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EFence CVE-2026-80235

| EUVDEUVD-2026-66344 CRITICAL
Unrestricted Upload of File with Dangerous Type (CWE-434)
2026-08-26 twcert GHSA-7xv4-f5x2-3xqj
9.3
CVSS 4.0 · Vendor: twcert
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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain

  1. Access
    Reach EFence upload endpoint over network
  2. Delivery
    Send crafted multipart file upload
  3. Exploit
    Bypass missing file-type validation
  4. Execution
    Write web shell to web-accessible path
  5. Persist
    Request shell URL to execute commands
  6. Impact
    Achieve arbitrary code execution 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

The required condition is network reachability of EFence's file upload feature - the attacker must be able to reach the upload endpoint and, for full RCE, the uploaded file must land in a location the web/application server will execute. Per the CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N), no authentication, no user interaction, and no special attack requirements are needed against a default-exposed deployment. Limiting factors that reduce real-world exposure: the vulnerability affects only EFence builds from 0 through 1.2.66 (DB Ver:56); instances not exposed to the attacker's network (internal-only or behind a VPN/allowlist) are not remotely reachable; and controls that disable script execution in the upload directory would block the code-execution step even if a file is uploaded.

Impact

The signals largely agree on high but not maximally urgent priority. The vendor-supplied CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H) scores 9.3 and describes trivial, unauthenticated, network-reachable exploitation with total impact - consistent with the SSVC assessment of Automatable:yes and Technical Impact:total. However, SSVC records Exploitation:none (no observed exploitation) and there is no CISA KEV listing and no identified public exploit, so this is not confirmed active exploitation. EPSS is moderate at 0.68% (50th percentile), which is unremarkable and reflects the absence of published exploit code rather than any technical barrier. The combination - very low technical bar and total impact, but no evidence of in-the-wild use yet - makes this a strong patch-soon candidate, especially given how readily web-shell upload flaws are weaponized once details circulate. No conflicting signals were observed; the main gap is the lack of an independently confirmed fixed version.

Exploit ScenarioDerived

A remote attacker with no account sends a crafted multipart HTTP POST to EFence's file upload endpoint, submitting a web shell disguised as or delivered as an executable server script. Because the application does not validate file type, the shell lands in a web-accessible path; the attacker then requests its URL to execute commands as the web server user, achieving full RCE. No public proof-of-concept is identified at this time, but the network attack vector and low complexity make reliable exploitation straightforward once the endpoint is known.

Act Now Prioritize within 24-48h. Why: CRITICAL severity.
No patch listed yet 0.7% exploitation probability (EPSS)

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AnalysisAIv2 – Aug 26, 2026

Unauthenticated arbitrary file upload in Thinking Software Technology's EFence (versions up to and including 1.2.66, DB Ver:56) lets remote attackers upload executable web shell backdoors and run arbitrary code on the underlying server. The flaw requires no authentication or user interaction over the network, yielding full compromise of confidentiality, integrity, and availability. Reported by TWCERT; no public exploit identified at time of analysis, and EPSS exploitation probability is moderate at 0.68% (50th percentile).

Earlier versions of this analysis (1)
v1 Aug 26, 2026 - 09:20 CVSS 9.8

Arbitrary file upload in EFence by Thinking Software Technology lets remote unauthenticated attackers upload and execute web shell backdoors, yielding full arbitrary code execution on the host. The flaw carries a critical CVSS 9.8 and was reported through Taiwan's TWCERT; no public exploit code has been identified at time of analysis. Any internet-reachable EFence instance is directly at risk since exploitation requires no credentials or user interaction.

