# [CRIT] [GHSA / CRITICAL] CVE-2026-46621: Yamcs Vulnerable to Authenticated Remote Code Execution (RCE) via Jython Algorithm Code Injection

**Source:** GitHub Security Advisories
**Published:** 2026-05-27
**Article:** https://github.com/advisories/GHSA-2g95-6x5q-xjwj

## Threat Profile

Yamcs Vulnerable to Authenticated Remote Code Execution (RCE) via Jython Algorithm Code Injection

### Summary
A Server-Side Code Injection vulnerability exists in the Yamcs script evaluation engine for Python algorithms. The application dynamically compiles and evaluates user-controlled algorithm text using Jython (via the JSR-223 ScriptEngine API) without enforcing a secure sandbox. An authenticated user with the `ChangeMissionDatabase` privilege can exploit this by overriding the algorithm lo…

## Indicators of Compromise (high-fidelity only)

- **CVE:** `CVE-2026-46621`

## MITRE ATT&CK Techniques

- **T1190** — Exploit Public-Facing Application
- **T1021.002** — SMB/Windows Admin Shares
- **T1569.002** — Service Execution
- **T1219** — Remote Access Software
- **T1204.002** — User Execution: Malicious File
- **T1059.006** — Command and Scripting Interpreter: Python
- **T1078** — Valid Accounts
- **T1059.004** — Command and Scripting Interpreter: Unix Shell
- **T1071.001** — Application Layer Protocol: Web Protocols
- **T1105** — Ingress Tool Transfer

## Kill chain phases observed

_(none detected from narrative keywords)_

## Recommended hunts

### Yamcs MDB algorithm PATCH with embedded Jython java.lang.Runtime payload (CVE-2026-46621)

`UC_191_4` · phase: **exploit** · confidence: **High** · AI-generated for this article

**Splunk SPL (CIM):**
```spl
| tstats summariesonly=true count min(_time) as firstTime max(_time) as lastTime values(Web.url) as url values(Web.src) as src values(Web.user) as user values(Web.http_user_agent) as ua from datamodel=Web where Web.http_method=PATCH Web.url="*/api/mdb/*/realtime/algorithms/*" by Web.dest Web.url Web.src Web.user | `drop_dm_object_name(Web)` | join type=inner dest [ search index=* sourcetype=*access* method=PATCH uri_path="*/api/mdb/*/realtime/algorithms/*" ("java.lang.Runtime" OR "getRuntime" OR "import java" OR "Runtime.getRuntime" OR "exec([\"bash\"" OR "exec([\"sh\"") | stats values(uri_path) as uri_path values(http_request_body) as body by dest ] | table firstTime lastTime src user dest url ua body
```

**Defender KQL:**
```kql
// Yamcs runs as a JVM; web traffic to its REST API is usually proxied or visible as DeviceNetworkEvents to TCP/8090. Defender's HTTP-body visibility is limited — pair with the WAF/reverse-proxy log source.
DeviceNetworkEvents
| where Timestamp > ago(7d)
| where RemotePort == 8090 or LocalPort == 8090
| where InitiatingProcessFileName !in~ ("java.exe","java")
| where AdditionalFields has_any ("PATCH","/api/mdb/","/realtime/algorithms/")
| project Timestamp, DeviceName, InitiatingProcessFileName, InitiatingProcessCommandLine, RemoteIP, RemotePort, LocalPort, AdditionalFields
| order by Timestamp desc
```

### Yamcs JVM spawns shell or network utility (CVE-2026-46621 post-exploitation)

`UC_191_5` · phase: **install** · confidence: **High** · AI-generated for this article

**Splunk SPL (CIM):**
```spl
| tstats summariesonly=true count min(_time) as firstTime max(_time) as lastTime values(Processes.process) as cmdline values(Processes.process_path) as process_path values(Processes.user) as user from datamodel=Endpoint.Processes where (Processes.parent_process_name IN ("java","java.exe","jython")) AND (Processes.process_name IN ("bash","sh","dash","zsh","curl","wget","nc","ncat","python","python3","perl","powershell.exe","cmd.exe")) by Processes.dest Processes.parent_process Processes.process_name Processes.user | `drop_dm_object_name(Processes)` | where like(parent_process,"%yamcs%") OR like(parent_process,"%jython%") OR like(cmdline,"%yamcs%") OR like(cmdline,"%algorithm%") | table firstTime lastTime dest user parent_process process_name cmdline
```

