CVE-2020-1957: Apache Shiro Auth Bypass Vulnerability

CVE-2020-1957 Overview

CVE-2020-1957 is a critical authentication bypass vulnerability affecting Apache Shiro before version 1.5.2. When Apache Shiro is used in conjunction with Spring dynamic controllers, a specially crafted HTTP request can bypass authentication mechanisms entirely. This vulnerability allows unauthenticated attackers to access protected resources and perform unauthorized actions within affected applications.

Critical Impact

Unauthenticated remote attackers can bypass authentication controls to access protected resources in applications using Apache Shiro with Spring dynamic controllers, potentially leading to complete system compromise.

Affected Products

• Apache Shiro versions prior to 1.5.2
• Debian Linux 8.0
• Applications using Apache Shiro with Spring dynamic controllers

Discovery Timeline

• 2020-03-25 - CVE-2020-1957 published to NVD
• 2024-11-21 - Last updated in NVD database

Technical Details for CVE-2020-1957

Vulnerability Analysis

This authentication bypass vulnerability occurs due to improper handling of request paths when Apache Shiro is integrated with Spring's dynamic controller routing mechanism. The root cause lies in a path normalization discrepancy between how Shiro processes URL patterns for security filtering and how Spring resolves controller endpoints. When an attacker crafts a request with specific path manipulations, Shiro's security filter may evaluate the path differently than Spring's dispatcher, allowing the request to bypass authentication checks while still being routed to protected controller methods.

The vulnerability is particularly dangerous because it requires no authentication or special privileges to exploit. An attacker can send requests directly over the network without any user interaction required. Successful exploitation grants unauthorized access to protected application functionality, potentially exposing sensitive data, enabling unauthorized modifications, or allowing further system compromise.

Root Cause

The vulnerability stems from inconsistent URL path handling between Apache Shiro's security filter chain and Spring Framework's request dispatcher. Shiro uses its own path matching algorithm to determine which security filters apply to incoming requests, while Spring uses a different mechanism to map requests to controller methods. When certain specially crafted path patterns are submitted, these two systems interpret the path differently. Shiro's filter may determine that no authentication is required for the normalized path, while Spring still routes the original request to a protected endpoint. This semantic gap creates an authentication bypass condition.

Attack Vector

The attack vector is network-based, requiring no authentication and no user interaction. An attacker constructs HTTP requests with manipulated URL paths designed to exploit the path handling discrepancy between Shiro and Spring. The attack involves sending requests where the path satisfies Shiro's security bypass conditions while still resolving to protected Spring controller endpoints.

Typical exploitation patterns include:

1. Path manipulation using special characters or encoding
2. Requests that exploit differences in how trailing slashes, semicolons, or URL-encoded characters are processed
3. Crafted requests that trigger Spring's Ant-style path matching differently than Shiro's pattern matching

The vulnerability affects any application that uses Apache Shiro for authentication/authorization in combination with Spring's dynamic controller routing. Exploitation allows complete bypass of Shiro's security framework, granting access to any protected resources.

Detection Methods for CVE-2020-1957

Indicators of Compromise

• Unusual access patterns to protected endpoints without valid authentication sessions
• HTTP requests containing suspicious path patterns with semicolons, double slashes, or URL-encoded characters targeting protected resources
• Authentication logs showing access to restricted resources without corresponding login events
• Anomalous requests to Spring MVC endpoints that bypass expected Shiro filter chains

Detection Strategies

• Monitor web application logs for requests to protected endpoints lacking authentication tokens or session identifiers
• Implement web application firewall (WAF) rules to detect path manipulation attempts including semicolon injection and URL encoding anomalies
• Deploy runtime application self-protection (RASP) to detect authentication bypass attempts at the application layer
• Review access logs for discrepancies between Shiro filter chain processing and actual endpoint access

Monitoring Recommendations

• Enable verbose logging for both Apache Shiro security filter chains and Spring MVC request routing
• Configure alerting for any access to authenticated endpoints without valid session tokens
• Implement centralized log correlation to identify patterns indicating authentication bypass attempts
• Monitor for requests with unusual path characteristics targeting sensitive application areas

How to Mitigate CVE-2020-1957

Immediate Actions Required

• Upgrade Apache Shiro to version 1.5.2 or later immediately
• Audit application access logs for signs of exploitation since the application was deployed
• Review and restrict network access to affected applications until patching is complete
• Implement additional authentication controls at the network or reverse proxy layer as a defense-in-depth measure

Patch Information

Apache has released version 1.5.2 which addresses this authentication bypass vulnerability. Organizations should upgrade to Apache Shiro 1.5.2 or the latest available version. For detailed patch information and discussion, see the Apache Shiro Dev Discussion and the Apache Shiro Commits Update.

Debian Linux users should refer to the Debian LTS Announcement for distribution-specific patching guidance.

Workarounds

• Implement strict path validation at the web server or reverse proxy level before requests reach the application
• Configure additional authentication mechanisms independent of Shiro at network perimeter devices
• Restrict access to vulnerable applications to trusted networks only until patching is completed
• Consider deploying a WAF with rules specifically targeting path manipulation techniques

# Verify Apache Shiro version in Maven-based projects
mvn dependency:tree | grep shiro

# Check current Shiro version in Gradle projects
gradle dependencies | grep shiro

# Update to patched version in pom.xml
# <dependency>
#   <groupId>org.apache.shiro</groupId>
#   <artifactId>shiro-core</artifactId>
#   <version>1.5.2</version>
# </dependency>