CVE-2025-1861 - PHP Vulnerability in HTTP Redirect Parsing Due to Limited Location Buffer

This blog post discusses a vulnerability discovered in various PHP versions, specifically 8.1.*, 8.2.*, 8.3.*, and 8.4.*. The issue is due to the limited size of the location buffer when parsing HTTP redirects, which could potentially cause URL truncation and redirection to incorrect locations. In this article, we will discuss the details of the vulnerability, provide a code snippet to illustrate the problem, and provide links to the original references.

Vulnerability Details

The vulnerability (CVE-2025-1861) is observed in PHP versions from 8.1.* before 8.1.32, from 8.2.* before 8.2.28, from 8.3.* before 8.3.19, and from 8.4.* before 8.4.5. As mentioned earlier, this issue is related to the parsing of HTTP redirects when processing an HTTP response.

In these affected PHP versions, there is a limit on the location value size due to the location buffer being restricted to 1024 bytes. However, as per RFC911 (https://www.rfc-editor.org/info/rfc911), the recommended limit for location value size should be 800 bytes. This mismatch in the location buffer limit could potentially result in incorrect URL truncation and, subsequently, causing users to be redirected to the wrong location.

Code Snippet

<?php
$url = 'https://example.com/redirect?url='; . str_repeat('A', 900);

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_FOLLOWLOCATION, 1);
curl_exec($ch);
curl_close($ch);
?>

In this example, the PHP code initiates a cURL request to a URL that includes a long redirect value. Due to the limited location buffer size in the affected PHP versions, the actual URL might get truncated incorrectly, causing users to be redirected to a potentially unintended location.

Exploit Details

The risk and impact of this vulnerability depend on the specific implementation and usage scenario. A threat actor could potentially exploit this vulnerability by crafting a malicious URL, causing an unsuspecting user to be redirected to a potentially harmful website, which could potentially be utilized for phishing or other malicious activities.

Mitigation and Conclusion

To prevent this vulnerability, it is crucial to ensure that your PHP environment is patched to the latest version, which includes a fix for CVE-2025-1861. Specifically, make sure to update PHP to version 8.1.32 or later, 8.2.28 or later, 8.3.19 or later, and 8.4.5 or later.

In conclusion, always keep your PHP environment updated to the latest versions, and be cautious when dealing with HTTP redirects in your web applications. Regularly review and audit your codebase for potential vulnerabilities and apply patches as needed to minimize the risk of exploitation.

Timeline

Published on: 03/30/2025 06:15:14 UTC
Last modified on: 04/01/2025 20:26:30 UTC

Vulnerability Details

Code Snippet

Exploit Details

Mitigation and Conclusion

Further Reading and References

Timeline