CVE-2026-3963: perfree go-fastdfs-web Auth Bypass Flaw

CVE-2026-3963 Overview

A security vulnerability has been discovered in perfree go-fastdfs-web up to version 1.3.7 that involves the use of a hard-coded cryptographic key in the Apache Shiro RememberMe functionality. This flaw affects the rememberMeManager function within src/main/java/com/perfree/config/ShiroConfig.java, allowing attackers to potentially exploit the predictable cryptographic key for malicious purposes.

The vulnerability can be exploited remotely over the network, though the attack complexity is considered high. The exploit has been publicly released and may be used for attacks. The vendor was contacted regarding this disclosure but did not respond.

Critical Impact

Hard-coded cryptographic keys in Apache Shiro's RememberMe feature can allow attackers to forge authentication tokens, potentially leading to remote code execution through deserialization attacks.

Affected Products

• perfree go-fastdfs-web versions up to and including 1.3.7
• Applications using the affected ShiroConfig.java configuration
• Systems with Apache Shiro RememberMe functionality enabled

Discovery Timeline

• March 11, 2026 - CVE-2026-3963 published to NVD
• March 12, 2026 - Last updated in NVD database

Technical Details for CVE-2026-3963

Vulnerability Analysis

This vulnerability stems from the use of a hard-coded cryptographic key in the Apache Shiro framework's RememberMe functionality within go-fastdfs-web. Apache Shiro uses AES encryption to secure the RememberMe cookie, and when developers use a static, hard-coded cipher key instead of generating unique keys per deployment, all installations share the same encryption secret.

When an attacker knows the cipher key, they can craft malicious serialized Java objects, encrypt them using the known key, and submit them as RememberMe cookies. The server then decrypts and deserializes these objects, potentially executing arbitrary code if vulnerable gadget chains are present in the classpath.

The network-based attack vector combined with no required privileges makes this vulnerability exploitable by unauthenticated remote attackers, though the high attack complexity indicates successful exploitation requires specific conditions or technical expertise.

Root Cause

The root cause of CVE-2026-3963 is CWE-320: Key Management Errors. Specifically, the rememberMeManager function in ShiroConfig.java configures Apache Shiro with a static, hard-coded cipher key rather than generating or retrieving a unique cryptographic key at runtime. This violates secure cryptographic practices where encryption keys should be unique per deployment, securely generated, and stored separately from application code.

Hard-coded keys are particularly dangerous because:

• They are identical across all installations of the software
• They can be extracted by examining the source code or compiled bytecode
• Once discovered, all deployments using that version become vulnerable

Attack Vector

The attack can be initiated remotely over the network without authentication. An attacker who obtains the hard-coded cipher key can:

1. Extract the hard-coded key from the application source code or decompile the Java bytecode
2. Craft a malicious Java serialized object containing a gadget chain for code execution
3. Encrypt the payload using AES with the known cipher key
4. Base64-encode the encrypted payload and set it as the rememberMe cookie value
5. Send the request to the target server, which decrypts and deserializes the malicious object

The vulnerability mechanism involves the predictable AES cipher key used in Shiro's cookie management. When the server processes incoming requests with the rememberMe cookie, it uses the hard-coded key to decrypt the cookie value and then deserializes the resulting object. If the deserialized object contains a malicious gadget chain (such as Commons Collections or other known Java deserialization exploits), arbitrary code execution occurs.

For technical details on the exploitation mechanism, see the RCE Analysis on Hardcoded Key documentation.

Detection Methods for CVE-2026-3963

Indicators of Compromise

• Unusual or overly long rememberMe cookie values in HTTP requests
• Base64-encoded payloads in cookie headers that decode to serialized Java objects
• Unexpected Java deserialization activity or class loading on the server
• Anomalous process spawning or network connections originating from the web application process

Detection Strategies

• Monitor HTTP traffic for suspicious rememberMe cookie patterns, particularly unusually large cookie values
• Implement Java deserialization monitoring to detect attempts to instantiate known dangerous classes
• Deploy web application firewalls (WAF) with rules to detect serialized Java object patterns in cookies
• Review application logs for Shiro-related exceptions or authentication anomalies

Monitoring Recommendations

• Enable verbose logging for Apache Shiro authentication and session management
• Set up alerts for failed deserialization attempts or unexpected class instantiation
• Monitor for reconnaissance activity targeting Shiro endpoints or attempting to enumerate application versions
• Implement runtime application self-protection (RASP) to detect deserialization attacks

How to Mitigate CVE-2026-3963

Immediate Actions Required

• Upgrade go-fastdfs-web beyond version 1.3.7 if a patched version becomes available
• Generate a unique, cryptographically secure cipher key and configure Shiro to use it instead of the hard-coded value
• Consider disabling the RememberMe functionality if not essential to application operation
• Review and restrict the Java classpath to remove unnecessary libraries that may contain deserialization gadget chains

Patch Information

No official vendor patch information is currently available. The vendor was contacted about this vulnerability but did not respond. Organizations should implement the workarounds below and monitor for vendor updates.

For additional technical details and threat intelligence, see the VulDB advisory.

Workarounds

• Replace the hard-coded cipher key with a securely generated random key stored in external configuration
• Disable Apache Shiro's RememberMe feature by removing or commenting out the rememberMeManager configuration
• Implement a Java agent or security manager to block dangerous deserialization classes
• Deploy network-level controls to inspect and sanitize incoming cookie values

# Generate a secure random Base64-encoded key for Shiro cipher
# Replace the hard-coded key in ShiroConfig.java with this value
openssl rand -base64 16

# Example: Store the generated key in application.properties
# shiro.rememberMe.cipherKey=YOUR_GENERATED_KEY_HERE

# If disabling RememberMe entirely, ensure the configuration removes:
# cookieRememberMeManager and rememberMeManager bean definitions