.0.24-0ubuntu1~24.04.1
  • dotnet8 Ubuntu 25.10 8.0.124-8.0.24-0ubuntu1~25.10.1
  • dotnet9 Ubuntu 25.10 9.0.114-9.0.13-0ubuntu1~25.10.1
  • dotnet10 Ubuntu 24.04 LTS 10.0.103-10.0.3-0ubuntu1~24.04.1
  • dotnet10 Ubuntu 25.10 10.0.103-10.0.3-0ubuntu1~25.10.1

ubuntu advisories UBUNTU-CVE-2026-21218

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

  • dotnet8-runtime Alpine 3.24, Alpine 3.23, Alpine 3.22 +2 more 8.0.24-r0
  • dotnet9-runtime Alpine 3.24, Alpine 3.23, Alpine 3.22 +1 more 9.0.13-r0
  • dotnet10-runtime Alpine 3.24, Alpine 3.23 10.0.3-r0

alpine advisories ALPINE-CVE-2026-21218

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

CISA SSVC

Exploitation
none
Automatable
yes
Technical impact
partial
Assessed
8 mo ago

Exploit prediction

1.00% chance of exploitation in the next 30 days, higher than 62% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by version score vector
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N/E:U/RL:O/RC:C
CNA 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N
OSV 3.1 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

Affected packages

ecosystem package affected fixed in
nuget System.Security.Cryptography.Cose
>=8.0.0, <8.0.2
>=9.0.0, <9.0.13
>=10.0.0, <10.0.3
8.0.2
9.0.13
10.0.3
bitnami dotnet
>=8.0.0, <8.0.24
>=9.0.0, <9.0.13
>=10.0.0, <10.0.3
8.0.24
9.0.13
10.0.3
bitnami dotnet-sdk
>=8.0.0, <8.0.24
>=9.0.0, <9.0.13
>=10.0.0, <10.0.3
8.0.24
9.0.13
10.0.3

Affected products

  • Microsoft .NET 10.0
  • Microsoft .NET 8.0
  • Microsoft .NET 9.0

Classification

Weakness
  • CWE-166 Improper Handling of Missing Special Element

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.