Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessObtain valid low-privilege EFence credentials
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DeliveryCraft upload request containing web shell file
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ExploitSubmit request to EFence upload endpoint
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ExecutionServer stores executable web shell without restriction
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PersistAttacker sends HTTP request to uploaded shell URL
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ImpactExecute arbitrary OS commands on server
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2025 - Insecure Design
ASVS 5.0
V5 - File Handling File type validation, storage isolation
MITRE ATT&CK
2 techniques across 2 tactics: Command and Control, Persistence The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | Exploitation requires valid credentials to the EFence application at a low-privilege level (CVSS PR:L confirmed). No special non-default configuration or specific deployment mode is described as a prerequisite - any authenticated EFence user on versions 1.2.66 or earlier with access to the upload feature falls within the attack surface. Key limiting factors: authentication is mandatory, which prevents unauthenticated internet-wide scanning; SSVC rates automatable as 'no,' indicating the attack likely requires manual interaction or per-target knowledge rather than fully automated worm-style exploitation; and the product's regional deployment limits the pool of potential targets. Exploitation is limited to the EFence web server's process privilege context, with no subsequent system scope change indicated (SC:N/SI:N/SA:N in CVSS 4.0). |
| Impact | The CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H) confirms network accessibility with low attack complexity and no special attack requirements, requiring only low-privilege authentication. SSVC rates technical impact as total, consistent with full server compromise via web shell execution. However, SSVC also rates current exploitation as none and automatable as no, and EPSS stands at just 0.60% (46th percentile), indicating low probability of observed exploitation in the near term - likely due to EFence's limited global deployment footprint and the authentication prerequisite that prevents mass automated scanning. This is a high-severity vulnerability in terms of technical impact if the authentication barrier is cleared, but real-world risk is moderated by the PR:L requirement and the product's regional deployment base. No KEV listing and no public POC further support a current low-urgency exploitation posture, though internal or targeted attackers with valid credentials represent a credible threat. |
| Exploit ScenarioDerived | An attacker who has obtained or guessed valid low-privilege EFence credentials - through credential stuffing, phishing, or insider access - sends a crafted HTTP upload request to EFence's upload endpoint, submitting a web shell script disguised or unrestricted by the application's validation logic. Once uploaded, the attacker directly requests the web shell's URL to execute arbitrary operating system commands with the permissions of the EFence web server process. No public proof-of-concept exploit has been identified at time of analysis, but the attack pattern is well-understood for CWE-434 vulnerabilities. |
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Alert meAnalysisAIv2 – Aug 26, 2026
Arbitrary file upload in EFence (Thinking Software Technology) versions 1.2.66 and earlier allows authenticated remote attackers to upload web shell backdoors and achieve full arbitrary code execution on the underlying server. The CVSS 4.0 score of 8.7 reflects network-accessible exploitation requiring only low-privilege credentials, with confirmed total technical impact per SSVC. No public exploit has been identified at time of analysis and SSVC rates current exploitation as none, though the Taiwan CERT (TWCERT) has published advisories indicating confirmed vendor awareness.
Earlier versions of this analysis (1)
Arbitrary file upload in EFence by Thinking Software Technology enables authenticated remote attackers to upload web shell backdoors and achieve full remote code execution on the underlying server. All versions are affected per the CPE wildcard, and the CVSS 8.8 score reflects high confidentiality, integrity, and availability impact with only low-privilege authentication required. No public exploit code or CISA KEV listing has been identified at time of analysis, though the straightforward CWE-434 class and RCE tags signal high exploitability once credentials are obtained.
RemediationAI
Consult the TWCERT advisories at https://www.twcert.org.tw/tw/cp-132-11133-e0167-1.html and https://www.twcert.org.tw/en/cp-139-11137-c6e5f-2.html for vendor-issued patch guidance; a specific patched release version is not independently confirmed in the available data, so contacting Thinking Software Technology directly for the updated build is recommended. As compensating controls pending patching: restrict access to EFence's file upload functionality to the minimum required set of administrator accounts, reducing the pool of credentials that could be abused. Implement server-side enforcement of allowed file types using both extension filtering and MIME type validation at the application layer. Deploy web application firewall rules to detect and block common web shell signatures in upload requests. Monitor upload destination directories for unexpected executable file types and alert on any server-side script execution originating from those paths. Note that restricting upload access may impact legitimate workflows if users rely on it for routine operations.
Affected VersionsENISA
Affects your stack
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Technical ContextAI · show details
EFence is a network security product developed by Thinking Software Technology, a Taiwan-based vendor. The vulnerability is rooted in CWE-434 (Unrestricted Upload of File with Dangerous Type), a class of flaw where server-side file upload handlers fail to adequately validate or restrict the type, extension, or content of uploaded files. This allows an attacker to upload server-executable scripts (e.g., PHP or ASP web shells) that the web server subsequently executes as application code. The affected CPE - cpe:2.3:a:thinking_software_technology:efence:*:*:*:*:*:*:*:* - covers all versions through 1.2.66 DB Ver:56 per EUVD-2026-66346. The attack surface is the application's file upload endpoint, accessible over the network.
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Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
Network-accessible upload endpoint exploitable with low-privilege credentials; no scope change per CVSS 4.0 SC:N metrics; full C/I/A from arbitrary web shell execution.
Primary rating from Vendor (twcert).
CVSS VectorVendor: twcert
Lifecycle Timeline
2DescriptionCVE.org
EFence developed by Thinking Software Technology has an Arbitrary File Upload vulnerability. Authenticated remote attackers can upload and execute web shell backdoors, thereby enabling arbitrary code execution on the server.
Executive ViewAI
EFence versions 1.2.66 and earlier contain an arbitrary file upload vulnerability allowing authenticated users with low-privilege credentials to execute arbitrary code on affected servers, resulting in complete system compromise. This poses a critical threat to any organization deploying vulnerable EFence instances, enabling attackers to establish persistent backdoors and access sensitive data.
Disable file upload functionality if operationally feasible; restrict user access to EFence to essential personnel only; enforce network segmentation isolating EFence from sensitive systems; implement file integrity monitoring and anomalous upload detection; audit existing file repositories for unauthorized or suspicious files; establish compensating logging to track user authentication and file operations.
Threat Intelligence Overview
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Malicious file upload attacks exploit insufficient validation when web applications accept user-provided files.
Remote Code Execution represents the critical moment when an attacker successfully runs arbitrary code on a target system without physical access.
Thinking Software Efence login function has insufficient validation for user input. Rated critical severity (CVSS 9.8),
Efence login function has insufficient validation for user input. Rated critical severity (CVSS 9.8), this vulnerability
Unauthenticated arbitrary file upload in Thinking Software Technology's EFence (versions up to and including 1.2.66, DB
SQL injection in Thinking Software Technology's Efence (versions ≤ 1.2.66 DB Ver:56) exposes full database contents to u
Unauthenticated SQL injection in EFence (Thinking Software Technology) exposes full database read access to remote attac
Multiple cross-site scripting (XSS) vulnerabilities in callback.php in the efence plugin 1.3.2 and earlier for WordPress
EUVD-2026-66346
GHSA-5w42-7c8c-6jj3
NVD
CVE.org
EPSS
Vulnrichment
Exploit-DB