8.2

CVSS Score

3.1

-

CVSS Score

Basic Information

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CVE-2026-45089

CVE-2026-45089: Dalfox: Unauthenticated Arbitrary File Create/Append via `output` Option in Dalfox Server Mode

Dalfox is a powerful open-source XSS scanner and utility focused on automation. Prior to 2.13.0, when dalfox is run in REST API server mode, the output, output-all, and debug fields in model.Options are JSON-tagged and deserialized directly from the attacker's request body, then propagated unchanged through dalfox.Initialize into the scan engine's logging path. The logger opens the attacker-supplied path with os.O_APPEND|os.O_CREATE|os.O_WRONLY and writes scan log lines to it. Critically, this file write block lives outside the IsLibrary guard in DalLog, so it executes even in server/library mode where file output was never intended to operate. Because no API key is required in the default configuration, an unauthenticated network caller can create or append to any file writable by the dalfox process on the host filesystem. This vulnerability is fixed in 2.13.0.

(GitHub Advisory)

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CVE-2026-45089

CVE-2026-45089:

8.2

CVSS Score

3.1

-

CVSS Score

Basic Information

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Technical Details

Package Name	Ecosystem	Vulnerable Versions	First Patched Version
github.com/hahwul/dalfox/v2	go	<= 2.12.0	2.13.0

Technical Details

Vulnerability Intelligence
Miggo AI

Root Cause Analysis

The vulnerability is an unauthenticated arbitrary file write in Dalfox's server mode. The root cause is twofold: first, the API handlers (server.postScanHandler for the REST API and an anonymous function in server.RunMCPServer for the MCP API) accepted and processed user-supplied options from a JSON request without proper sanitization. An attacker could specify an arbitrary file path in the output field of the request. Second, the logging function printing.DalLog contained a logic flaw where it would write to the specified file path regardless of whether it was running in a server context (where file I/O should be disabled).

During exploitation, an unauthenticated attacker sends a crafted POST request to the /scan endpoint. The vulnerable handler server.postScanHandler passes the malicious file path to the scan engine. Eventually, the printing.DalLog function is called, which proceeds to open and append to the attacker-specified file on the host filesystem. The patch mitigates this by introducing sanitizeAPIScanOptions, a function that strips dangerous filesystem-related options like OutputFile at the API boundary, preventing the malicious input from ever reaching the vulnerable logging function.

Vulnerable functions

server.postScanHandler

pkg/server/server.go

This function serves as the HTTP handler for the '/scan' endpoint in the REST API server. It was vulnerable because it directly deserialized the JSON request body, including attacker-controlled 'output', 'output-all', and 'debug' options, into the scan options. These unsanitized options, containing a malicious file path, were then passed to the scanning engine, leading to an arbitrary file write. The vulnerability was the failure to sanitize this input.

printing.DalLog

internal/printing/logger.go

This function acts as the vulnerability's sink. It receives the options object and is responsible for writing log messages. It contains a logic flaw where it opens and writes to the file specified in `options.OutputFile` without checking the `IsLibrary` flag, which is meant to prevent file I/O in server mode. This unconditional file write operation is what an attacker exploits to create or append to arbitrary files on the filesystem.

server.RunMCPServer.func1

pkg/server/mcp.go

This anonymous function within `RunMCPServer` handles scan requests for the MCP (Mark3 C&C Protocol) server. Similar to the REST API's `postScanHandler`, it was vulnerable because it accepted scan options from a remote source without sanitizing fields that could control filesystem operations. This provided a second entry point for the same arbitrary file write vulnerability.

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Miggo AI

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WAF Rule

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Reasoning

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