CVE-2020-5421: Spring Framework Auth Bypass Vulnerability

CVE-2020-5421 Overview

CVE-2020-5421 is a security vulnerability in VMware Spring Framework that allows attackers to bypass Reflected File Download (RFD) attack protections that were originally implemented in response to CVE-2015-5211. The bypass is achieved through the use of a jsessionid path parameter, and the success of exploitation depends on the browser being used by the victim.

Reflected File Download attacks are a class of web application vulnerabilities that can trick users into downloading and executing malicious files. The original protections implemented in Spring Framework were designed to prevent attackers from manipulating HTTP response headers to create downloadable content with attacker-controlled filenames. This vulnerability represents a bypass of those protections, potentially allowing attackers to resume RFD attack techniques against Spring Framework applications.

Critical Impact

Attackers can bypass RFD attack protections to potentially trick users into downloading malicious files, leading to client-side code execution and compromised user systems.

Affected Products

• VMware Spring Framework versions 5.2.0 - 5.2.8
• VMware Spring Framework versions 5.1.0 - 5.1.17
• VMware Spring Framework versions 5.0.0 - 5.0.18
• VMware Spring Framework versions 4.3.0 - 4.3.28
• Oracle WebLogic Server (versions 10.3.6.0.0, 12.1.3.0.0, 12.2.1.3.0, 12.2.1.4.0, 14.1.1.0.0)
• Oracle Fusion Middleware (versions 12.2.1.3.0, 12.2.1.4.0)
• NetApp OnCommand Insight, Snap Creator Framework, and SnapCenter

Discovery Timeline

• September 19, 2020 - CVE-2020-5421 published to NVD
• November 21, 2024 - Last updated in NVD database

Technical Details for CVE-2020-5421

Vulnerability Analysis

This vulnerability exists in the Spring Framework's request handling mechanism, specifically in how it processes URL paths containing session identifiers. Spring Framework implemented protections against Reflected File Download attacks following CVE-2015-5211, which aimed to prevent attackers from manipulating response content disposition headers.

The bypass leverages the jsessionid path parameter, which is a URL rewriting technique used to maintain session state when cookies are disabled. When a request contains a jsessionid path parameter in a specific format, the RFD protection logic fails to properly sanitize or validate the request, allowing the original attack vector to be exploited.

The effectiveness of this bypass is browser-dependent, meaning certain browsers may be more susceptible to the attack than others based on how they handle content disposition headers and file downloads.

Root Cause

The root cause of this vulnerability is incomplete input validation in the RFD protection mechanism. When the original CVE-2015-5211 fix was implemented, it did not account for all possible URL encoding schemes and path parameter variations. The jsessionid path parameter represents a legitimate URL rewriting feature, but its presence in certain positions can cause the security validation logic to be bypassed.

The underlying issue stems from the complexity of URL parsing and the multiple ways session identifiers can be embedded in request paths. The protection logic failed to normalize URLs before applying security checks, allowing the jsessionid parameter to act as an escape mechanism.

Attack Vector

The attack requires network access and user interaction to be successful. An attacker would need to craft a malicious URL targeting a vulnerable Spring Framework application and convince a victim to click on it. The attack flow typically involves:

1. The attacker identifies a Spring Framework endpoint that returns user-controllable content
2. A specially crafted URL is created that includes a jsessionid path parameter designed to bypass RFD protections
3. The victim is tricked into clicking the malicious link (via phishing, social engineering, etc.)
4. The victim's browser downloads a file with an attacker-controlled filename
5. If the victim executes the downloaded file, arbitrary code may run on their system

The attack requires low privileges on the target application but does require user interaction, as the victim must click the malicious link and potentially execute the downloaded file.

Detection Methods for CVE-2020-5421

Indicators of Compromise

• Unusual URL patterns in web server logs containing jsessionid path parameters with suspicious file extensions
• HTTP requests attempting to manipulate Content-Disposition headers
• Access logs showing requests with encoded special characters in the jsessionid parameter value
• User reports of unexpected file downloads when accessing application URLs

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block requests containing suspicious jsessionid path parameter patterns
• Monitor HTTP response headers for unexpected Content-Disposition values, particularly those containing executable file extensions
• Deploy log analysis to identify URL patterns that match known RFD attack signatures
• Utilize endpoint detection solutions to identify unusual file downloads originating from web applications

Monitoring Recommendations

• Enable detailed access logging on all Spring Framework applications to capture full request URLs including path parameters
• Configure SIEM alerts for requests containing jsessionid parameters combined with file download responses
• Monitor for bulk scanning activity that may indicate attackers probing for vulnerable endpoints
• Track Content-Disposition header modifications in application responses

How to Mitigate CVE-2020-5421

Immediate Actions Required

• Upgrade VMware Spring Framework to patched versions: 5.2.9 or later, 5.1.18 or later, 5.0.19 or later
• Apply relevant patches from Oracle Critical Patch Updates for affected Oracle products
• Review application configurations to identify endpoints that may be vulnerable to RFD attacks
• Implement additional input validation at the application layer as a defense-in-depth measure

Patch Information

VMware has released patched versions of Spring Framework that address this vulnerability. Organizations should upgrade to the following minimum versions:

• Spring Framework 5.2.x: Upgrade to 5.2.9 or later
• Spring Framework 5.1.x: Upgrade to 5.1.18 or later
• Spring Framework 5.0.x: Upgrade to 5.0.19 or later
• Spring Framework 4.3.x: Upgrade to 4.3.29 or later

For Oracle products, refer to the Oracle CPU April 2021 Advisory, Oracle CPU January 2021 Advisory, and subsequent Critical Patch Updates. For NetApp products, refer to the NetApp Security Advisory NTAP-20210513-0009.

Additional vendor advisories are available from VMware Security Advisory.

Workarounds

• Disable URL session tracking by enforcing cookie-based session management only, preventing jsessionid path parameters from being processed
• Implement strict Content-Security-Policy headers to restrict file downloads and script execution
• Deploy web application firewall rules to block requests containing suspicious path parameter patterns
• Configure response header filtering to prevent manipulation of Content-Disposition headers

# Example: Disable URL-based session tracking in Spring Boot application.properties
server.servlet.session.tracking-modes=cookie

# Example: Configure Spring Security to enforce cookie-only sessions
# Add to security configuration class
# http.sessionManagement().sessionFixation().migrateSession()