fast-xml-builder allows attribute values with unwanted quotes to bypass malicious or unwanted attributes
# Summary When an input data has quotes in attribute values but process entities is not enabled, it breaks the attribute value into multiple attributes. This gives the room for an attacker to insert unwanted attributes to the XML/HTML. ## Detail Malicious Input ``` { a: { "@_attr": '" onClick="alert(1)' } } ``` Output ```xml ``` ### Workarounds If ...
CVSS 7.5 LOW. SENTINEL APEX recommends immediate patch evaluation. Intelligence from 1 confirmed source(s).
📋 Executive Summary
This report analyzes CVE-2026-44665 affecting npm fast-xml-builder. Composite threat score: 43/100. Intelligence corroborated across 1 source(s): github_advisories. CVSS base score: 7.5. No confirmed in-the-wild exploitation at the time of writing; prioritize on exposure, privilege, and CVSS.
⚠️ Business Impact Analysis
- ⚠️ npm fast-xml-builder users face material security risk requiring immediate remediation
🔗 Representative Attack Path
A typical attack path for this vulnerability class, mapped to MITRE ATT&CK — a representative model to guide detection and defense, not a claim of observed activity against a specific target. Confirm specifics against the primary sources below.
| # | Phase | Attacker Action | MITRE |
|---|---|---|---|
1 |
Reconnaissance | Attacker identifies exposed fast-xml-builder instances via Shodan, Censys, or targeted scanning | TA0043 |
2 |
Initial Access | Exploitation of CVE-2026-44665 in npm fast-xml-builder | 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 fast-xml-builder (CVSS 7.5) represents a significant attack surface. SENTINEL APEX assesses exploitation to be technically feasible with moderate effort. Organizations running fast-xml-builder 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 | Initial Access |
| Primary Technique | T1190 — Exploit Public-Facing Application |
| Sub-Technique | T1203 — Exploitation for Client Execution |
| Weakness (CWE) | CWE-611 |
| Intel Type | 🔴 CVE ANALYSIS |
| Source(s) | github_advisories |
🔴 CVE Reference
| CVE ID | Reference | Score |
|---|---|---|
| CVE-2026-44665 | NVD → | 7.5 |
| CVE-2026-44665 | 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 fast-xml-builder 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 fast-xml-builder 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 fast-xml-builder
📎 Intelligence References
- github.com/advisories/GHSA-5wm8-gmm8-39j9
- github.com/NaturalIntelligence/fast-xml-builder/security/advisories/GH
- github.com/advisories/GHSA-5wm8-gmm8-39j9
- 📌 NVD — CVE-2026-44665
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Report ID: SENTINEL-CVE-2026-44665-2026-05-08 | Priority: 43/100 LOW | Sources: 1
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