CVE-2026-50659 medium CVSS 6.5

Vulnerability in Microsoft.NetCore.App.Runtime.linux-arm (CVE-2026-50659)

Summary

Vulnerability in Microsoft.NetCore.App.Runtime.linux-arm (CVE-2026-50659). Data can be tampered with by attackers. Mitigation: upgrade to 8.0.29 or later.

Original description

The description as published by the source.

Executive summary

Microsoft is releasing this security advisory to provide information about a vulnerability in .NET SMTP client (System.Net.Mail). This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

A spoofing vulnerability exists in the SMTP client implementation (System.Net.Mail) in .NET 8, .NET 9, and .NET 10, where an attacker can spoof messages during message routing.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/**TBD**

CVSS Details

Version: 3.1
Severity: Medium
Score: 6.5
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
Weakness: CWE-116 (Improper Encoding or Escaping of Output)

Affected Platforms

Platforms: All
Architectures: All

Affected Packages

The vulnerability affects any Microsoft .NET project if it uses any of affected package versions listed below

.NET 10.0

Package name	Affected version	Patched version
Microsoft.NetCore.App.Runtime.linux-arm	>= 10.0.0, <= 10.0.9	10.0.10
Microsoft.NetCore.App.Runtime.linux-arm64	>= 10.0.0, <= 10.0.9	10.0.10
[Microsoft.NetCore.App.Runtime.linux-musl-arm](https://www.nuget.org/packa…

Source: NIST National Vulnerability Database NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-50659 has been found in Microsoft.NetCore.App.Runtime.linux-arm.
Data can be tampered with by attackers. CVSS score: 6.5/10.
What to do: upgrade Microsoft.NetCore.App.Runtime.linux-arm to 8.0.29 or later.
If unsure, ask your IT team or search "Microsoft.NetCore.App.Runtime.linux-arm CVE-2026-50659" on the vendor's site.

CVE-2026-50659 (Microsoft.NetCore.App.Runtime.linux-arm) — CWE-116 / CVSS v3 6.5
Attack vector: remote (network-reachable) / no user interaction
Patched: 8.0.29 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

A vulnerability (CWE-116) exists in Microsoft.NetCore.App.Runtime.linux-arm.

📍 Affected scope

Check the vendor advisory for the affected versions of Microsoft.NetCore.App.Runtime.linux-arm.

🔥 Severity

Severity: Medium (CVSS 6.5/10). Data can be tampered with by attackers.

🔧 How to fix

Update to 8.0.29.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'Microsoft.NetCore.App.Runtime.linux-arm' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

1
Identify exposure identify
```
grep -r 'Microsoft.NetCore.App.Runtime.linux-arm' . | grep -v node_modules
```
リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で Microsoft.NetCore.App.Runtime.linux-arm を grep し、稼働しているサービス・バージョンを把握する。
2
Apply patch patch
```
Upgrade Microsoft.NetCore.App.Runtime.linux-arm to 8.0.29
```
ステージング環境で 8.0.29 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。
3
Post-deployment verification verify
```
Confirm patched version is live in production
```
パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。