CVE-2026-62899 medium CVSS 5.9

Vulnerability in Microsoft.NETCore.App.Runtime.linux-arm (CVE-2026-62899)

Summary

Vulnerability in Microsoft.NETCore.App.Runtime.linux-arm (CVE-2026-62899). Confidential information can be exposed externally. Mitigation: upgrade to 8.0.30 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 System.Net.HttpListener. This advisory also provides guidance on what developers can do to update their applications to remove this vulnerability.

Inconsistent interpretation of http requests ('http request/response smuggling') in .NET allows an unauthorized attacker to bypass a security feature over a network.

Announcement

Announcement for this issue can be found at https://github.com/dotnet/announcements/issues/427

CVSS Details

Version: 3.1
Severity: Medium
Score: 5.9
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N/E:U/RL:O/RC:C
Weakness: CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')

Affected Platforms

Platforms: Linux, macOS
Architectures: All

Affected Packages

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

.NET 10

Package name	Affected version	Patched version
Microsoft.NETCore.App.Runtime.linux-arm	>= 10.0.0, <= 10.0.10	10.0.11
Microsoft.NETCore.App.Runtime.linux-arm64	>= 10.0.0, <= 10.0.10	10.0.11
[Microsoft.NETCore.App.Runtime.linux-musl-arm](https://www.nuget.…

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-2026-62899 has been found in Microsoft.NETCore.App.Runtime.linux-arm.
Confidential information can be exposed externally. CVSS score: 5.9/10.
What to do: upgrade Microsoft.NETCore.App.Runtime.linux-arm to 8.0.30 or later.
If unsure, ask your IT team or search "Microsoft.NETCore.App.Runtime.linux-arm CVE-2026-62899" on the vendor's site.

CVE-2026-62899 (Microsoft.NETCore.App.Runtime.linux-arm) — CWE-444 / CVSS v3 5.9
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 8.0.30 — 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-444) 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 5.9/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 8.0.30.

🛡️ 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 8.0.30
```
ステージング環境で 8.0.30 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。