CVE-2025-45769: Firebase Php-jwt Information Disclosure

CVE-2025-45769 Overview

CVE-2025-45769 affects Google Firebase php-jwt version 6.11.0, a widely deployed PHP library for creating and validating JSON Web Tokens (JWT). The advisory reports weak encryption behavior related to how the library handles cryptographic key material. The issue is categorized under [CWE-326: Inadequate Encryption Strength].

The CVE Record carries a dispute. The maintainers argue that key length selection is the responsibility of the calling application, not the library itself. The dispute is under review per CNA rules 4.1.4 and 4.1.14. Applications that pass short or low-entropy keys to php-jwt remain exposed regardless of the outcome.

Critical Impact
Weak key handling in php-jwt v6.11.0 can allow attackers to brute-force JWT signing secrets, forge tokens, and impersonate authenticated users over the network.

Affected Products

Google Firebase php-jwt v6.11.0
Applications embedding vulnerable versions of firebase/php-jwt as a Composer dependency
Downstream frameworks and SDKs that rely on php-jwt for token signing and validation

Discovery Timeline

2025-07-31 - CVE-2025-45769 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-45769

Vulnerability Analysis

The vulnerability concerns weak encryption strength in php-jwt v6.11.0. JSON Web Tokens signed with HMAC algorithms such as HS256, HS384, or HS512 rely on the entropy of the shared secret. If the library accepts secrets that are shorter than the algorithm's output length, an attacker can perform offline brute-force or dictionary attacks against captured tokens.

Once a secret is recovered, the attacker can forge arbitrary JWTs. Forged tokens allow session impersonation, privilege escalation within the application, and bypass of authorization checks. The attack occurs over the network and does not require prior authentication or user interaction.

The maintainer dispute focuses on responsibility. Guidance from RFC 7518 requires HMAC keys to be at least as long as the hash output, but the library did not enforce this constraint in v6.11.0. Applications that generate short secrets, reuse passwords, or pull keys from low-entropy sources inherit the weakness.

Root Cause

The root cause is inadequate validation of key strength before signing or verifying tokens. The library did not reject keys that fell below the minimum length recommended for the selected HMAC algorithm. See the GitHub PHP-JWT Issue Tracker and GitHub PHP-JWT Pull Request for the technical discussion.

Attack Vector

An attacker captures a signed JWT emitted by the target application. The attacker then runs an offline brute-force attack against the HMAC signature using common password lists or exhaustive search across short key spaces. Once the secret is recovered, the attacker mints new tokens with arbitrary claims and submits them to the application to gain unauthorized access.

Refer to the GitHub Security Advisory and the GitHub Gist Code Snippet for demonstration material.

Detection Methods for CVE-2025-45769

Indicators of Compromise

Unexpected successful authentications using JWTs whose iat or exp claims fall outside normal issuance patterns
Repeated JWT verification failures followed by a successful verification from the same client IP, suggesting key-guessing attempts
JWT payloads containing elevated roles, administrative claims, or user identifiers that were not issued by the application's token service

Detection Strategies

Inventory Composer dependencies across PHP applications and flag any project pinning firebase/php-jwt at v6.11.0 or earlier
Audit application configuration to identify HMAC signing secrets shorter than 32 bytes for HS256, 48 bytes for HS384, or 64 bytes for HS512
Enable verbose logging on token verification failures and correlate failures with subsequent successful requests from the same source

Monitoring Recommendations

Forward web application and authentication logs to a centralized analytics platform for correlation of JWT verification anomalies
Alert on privileged actions performed by sessions whose JWTs were minted outside the identity provider's issuance window
Track dependency updates in CI/CD pipelines and block builds that reintroduce vulnerable php-jwt versions

How to Mitigate CVE-2025-45769

Immediate Actions Required

Upgrade firebase/php-jwt to v7.0.0 or later, which addresses the key strength concerns raised in the advisory
Rotate all HMAC signing secrets and invalidate outstanding tokens after the upgrade
Replace any secrets shorter than the HMAC algorithm output length with cryptographically random values of adequate size

Patch Information

The fixed release is available at GitHub PHP-JWT Release v7.0.0. Review the GitHub Advisory Database Pull Request for the coordinated advisory metadata. Update dependencies via Composer and redeploy affected services.

Workarounds

Enforce a minimum key length in application code before invoking JWT::encode() or JWT::decode(), rejecting secrets below the algorithm's hash output size
Migrate from symmetric HMAC signing to asymmetric algorithms such as RS256 or ES256, which rely on private keys rather than shared secrets
Generate secrets using random_bytes(64) and store them in a secrets manager rather than configuration files or environment variables committed to source control

bash

# Configuration example
composer require firebase/php-jwt:^7.0
php -r "echo bin2hex(random_bytes(64));" > /etc/app/jwt.secret
chmod 600 /etc/app/jwt.secret