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How CVE-2026-49252 Works
deepstream.io is a real‑time data synchronization server that allows clients and backend services to sync data, send messages, and execute RPCs at scale. Versions prior to 10.0.5 are vulnerable to a prototype pollution flaw (CWE‑1321).
The vulnerability stems from inadequate input sanitization in the server’s data processing pipeline. When an authenticated user with write permission sends a record update, the server merges the incoming JSON payload into existing record objects without properly filtering dangerous prototype‑modifying keys. An attacker can craft a payload that includes special paths such as __proto__, constructor, or prototype. Because deepstream uses JavaScript’s object merging logic internally, these keys allow the attacker to pollute the global Object.prototype.
Once the prototype is polluted, every subsequent object created in the server process inherits the injected properties. This can lead to privilege escalation: a low‑privileged user with only write access to any record can inject properties that alter the server’s internal authorization checks, bypass permission models, or even execute arbitrary code if the polluted property triggers a dangerous code path. The attack requires no user interaction, is exploitable over the network, and has a low attack complexity.
The issue was discovered and reported through GitHub’s security advisory system (GHSA‑9v98‑6g37‑x9g6). The patch, released in version 10.0.5, sanitizes all incoming messages by filtering out any keys that match __proto__, constructor, or `prototype` before they reach the server’s message pipeline. Administrators are strongly advised to upgrade immediately or apply the workaround of blocking such messages at the network or application level.
DailyCVE Form:
Platform: ……. deepstream.io
Version: …….. < 10.0.5
Vulnerability: .. Prototype Pollution (CWE‑1321)
Severity: ……. CRITICAL (CVSS 9.9)
date: ……….. 2026‑06‑18
Prediction: ….. Patch expected 2026‑06‑20
What Undercode Say: Analytics
Check current deepstream version npm list deepstream.io Verify if running a vulnerable version (< 10.0.5) deepstream --version Monitor logs for suspicious <strong>proto</strong> or constructor patterns grep -E "<strong>proto</strong>|constructor|prototype" /var/log/deepstream/.log Count potentially malicious messages in the last hour grep -cE "<strong>proto</strong>|constructor|prototype" /var/log/deepstream/access.log
Detection rule (Suricata/Snort):
alert tcp any any -> any any (msg:"deepstream prototype pollution attempt"; content:"<strong>proto</strong>"; nocase; sid:1000001; rev:1;)
CVE timeline analytics:
- Published (NVD): 2026‑06‑18
- GitHub Advisory published: 2026‑06‑26
- CVSS Vector: AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:L
- EPSS: Not yet available
- Confidence: High (0.7617)
Exploit
A malicious authenticated user can send a record update with a polluted payload:
// Example malicious payload sent via deepstream client
const maliciousPayload = {
"<strong>proto</strong>": {
"isAdmin": true,
"bypassAuth": function() { return true; }
}
};
// Send as a record update
client.record.setData('someRecord', maliciousPayload);
When the server merges this into its internal objects, `Object.prototype.isAdmin` becomes `true` for all objects, potentially granting the attacker elevated privileges.
Manual exploit simulation (Node.js):
const polluted = JSON.parse('{"<strong>proto</strong>": {"polluted": true}}');
Object.assign({}, polluted);
console.log({}.polluted); // true — prototype polluted
Crafting a path‑based pollution:
// Using deepstream's record path update
client.record.set('someRecord.path.to.<strong>proto</strong>.admin', true);
Protection
1. Upgrade to deepstream.io v10.0.5 or later immediately.
- Workaround – filter all messages containing
__proto__,constructor, or `prototype` before they reach the server’s message pipeline.
Example middleware (Node.js):
const sanitize = (msg) => {
const blocked = ['<strong>proto</strong>', 'constructor', 'prototype'];
const sanitized = JSON.stringify(msg, (key, val) => {
if (blocked.includes(key)) return undefined;
return val;
});
return JSON.parse(sanitized);
};
3. Restrict write permissions for authenticated users to only essential records.
4. Enable request validation at the reverse proxy level (Nginx/Apache) to drop requests containing dangerous keys.
5. Monitor server logs for any occurrences of __proto__, constructor, or `prototype` in incoming messages.
Impact
- Confidentiality: HIGH – attacker can read any data by polluting prototype properties that bypass access controls.
- Integrity: HIGH – attacker can modify any record or server state.
- Availability: LOW – potential for denial‑of‑service through property injection.
- Privilege Escalation: any authenticated user with write permission to any record can escalate to full administrative control.
- Scope: CHANGED – the vulnerable component impacts resources beyond its original security scope.
- Attack Vector: NETWORK – remotely exploitable over the network.
- User Interaction: NONE – no user action required beyond the attacker’s own authenticated session.
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Sources:
Reported By: github.com
Extra Source Hub:
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