RemediationAI

No vendor-released patch version is identified in the available data; the TWCERT advisories (https://www.twcert.org.tw/en/cp-139-11137-c6e5f-2.html and https://www.twcert.org.tw/tw/cp-132-11133-e0167-1.html) should be consulted for the vendor-supplied fixed build, since all versions through 1.2.66 (DB Ver:56) are affected. Until a fixed release is confirmed and applied, restrict network access to the EFence upload functionality - place the application behind a VPN or IP allowlist so it is not internet-exposed (trade-off: breaks remote user access). As compensating controls, deploy a WAF rule to block uploads of executable extensions (.php, .jsp, .asp, .aspx, .cgi, and double extensions) and multipart requests with script content, and configure the web/application server so the upload directory is served with execution disabled (e.g. no script handler mapping on the upload path), which prevents an uploaded shell from being interpreted (trade-off: legitimate scripted content in that path also stops running). Monitor upload directories and web logs for newly created script files and anomalous POST activity.

Affected VersionsENISA

Efence 0 ≤1.2.66 DB Ver:56

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

This is a CWE-434 Unrestricted Upload of File with Dangerous Type. The affected component, EFence, exposes a file upload endpoint that fails to validate the type, extension, or content of submitted files, allowing an attacker to place a server-executable script (a web shell) into a web-accessible directory where the application server subsequently interprets and runs it. The single CPE in scope, cpe:2.3:a:thinking_software_technology:efence:*, covers all versions of the EFence application. Because the malicious file is executed in the server's own runtime context, the class of flaw converts a simple upload weakness directly into remote code execution.

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  • Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (twcert) PRIMARY 9.3 CRITICAL
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N
vuln.today AI 9.8 CRITICAL

Unauthenticated network upload with no user interaction gives AV:N/AC:L/PR:N/UI:N; web-shell RCE yields full C:H/I:H/A:H within the server's scope.

3.1 AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
4.0 AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (twcert).

CVSS VectorVendor: twcert

Attack Vector
Network
Attack Complexity
Low
Attack Requirements
None
Privileges Required
None
User Interaction
None
Vulnerable system: Confidentiality
High
Vulnerable system: Integrity
High
Vulnerable system: Availability
High
Subsequent system: Confidentiality
None
Subsequent system: Integrity
None
Subsequent system: Availability
None

Lifecycle Timeline

2
CVSS changed
Aug 26, 2026 - 15:52 NVD
9.8 (CRITICAL) 9.3 (CRITICAL)
CVE Published
Aug 26, 2026 - 08:26 cve.org
CRITICAL 9.8

DescriptionCVE.org

EFence developed by Thinking Software Technology has an Arbitrary File Upload vulnerability. Unauthenticated remote attackers can upload and execute web shell backdoors, thereby enabling arbitrary code execution on the server.

Executive ViewAI

Why It Matters

Thinking Software Technology's EFence versions through 1.2.66 contain a critical unauthenticated file upload vulnerability allowing arbitrary code execution on affected servers. An attacker can upload and execute malicious code without credentials, potentially compromising confidentiality, integrity, and availability across all systems running this product.

Business Impact: Severe
Compensating Controls

No vendor-released patch identified at time of analysis. Deploy interim mitigations: restrict network access via firewall and network segmentation to trusted networks only, implement mandatory file upload validation and whitelist-based file type filtering, disable script execution permissions in all upload directories through web server configuration, enable detailed audit logging for upload and file access activities with alerting for anomalies, and conduct immediate log forensics for indicators of exploitation or unauthorized file presence.

Threat Intelligence Overview

EPSS Score
0.7%
Top 50% exploitable
Prevalence
Low
niche Taiwanese vendor product, limited enterprise deployment footprint
Social Media
3
Sightings
Data Quality
5 sources
Confidence: Medium

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.

SignalValue
Severity CRITICAL
CISA KEV No
Public POC No
EPSS 0.7%
Patch available No
Active threat No
Deciding rule
CRITICAL severity
What every action level means
Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.
Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.
This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.
This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.
Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision
Out-of-Cycle
Exploitation
None
System Exposure· derived
Open
Automatable
Yes
Human Impact
Very High
Technical Impact
Total

Priority Score

47
Low Medium High Critical
KEV: 0
EPSS: +1
CVSS: +46
PoC: 0
Weaponized: 0
Threat intel: 0
Gov advisory: 0

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.

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