CVE-2022-31158 is an authentication bypass vulnerability identified in the packbackbooks lti-1-3-php-library, a PHP library used to build IMS-certified LTI 1.3 tool providers. The vulnerability arises from improper validation of the Nonce Claim Value in versions prior to 5.0. Specifically, the library fails to verify that the nonce value received in the authentication request matches the nonce claim value, enabling an attacker to perform a capture-replay attack. This means an adversary could intercept a legitimate authentication request and replay it to gain unauthorized access without proper authentication. Since the nonce is intended to prevent replay attacks by ensuring each authentication request is unique and used only once, this flaw undermines the integrity of the authentication mechanism. The vulnerability is categorized under CWE-294 (Authentication Bypass by Capture-replay). There are no known workarounds, and the only remediation is upgrading to version 5.0 or later, where nonce validation has been properly implemented. No exploits have been reported in the wild to date, but the vulnerability poses a risk to any system relying on this library for LTI 1.3 tool integration, particularly in educational technology platforms that use LTI standards for interoperability between learning tools and platforms.

For European organizations, particularly educational institutions and edtech providers that utilize LTI 1.3 integrations built with the vulnerable packbackbooks PHP library, this vulnerability could allow unauthorized access to learning tools and platforms. An attacker exploiting this flaw could impersonate legitimate users or services, potentially accessing sensitive educational data, modifying course content, or disrupting learning activities. The impact extends to confidentiality (unauthorized data access), integrity (unauthorized modification of content or user data), and availability (potential disruption of services through replay attacks). Given the widespread adoption of LTI standards in European higher education and e-learning environments, exploitation could undermine trust in digital learning ecosystems and lead to compliance issues with data protection regulations such as GDPR if personal data is exposed. Although no active exploits are known, the ease of replaying captured authentication requests without needing user interaction or credentials increases the risk if attackers gain access to network traffic or logs containing nonce values.

The primary and most effective mitigation is to upgrade the packbackbooks lti-1-3-php-library to version 5.0 or later, where nonce validation is correctly enforced. Organizations should audit their software dependencies to identify usage of vulnerable versions and prioritize patching. Additionally, network-level protections such as enforcing TLS encryption for all LTI authentication traffic can reduce the risk of nonce capture. Implementing strict monitoring and logging of authentication requests to detect replay patterns can help identify attempted exploits. Where possible, deploying web application firewalls (WAFs) with custom rules to detect and block replayed authentication requests may provide an additional layer of defense. Organizations should also review their LTI integration configurations to ensure adherence to best practices, including short nonce lifetimes and nonce uniqueness enforcement. Finally, educating developers and administrators about the importance of nonce validation in authentication flows can prevent similar issues in custom or third-party integrations.