CVE-2024-32877

During the internal penetration testing of our product based on Yii2, we discovered an XSS vulnerability within the framework itself. This issue is relevant for the latest version of Yii2 (2.0.49.3).

Conditions for vulnerability reproduction

• The framework is in debug mode (YII_DEBUG set to true).
• The php.ini setting zend.exception_ignore_args is set to Off (default value).
• An attacker induces an exception in the application, leading to a stack trace page being displayed.

Vulnerability description

The issue lies in the mechanism for displaying function argument values in the stack trace. The vulnerability manifests when an argument's value exceeds 32 characters. For convenience, argument values exceeding this limit are truncated and displayed with an added "...". The full argument value becomes visible when hovering over it with the mouse, as it is displayed in the title attribute of a span tag. However, the use of a double quote (") allows an attacker to break out of the title attribute's value context and inject their own attributes into the span tag, including malicious JavaScript code through event handlers such as onmousemove.

Demonstration example:
http://31.184.254.143/about/aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa%22%20onmousemove=alert(1)%20style=%22width:%20100000px;%20height:%20100000px;%20position:%20absolute;%20top:%20-10000px;%20left:%200;%22

Impact of the vulnerability

This vulnerability allows an attacker to execute arbitrary JavaScript code in the security context of the victim's site via a specially crafted link. This could lead to the theft of cookies (including httpOnly cookies, which are accessible on the page), content substitution, or complete takeover of user accounts.

Technical analysis and mitigation suggestion

Upon analyzing the framework's source code, it was found that data handling for the title attribute is performed in the file framework/web/ErrorHandler.php. The identified problem is related to changes made in the commit https://github.com/yiisoft/yii2/commit/8cc9aeb2f0b2ffe02fb54a817064e9da75512706 , which led to the disabling of encoding for single and double quotes in the htmlEncode method (https://github.com/yiisoft/yii2/blob/8cc9aeb2f0b2ffe02fb54a817064e9da75512706/framework/web/ErrorHandler.php#L183) due to the addition of the ENT_NOQUOTES flag. To address this issue while preserving the functionality intended by the commit, we suggest modifying the htmlEncode method as follows:

    return htmlspecialchars($text, ENT_QUOTES | ENT_SUBSTITUTE | ENT_HTML5, 'UTF-8');

This change will effectively prevent the XSS vulnerability while maintaining the targeted functionality of the previous changes.

Conclusion

Based on the above, we strongly recommend implementing the suggested changes to the project's main code as soon as possible to protect framework users from potential attacks. I am ready to provide further information or assistance, including creating a pull request if necessary.

Untrusted input is rendered as active markup in a victim's browser, which can run script in their session. Typical impact: session or credential theft, and actions taken as the user.

CVE-2024-32877 has a CVSS score of 4.2 (Medium). The vector is network-reachable, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.0.49.4); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2024-32877? CVE-2024-32877 is a medium-severity cross-site scripting (XSS) vulnerability in yiisoft/yii2 (composer), affecting versions >= 2.0.43, < 2.0.49.4. It is fixed in 2.0.49.4. Untrusted input is rendered as active markup in a victim's browser, which can run script in their session.
2. How severe is CVE-2024-32877? CVE-2024-32877 has a CVSS score of 4.2 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of yiisoft/yii2 are affected by CVE-2024-32877? yiisoft/yii2 (composer) versions >= 2.0.43, < 2.0.49.4 is affected.
4. Is there a fix for CVE-2024-32877? Yes. CVE-2024-32877 is fixed in 2.0.49.4. Upgrade to this version or later.
5. Is CVE-2024-32877 exploitable, and should I be worried? Whether CVE-2024-32877 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2024-32877 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2024-32877? Upgrade yiisoft/yii2 to 2.0.49.4 or later.