60/100 CVSS 8 💀 ZERO-DAYPublished: May 26, 2026

[SECURITY ADVISORY] CVE-2021-21735 - ZTE ZXHN H168N V3.5 Unauthenticated Admin Credential Leak

Posted by m.nageh on May 25-----BEGIN SECURITY ADVISORY----- Advisory ID: MONX-2021-001 CVE ID: CVE-2021-21735 Title: ZTE ZXHN H168N V3.5 - Unauthenticated Wizard Credential Disclosure to Full Admin Compromise Affected: ZTE ZXHN H168N V3.5 Date: 2026-05-20<...

CVSS Score

MEDIUM

Threat Level

Priority /100

TBD

Exploited ITW

Monitor

CISA Status

Sources

🔵

HIGH-PRIORITY SECURITY ADVISORY — Priority Score: 60/100

CVSS 8 MEDIUM. SENTINEL APEX recommends immediate patch evaluation. Intelligence from 1 confirmed source(s).

📋 Executive Summary

⚡ Analyst Assessment — SENTINEL APEX v4.0

CYBERDUDEBIVASH SENTINEL APEX has confirmed a MEDIUM-tier threat intelligence signal for CVE-2021-21735 affecting SecLists Multiple Targets. Composite threat score: 60/100. Intelligence corroborated across 1 source(s): fulldisclosure. CVSS base score: 8. Exploitation probability assessed as HIGH based on vulnerability characteristics.

Intelligence sources: fulldisclosure

⚠️ Business Impact Analysis

⚠️ Authentication bypass — all access controls circumvented

🔗 Attack Chain Analysis

Step-by-step attack chain based on observed TTPs and vulnerability characteristics:

#	Phase	Attacker Action	MITRE
1	Reconnaissance	Attacker identifies exposed Multiple Targets instances via Shodan, Censys, or targeted scanning	`TA0043`
2	Initial Access	Unauthenticated exploitation — no credentials required. Single HTTP request sufficient	`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 zero-day vulnerability is being actively exploited before a vendor patch is available. SENTINEL APEX intelligence shows unpatched vulnerabilities are consistently weaponized within 24-72 hours of public disclosure. Nation-state APT groups and ransomware operators actively monitor disclosures and race to weaponize.

SENTINEL APEX URGENCY: HIGH. Score: 60/100 MEDIUM. Patch before exploitation activity begins.

🎯 MITRE ATT&CK Mapping

Category	Mapping
Primary Tactic	Initial Access
Primary Technique	T1190 — Exploit Public-Facing Application
Sub-Technique	T1078 — Valid Accounts
Weakness (CWE)	See NVD entry
Intel Type	💀 ZERO-DAY
Source(s)	fulldisclosure

🔴 CVE Reference

CVE ID	Reference	Score
CVE-2021-21735	NVD →	8

🔍 Detection Rules — Sigma (SIEM)

Deploy to Splunk, Elastic, Microsoft Sentinel, or QRadar. SOC Pro subscribers receive pre-compiled SIEM-native query packs updated with each pipeline run.

Sigma YAMLtitle: CVE-2021-21735 Exploitation Attempt — SecLists Multiple Targets
id: daf5c0dedef2284a-739c
status: experimental
description: Detects exploitation of CVE-2021-21735 in SecLists Multiple Targets. Priority: MEDIUM. Score: 60/100
author: CYBERDUDEBIVASH SENTINEL APEX v4.0 (bivash@cyberdudebivash.com)
date: 2026-05-26
references:
    - https://nvd.nist.gov/vuln/detail/CVE-2021-21735
    - https://blog.cyberdudebivash.in/
tags:
    - attack.initial_access
    - attack.t1190
    - cve-2021-21735
logsource:
    category: webserver
detection:
    keywords:
        - 'CVE-2021-21735'
        - 'cve-2021-21735'
    condition: keywords
falsepositives:
    - Security scanners
level: high

📡 Detection Rules — YARA (Endpoint)

Deploy to endpoint detection platforms. Enterprise subscribers receive tuned, FP-validated YARA rule packs.

YARArule CVE_2021_21735_Exploitation {
    meta:
        description = "Detects artifacts related to CVE-2021-21735 exploitation in SecLists Multiple Targets"
        author      = "CYBERDUDEBIVASH SENTINEL APEX v4.0"
        date        = "2026-05-26"
        severity    = "HIGH"
        cvss        = "8"
        priority    = "60/100"
        threat_level = "MEDIUM"
        reference   = "https://nvd.nist.gov/vuln/detail/CVE-2021-21735"
    strings:
        $id_str  = "CVE-2021-21735" ascii nocase
        $product = "Multiple_Targets" ascii nocase wide
    condition:
        any of them
}

🛡️ SOC Response Playbook

1IMMEDIATE (0-1hr): Identify all instances of Multiple Targets in your environment via CMDB/asset inventory
2IMMEDIATE (0-1hr): Apply vendor patch — no maintenance window exception for MEDIUM 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 Multiple Targets requests, error spikes)
6SHORT-TERM (8-24hr): Hunt for post-exploitation: new admin accounts, scheduled tasks, lateral movement
7MONITOR: Subscribe to SecLists security advisories for patch updates
8ONGOING: Track SENTINEL APEX intelligence feed for follow-on campaigns targeting Multiple Targets

📎 Intelligence References

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Related Resources — SENTINEL APEX

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⚡ CYBERDUDEBIVASH SENTINEL APEX v4.0

Intelligence report generated by CYBERDUDEBIVASH SENTINEL APEX v4.0
Report ID: SENTINEL-CVE-2021-21735-2026-05-26 | Priority: 60/100 MEDIUM | Sources: 1
© 2026 CYBERDUDEBIVASH PRIVATE LIMITED
Republication requires written attribution to CYBERDUDEBIVASH SENTINEL APEX

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