flat-to-nested: Prototype pollution in flat-to-nested convert() via __proto__ parent/id key
### Summary `convert()` builds the nested tree by using each flat record's `id` and `parent` field values directly as object keys, with no guard against `__proto__` / `constructor` / `prototype`. A record whose `parent` is the string `"__proto__"` makes `temp[parent]` resolve to `Object.prototype`, and the following `initPush(...)` writes attacker-...
CVSS 7.5 LOW. SENTINEL APEX recommends immediate patch evaluation. Intelligence from 1 confirmed source(s).
📋 Executive Summary
CYBERDUDEBIVASH SENTINEL APEX has confirmed a LOW-tier threat intelligence signal for CVE-2026-55091 affecting npm flat-to-nested. Composite threat score: 43/100. Intelligence corroborated across 1 source(s): github_advisories. CVSS base score: 7.5. Exploitation probability assessed as HIGH based on vulnerability characteristics.
⚠️ Business Impact Analysis
- ⚠️ npm flat-to-nested users face material security risk requiring immediate remediation
🔗 Attack Chain Analysis
Step-by-step attack chain based on observed TTPs and vulnerability characteristics:
| # | Phase | Attacker Action | MITRE |
|---|---|---|---|
1 |
Reconnaissance | Attacker identifies exposed flat-to-nested instances via Shodan, Censys, or targeted scanning | TA0043 |
2 |
Initial Access | Exploitation of CVE-2026-55091 in npm flat-to-nested | T1190 |
3 |
Persistence | Backdoor, scheduled task, or new admin account created for persistent access | T1053 |
4 |
Command & Control | Attacker establishes persistent C2 channel using HTTPS or DNS tunneling | T1071 |
5 |
Impact / Objectives | Intellectual property theft, espionage, cryptomining, or preparation for future attack stage | T1657 |
⚠ Deep Dive Analysis
This high-severity vulnerability in npm flat-to-nested (CVSS 7.5) represents a significant attack surface. SENTINEL APEX assesses exploitation to be technically feasible with moderate effort. Organizations running flat-to-nested in internet-facing or privileged positions face immediate risk.
SENTINEL APEX URGENCY: ELEVATED. Score: 43/100 LOW. Patch before exploitation activity begins.
🎯 MITRE ATT&CK Mapping
| Category | Mapping |
|---|---|
| Primary Tactic | ML Attack Staging |
| Primary Technique | AML.T0040 — ML Attack Staging |
| Sub-Technique | AML.T0000 — AI/ML System Enumeration |
| Weakness (CWE) | CWE-915 |
| Intel Type | 🔴 CVE ANALYSIS |
| Source(s) | github_advisories |
🔴 CVE Reference
| CVE ID | Reference | Score |
|---|---|---|
| CVE-2026-55091 | NVD → | 7.5 |
| CVE-2026-55091 | NVD → | 7.5 |
🔍 Detection Rules — Sigma (SIEM)
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📡 Detection Rules — YARA (Endpoint)
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🛡️ SOC Response Playbook
- 1IMMEDIATE (0-1hr): Identify all instances of flat-to-nested in your environment via CMDB/asset inventory
- 2IMMEDIATE (0-1hr): Apply vendor patch — no maintenance window exception for LOW threats
- 3IMMEDIATE (1-2hr): If no patch available: implement WAF rules, ACLs, or network-level compensating controls
- 4SHORT-TERM (2-4hr): Deploy Sigma detection rule to SIEM — validate alert generation in test environment
- 5SHORT-TERM (4-8hr): Review logs for exploitation indicators (anomalous flat-to-nested requests, error spikes)
- 6SHORT-TERM (8-24hr): Hunt for post-exploitation: new admin accounts, scheduled tasks, lateral movement
- 7MONITOR: Subscribe to npm security advisories for patch updates
- 8ONGOING: Track SENTINEL APEX intelligence feed for follow-on campaigns targeting flat-to-nested
📎 Intelligence References
- github.com/advisories/GHSA-hp36-v28f-w3r4
- github.com/joaonuno/flat-to-nested-js/security/advisories/GHSA-hp36-v2
- github.com/joaonuno/flat-to-nested-js/commit/680a5ebe1194edda16fa93baa
- github.com/advisories/GHSA-hp36-v28f-w3r4
- 📌 NVD — CVE-2026-55091
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Report ID: SENTINEL-CVE-2026-55091-2026-06-19 | Priority: 43/100 LOW | Sources: 1
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