Executive Summary

CVE-2026-40039 is an open redirection vulnerability in Pachno version 1.0.6 caused by improper validation of the "return_to" parameter.

Attackers can manipulate this parameter to craft malicious login URLs that redirect users to arbitrary external websites.

This flaw enables attackers to conduct phishing attacks by redirecting users to malicious sites designed to steal user credentials.

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Impact Analysis

This vulnerability can impact you by allowing attackers to redirect users to malicious external websites through manipulated login URLs.

Such redirections can be used to conduct phishing attacks aimed at stealing user credentials, potentially compromising user accounts and sensitive information.

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Detection Guidance

This vulnerability can be detected by monitoring for HTTP requests that include the "return_to" parameter with external or suspicious URLs. Analyzing web server logs for login URLs containing manipulated "return_to" values can help identify potential exploitation attempts.

You can use commands to search web server logs for such patterns. For example, using grep on Apache or Nginx logs:

• grep -i 'return_to=http' /var/log/apache2/access.log
• grep -i 'return_to=http' /var/log/nginx/access.log

Additionally, monitoring for unusual redirects or phishing attempts involving the "return_to" parameter in URLs can help detect exploitation.

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Mitigation Strategies

Immediate mitigation steps include validating and sanitizing the "return_to" parameter to ensure it only allows internal URLs or trusted domains.

If possible, disable or restrict the use of the "return_to" parameter until a patch or update is applied.

Educate users about phishing risks related to suspicious login URLs and encourage them to verify URLs before entering credentials.

Monitor web server logs for suspicious activity involving the "return_to" parameter and block or filter malicious requests.

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Compliance Impact

The vulnerability allows attackers to redirect users to arbitrary external websites via a manipulated return_to parameter, facilitating phishing attacks and potential credential theft.

Such phishing attacks and credential theft can lead to unauthorized access to personal or sensitive data, which may result in non-compliance with data protection regulations like GDPR and HIPAA that require safeguarding user data and preventing unauthorized access.

Therefore, this vulnerability poses a risk to compliance with common standards and regulations by potentially enabling data breaches through social engineering attacks.

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