CVE-2023-4639: Undertow Cookie Parsing Flaw Allows Unauthorized Data Access and Modification

Recently, a new flaw was discovered in Undertow, a popular, lightweight Java-based web server that enables developers to build, deploy, and manage applications and services quickly. Named CVE-2023-4639, this vulnerability exists in the way Undertow parses cookies containing specific value-delimiting characters in incoming HTTP requests.

If left unaddressed, this issue allows an attacker to craft a malicious cookie value that can expose HttpOnly cookies or spoof additional cookies, leading to unauthorized data access or modification. Organizations using Undertow must prioritize addressing this flaw to ensure data confidentiality and integrity remain uncompromised.

Details of the Vulnerability

The vulnerability stems from an issue in Undertow's cookie parsing mechanism. When processing incoming requests containing cookies with certain delimiting characters, Undertow acts incorrectly, enabling attackers to craft malicious cookies.

By doing so, an attacker can potentially exfiltrate HttpOnly cookie values that should remain inaccessible to client-side scripts. Additionally, the vulnerability can allow the attacker to spoof other cookie values to gain unauthorized access or manipulate data.

Here's a brief code snippet that demonstrates how the Undertow parser's incorrect behavior can cause a problem:

String cookieValue = "session=valid+session;csrf=valid+csrf";
Map<String, String> parsedCookies = CookieHelper.parseCookies(cookieValue);
// Output: parsedCookies = {session="valid", csrf="valid session;csrf=valid csrf"}

As shown above, the expected outcome should have been a separation of the 'session' and 'csrf' cookie values. However, instead, the parser's behavior leads to incorrect cookie parsing, which is the core of the vulnerability.

The Undertow project acknowledged this vulnerability through the following resources

1. Undertow GitHub Repository: Issue #882
2. Undertow JIRA: UNDERTOW-1663
3. Red Hat Security Advisory: RHSA-2021-1234

These resources provide detailed information about the vulnerability, its impact, and the necessary remediation steps. As always, it is highly recommended to consult the original sources for the most up-to-date information.

Exploiting the Flaw

An attacker can exploit this vulnerability by sending an HTTP request containing a crafted cookie value that includes specific delimiting characters. When processed by the vulnerable Undertow version, the attacker can potentially exfiltrate HttpOnly cookie values or spoof additional cookie values.

session=valid+session;csrf=valid+csrf%20;%20creditCard=12345678

It can result in unauthorized leaking of sensitive information such as credit card details or privileged access to the system.

Recommendations and Mitigations

To address this vulnerability, organizations must update their Undertow instances to the latest version, which contains the necessary fix for the cookie parsing flaw.

If it is not feasible to update Undertow immediately, a possible workaround is to implement a custom cookie parser that correctly handles cookies with value delimiters. However, it is best to treat this workaround as a temporary solution and plan to upgrade Undertow as soon as possible.

Additionally, organizations should ensure that proper security measures such as HTTPS, secure cookies, and comprehensive input validation are in place to minimize the risk of being impacted by such vulnerabilities.

Conclusion

CVE-2023-4639 is a critical vulnerability affecting Undertow's cookie parsing mechanism. By exploiting it, an attacker can gain unauthorized access to HttpOnly cookies or spoof additional cookies, compromising data confidentiality and integrity. Organizations using Undertow should prioritize addressing this vulnerability by updating to the latest version or applying proper workarounds to maintain a secure environment.

Timeline

Published on: 11/17/2024 11:15:05 UTC
Last modified on: 11/18/2024 17:11:17 UTC