CVE-2025-45770: JWT Library Information Disclosure Flaw

CVE-2025-45770 Overview

CVE-2025-45770 is a weak encryption vulnerability identified in jwt v5.4.3, a popular JSON Web Token library. The vulnerability was discovered to contain weak encryption implementations that could potentially compromise the security of token-based authentication systems.

Note: This issue has been disputed by the vendor on the basis that key lengths are expected to be set by the application, not by this library. This dispute is currently subject to review under CNA rules 4.1.4, 4.1.14, and other applicable rules. The dispute tagging does not recommend an outcome for this CVE Record.

Critical Impact

Applications using jwt v5.4.3 with improperly configured key lengths may be vulnerable to cryptographic attacks that could compromise token integrity and confidentiality, potentially allowing authentication bypass or data exposure.

Affected Products

• jwt_project jwt v5.4.3
• Applications using the lcobucci/jwt library with weak key configurations
• Systems relying on JWT tokens generated with insufficient cryptographic strength

Discovery Timeline

• 2025-07-31 - CVE-2025-45770 published to NVD
• 2025-08-17 - Last updated in NVD database

Technical Details for CVE-2025-45770

Vulnerability Analysis

This vulnerability falls under CWE-326 (Inadequate Encryption Strength), which describes situations where cryptographic implementations may not provide sufficient protection against brute-force or cryptanalytic attacks. The jwt library allows applications to configure encryption parameters, and when weak key lengths are used, the resulting tokens may be susceptible to compromise.

The attack requires network access and involves high complexity due to the cryptographic nature of the exploit. Successful exploitation could result in low confidentiality and integrity impacts but potentially high availability impact to affected systems.

The disputed nature of this vulnerability centers on the responsibility boundary between the library and the application developer. The vendor maintains that key length configuration is an application-level concern and not a deficiency in the library itself.

Root Cause

The root cause relates to how the jwt library handles encryption key configuration. When applications fail to specify adequate key lengths, the library does not enforce minimum cryptographic strength requirements. This design decision places the security responsibility on the application developer rather than providing secure defaults or validation at the library level.

The classification as CWE-326 indicates that the encryption strength may be inadequate for protecting sensitive authentication tokens against determined attackers with sufficient computational resources.

Attack Vector

The attack vector is network-based, meaning attackers can attempt exploitation remotely without requiring local access to the target system. However, the attack complexity is rated as high, indicating that successful exploitation requires specific conditions to be met:

1. The target application must use jwt v5.4.3 with weak key configurations
2. The attacker must be able to intercept or obtain JWT tokens
3. Sufficient computational resources must be available to attempt cryptographic attacks against the weak encryption

A proof of concept demonstrating this vulnerability has been published. Technical details can be found in the GitHub Gist PoC published by the researcher.

Detection Methods for CVE-2025-45770

Indicators of Compromise

• Unusual authentication patterns or token validation failures in application logs
• Evidence of brute-force attempts against JWT token signatures
• Anomalous API requests with manipulated or forged JWT tokens
• Increased computational load on authentication services indicating cryptographic attacks

Detection Strategies

• Audit application code to identify usage of jwt v5.4.3 with weak key configurations
• Review JWT token generation to verify adequate key lengths are being used (minimum 256 bits for symmetric, 2048 bits for RSA)
• Implement monitoring for failed authentication attempts that may indicate token forgery
• Use software composition analysis (SCA) tools to identify vulnerable library versions in your codebase

Monitoring Recommendations

• Enable detailed logging for JWT token validation failures and authentication events
• Monitor for patterns of repeated authentication attempts with slightly modified tokens
• Set up alerts for unusual spikes in authentication failures or token validation errors
• Track library dependencies and receive notifications for security advisories related to jwt libraries

How to Mitigate CVE-2025-45770

Immediate Actions Required

• Review all applications using jwt v5.4.3 to verify strong key length configurations
• Ensure symmetric keys are at least 256 bits and asymmetric keys are at least 2048 bits
• Rotate any JWT signing keys that may have been configured with weak parameters
• Monitor vendor repositories for updates or official guidance regarding this dispute

Patch Information

As this vulnerability is currently disputed, no official patch has been released specifically addressing this CVE. The vendor maintains that key length configuration is an application responsibility. Organizations should:

• Review the official jwt library repository for any updates or security guidance
• Consult the maintainer's profile for announcements
• Follow CNA dispute resolution proceedings for official determination

Workarounds

• Configure strong encryption keys meeting or exceeding industry standards (256-bit symmetric, 2048-bit RSA minimum)
• Implement application-level validation to reject tokens signed with weak keys
• Consider using additional token validation mechanisms beyond cryptographic signature verification
• Implement token expiration policies to limit the window of opportunity for cryptographic attacks

# Configuration example - Verify key strength in your JWT implementation
# Ensure symmetric keys are at least 256 bits (32 bytes)
# For PHP applications using lcobucci/jwt:

# Check key length before using
KEY_LENGTH=$(echo -n "$JWT_SECRET" | wc -c)
if [ "$KEY_LENGTH" -lt 32 ]; then
    echo "WARNING: JWT secret key is less than 256 bits"
    echo "Generate a stronger key with: openssl rand -base64 32"
fi