**Defender KQL:**
```kql
DeviceProcessEvents
| where Timestamp > ago(7d)
| where InitiatingProcessFileName in~ ("java","java.exe","jython")
| where FileName in~ ("bash","sh","dash","zsh","curl","wget","nc","ncat","python","python3","perl","powershell.exe","cmd.exe","pwsh","pwsh.exe")
| where InitiatingProcessCommandLine has_any ("yamcs","jython","algorithm","ScriptEngine","AlgorithmManager") or InitiatingProcessFolderPath has_any ("yamcs","jython")
| project Timestamp, DeviceName, AccountName,
          ParentImage = InitiatingProcessFolderPath,
          ParentCmd   = InitiatingProcessCommandLine,
          ChildImage  = FolderPath,
          ChildCmd    = ProcessCommandLine,
          SHA256
| order by Timestamp desc
```

### Yamcs Java process beacons to webhook / interact / tunneling service (CVE-2026-46621 C2)

`UC_191_6` · phase: **c2** · confidence: **High** · AI-generated for this article

**Splunk SPL (CIM):**
```spl
| tstats summariesonly=true count min(_time) as firstTime max(_time) as lastTime values(All_Traffic.dest) as dest values(All_Traffic.dest_port) as dest_port values(All_Traffic.app) as app values(All_Traffic.process) as process values(All_Traffic.process_name) as process_name from datamodel=Network_Traffic where (All_Traffic.process_name IN ("java","java.exe","jython","curl","curl.exe","wget","wget.exe")) by All_Traffic.src All_Traffic.dest_host All_Traffic.process_name | `drop_dm_object_name(All_Traffic)` | where match(dest_host,"(?i)(webhook\.site|requestbin|interact\.sh|interactsh|oast\.fun|oast\.live|burpcollaborator\.net|ngrok\.io|ngrok-free\.app|trycloudflare\.com|beeceptor\.com|pipedream\.net|requestcatcher\.com)") | table firstTime lastTime src process_name dest_host dest_port count
```

**Defender KQL:**
```kql
let oobDomains = dynamic(["webhook.site","requestbin.com","requestbin.net","en7","interact.sh","interactsh","oast.fun","oast.live","oast.me","oast.online","oast.pro","oast.site","burpcollaborator.net","ngrok.io","ngrok-free.app","trycloudflare.com","beeceptor.com","pipedream.net","requestcatcher.com"]);
DeviceNetworkEvents
| where Timestamp > ago(7d)
| where InitiatingProcessFileName in~ ("java","java.exe","jython","curl","curl.exe","wget","wget.exe")
| where (RemoteUrl has_any (oobDomains)) or (isnotempty(AdditionalFields) and AdditionalFields has_any (oobDomains))
| project Timestamp, DeviceName, InitiatingProcessFileName, InitiatingProcessCommandLine, InitiatingProcessParentFileName, RemoteIP, RemotePort, RemoteUrl, Protocol
| order by Timestamp desc
```

### Remote service execution — PsExec / SMB lateral movement

`UC_LATERAL_PSEXEC` · phase: **actions** · confidence: **High**

**Splunk SPL (CIM):**
```spl
| tstats `summariesonly` count min(_time) as firstTime max(_time) as lastTime
    from datamodel=Endpoint.Processes
    where Processes.process_name IN ("psexec.exe","psexesvc.exe","paexec.exe","smbexec.py")
       OR (Processes.process_name="wmic.exe" AND Processes.process="*/node:*")
    by Processes.dest, Processes.user, Processes.process_name, Processes.process, Processes.parent_process_name
| `drop_dm_object_name(Processes)`
```

**Defender KQL:**
```kql
DeviceProcessEvents
| where Timestamp > ago(7d)
| where AccountName !endswith "$"
| where FileName in~ ("psexec.exe","psexesvc.exe","paexec.exe","smbexec.py")
   or (FileName =~ "wmic.exe" and ProcessCommandLine has "/node:")
| project Timestamp, DeviceName, AccountName, FileName, ProcessCommandLine, InitiatingProcessFileName
| order by Timestamp desc
```

