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FrontAccounting CVE-2026-40521

| EUVDEUVD-2026-40083 HIGH
Path Traversal (CWE-22)
2026-06-29 VulnCheck GHSA-9fmm-h59x-wr53
Path Traversal RCE PHP Frontaccounting
8.7
CVSS 4.0 · Vendor: VulnCheck
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Severity by source

Vendor (VulnCheck) PRIMARY
8.7 HIGH
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
vuln.today AI
8.8 HIGH

Network-reachable upload, low complexity, but a low-privileged authenticated account is required (PR:L); web-shell write yields full host compromise so C/I/A all High; scope unchanged as impact is to the vulnerable system.

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

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Attack Vector
Network
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
X

Lifecycle Timeline

1
Analysis Generated
Jun 29, 2026 - 14:23 vuln.today

DescriptionCVE.org

FrontAccounting before 2.4.20 contains a path traversal vulnerability in the attachment upload handler that allows authenticated attackers to execute arbitrary code by uploading files with traversal sequences in the unique_name parameter. Attackers can supply path traversal sequences ../../../shell.php to write files outside the intended attachments directory into the web root, and by uploading PHP files without extension validation, achieve remote code execution as the web server user.

AnalysisAI

Remote code execution in FrontAccounting before 2.4.20 lets an authenticated user abuse the attachment upload handler to plant a PHP web shell. The handler fails to validate the unique_name parameter, so traversal sequences write attacker-controlled files outside the attachments directory and into the web root, and because file extensions are not validated, an uploaded PHP file executes as the web server user. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Recon
Authenticate with low-privilege account
Delivery
Open attachment upload feature
Exploit
Set unique_name to ../../../shell.php
Install
Submit PHP payload past extension check
C2
File written into web root
Execute
Request shell URL
Impact
Execute commands as web server user
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Vulnerability AssessmentAI

Exploitation Exploitation requires an authenticated session - the CVSS vector specifies PR:L, so a valid low-privileged FrontAccounting account is needed - plus access to the attachment upload functionality. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment Signals are largely consistent and point to a genuine, high-priority issue. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario An attacker with a low-privileged FrontAccounting login navigates to a feature that uploads an attachment and intercepts the request, setting the unique_name parameter to something like ../../../shell.php with PHP web-shell content as the body. Because the path is not sanitized and the extension is not checked, the file is written into the web root and can then be requested directly to run arbitrary commands as the web server user. …
Remediation Vendor-released patch: upgrade to FrontAccounting 2.4.20, which addresses the traversal and missing extension validation in the attachment upload handler (release notes: https://sourceforge.net/p/frontaccounting/news/2026/04/release-2420/; fix commit: https://github.com/FrontAccountingERP/FA/commit/701fea6848da4a02fb83d30f07a9c0473d6b7e33). … Detailed patch versions, workarounds, and compensating controls in full report.
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Recommended ActionAI

Within 24 hours: Inventory all FrontAccounting installations and identify instances running versions prior to 2.4.20; restrict access to attachment upload functionality. …

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Threat intelligence, references, and detailed analysis are available after sign-in.

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CVE-2026-40521 vulnerability details – vuln.today
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