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CVE-2026-55559 critical CVSS 9.8

Code Injection in org.yamcs:yamcs-core (CVE-2026-55559)

Summary

Code injection in org.yamcs:yamcs-core (CVE-2026-55559). Successful exploitation can lead to full system takeover. Exploitable via POST /api/instances. Mitigation: upgrade to 5.12.8 or later.

Original description

The description as published by the source.

Summary

templateArgs sent to POST /api/instances (and PATCH /api/instances/{instance}) are written into the rendered instance config as raw text, then parsed as YAML and loaded. Yamcs instantiates each services: entry by its class:, so injecting YAML through a template arg lets you add a services: entry for org.yamcs.ProcessRunner and run a command on the host. The args aren't escaped for YAML or validated server-side.

Needs the CreateInstances privilege. With no security.yaml the guest user is superuser=true and the API is unauthenticated, so it's reachable without auth, same default exposure as CVE-2026-46562. The 5.12.7 algorithm-edit fix doesn't touch this path.

Details

VarStatement appends arg values with no escaping:

// yamcs-core/src/main/java/org/yamcs/templating/VarStatement.java:29
buf.append(value);

The only filter, EscapeFilter, does HTML escaping (& < > ' ") and leaves newlines, colons and indentation alone, so {{ x | escape }} doesn't help either. InstancesApi.createInstance forwards the args without checking them against the declared variables; the choices / required metadata is only used to render the web form.

Request to exec:
InstancesApi.createInstance (http/api/InstancesApi.java:169, checks CreateInstances)
→ YamcsServer.createInstance (YamcsServer.java:651, template.process(templateArgs))
→ rendered config loaded as YConfiguration
→ YamcsServerInstance instantiates services:…

Source: GitHub Security Advisories (Global) 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-2026-55559 has been found in org.yamcs:yamcs-core.
Attackers can target a specific entry point like POST /api/instances over the network to misuse the product.
Successful exploitation can lead to full system takeover. CVSS score: 9.8/10.
What to do: upgrade org.yamcs:yamcs-core to 5.12.8 or later.
If unsure, ask your IT team or search "org.yamcs:yamcs-core CVE-2026-55559" on the vendor's site.

CVE-2026-55559 (org.yamcs:yamcs-core) — CWE-94 / CVSS v3 9.8
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: POST /api/instances / PATCH /api/instances/{instance} / templateArgs / org.yamcs.ProcessRunner
Patched: 5.12.8 — 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

Arbitrary code execution (CWE-94) exists in org.yamcs:yamcs-core. Attackers reach the vulnerable code path via POST /api/instances without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of org.yamcs:yamcs-core. Attack surface: POST /api/instances / PATCH /api/instances/{instance} / templateArgs / org.yamcs.ProcessRunner.

🔥 Severity

Severity: Critical (CVSS 9.8/10). Successful exploitation can lead to full system takeover.

🔧 How to fix

Update to 5.12.8.

🛡️ 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 POST /api/instances requests with malformed payloads or SQL meta-characters. Audit SBOM/dependencies to find affected services.

Response actions

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

  1. 1
    Identify exposure identify 
    Audit SBOM/dependencies for affected components.

    資産台帳・SBOM・依存マニフェストで org.yamcs:yamcs-core を使っているサービスとバージョンを洗い出す。

  2. 2
    Hunt for indicators of compromise detect 
    grep 'POST /api/instances' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'

    アクセスログで POST /api/instances への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。

  3. 3
    Apply patch patch 
    Upgrade org.yamcs:yamcs-core to 5.12.8

    ステージング環境で 5.12.8 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と、Step 2 で見つけた異常検知の続報チェックを含めること。

  4. 4
    Post-deployment verification verify 
    Replay attack against POST /api/instances on staging to confirm patch closes the vector

    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 Step 2 と同じログクエリでアラート再発が無いか継続監視。

Affected packages

maven org.yamcs:yamcs-core
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"5.12.8"}]}]

References

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