### RMM tool installed by non-IT user — remote-access utility for hands-on-keyboard

`UC_RMM_TOOLS` · phase: **install** · confidence: **High**

**Splunk SPL (CIM):**
```spl
| tstats `summariesonly` count min(_time) as firstTime max(_time) as lastTime
    from datamodel=Endpoint.Processes
    where Processes.process_name IN ("AnyDesk.exe","TeamViewer.exe","TeamViewer_Service.exe",
        "ScreenConnect.ClientService.exe","ConnectWiseControl.ClientService.exe",
        "atera_agent.exe","SplashtopStreamer.exe","RustDesk.exe","NinjaOne.exe","kaseya*.exe")
    by Processes.dest, Processes.user, Processes.process_name, Processes.process, Processes.parent_process_name
| `drop_dm_object_name(Processes)`
```

**Defender KQL:**
```kql
DeviceProcessEvents
| where Timestamp > ago(7d)
| where AccountName !endswith "$"
| where FileName in~ ("AnyDesk.exe","TeamViewer.exe","TeamViewer_Service.exe",
        "ScreenConnect.ClientService.exe","ConnectWiseControl.ClientService.exe",
        "atera_agent.exe","SplashtopStreamer.exe","RustDesk.exe","NinjaOne.exe")
   or FileName matches regex @"(?i)kaseya.*\.exe"
| project Timestamp, DeviceName, AccountName, FileName, ProcessCommandLine
```

### Article-specific behavioural hunt — [GHSA / CRITICAL] CVE-2026-46621: Yamcs Vulnerable to Authenticated Remote Code

`UC_191_3` · phase: **exploit** · confidence: **High**

**Splunk SPL (CIM):**
```spl
``` Article-specific bespoke detection — [GHSA / CRITICAL] CVE-2026-46621: Yamcs Vulnerable to Authenticated Remote Code ```
| tstats `summariesonly` count earliest(_time) AS firstTime latest(_time) AS lastTime
    from datamodel=Endpoint.Processes
    where (Processes.process_name IN ("simulator.py"))
    by Processes.dest, Processes.user, Processes.process_name,
       Processes.process, Processes.parent_process_name, Processes.process_path
| `drop_dm_object_name(Processes)`
| `security_content_ctime(firstTime)`
| append [
| tstats `summariesonly` count
    from datamodel=Endpoint.Filesystem
    where Filesystem.action IN ("created","modified")
      AND (Filesystem.file_name IN ("simulator.py"))
    by Filesystem.dest, Filesystem.user, Filesystem.process_name,
       Filesystem.file_path, Filesystem.file_name
| `drop_dm_object_name(Filesystem)`
]
```

**Defender KQL:**
```kql
// Article-specific bespoke detection — [GHSA / CRITICAL] CVE-2026-46621: Yamcs Vulnerable to Authenticated Remote Code
// Hunts the actual binaries / paths / commandline fragments named
// in the article instead of a generic technique-class template.
DeviceProcessEvents
| where Timestamp > ago(30d)
| where (FileName in~ ("simulator.py"))
| project Timestamp, DeviceName, AccountName, FileName,
          FolderPath, ProcessCommandLine,
          InitiatingProcessFileName, InitiatingProcessCommandLine
| order by Timestamp desc

// File-creation events for the named binaries / paths
DeviceFileEvents
| where Timestamp > ago(30d)
| where ActionType in ("FileCreated","FileModified")
| where (FileName in~ ("simulator.py"))
| project Timestamp, DeviceName, AccountName, FolderPath,
          FileName, ActionType, InitiatingProcessFileName,
          InitiatingProcessCommandLine
| order by Timestamp desc
```

### IOC-driven hunts (use shared templates)

These are standard IOC-substitution hunts — the canonical SPL and KQL live once in [`_TEMPLATES.md`](../_TEMPLATES.md), so we don't repeat the same boilerplate on every CVE / hash / network-IOC briefing.

- **Asset exposure — vulnerability matches article CVE(s)** ([template](../_TEMPLATES.md#asset-exposure)) — phase: **recon**, confidence: **High**
  - CVE(s): `CVE-2026-46621`


## Why this matters

Severity classified as **CRIT** based on: CVE present, 7 use case(s) fired, 10 technique(s) inferred. Read the full article for actor attribution, tooling details, and any defanged IOCs in the body that aren't visible in the RSS summary.