CVE-2025-25293 is a vulnerability classified under CWE-400 (Uncontrolled Resource Consumption) affecting the ruby-saml toolkit, which provides Security Assertion Markup Language (SAML) single sign-on (SSO) capabilities for Ruby applications. The vulnerability stems from how ruby-saml handles compressed SAML responses using the zlib library. Specifically, ruby-saml performs a size check on the compressed message before decompression but does not validate the size after inflation. Attackers can exploit this by crafting compressed SAML assertions that appear small before decompression but expand to very large sizes once inflated. This discrepancy allows attackers to bypass size checks and cause excessive memory and CPU consumption during decompression, leading to a remote Denial of Service (DoS). The flaw affects ruby-saml versions earlier than 1.12.4 and versions from 1.13.0 up to but not including 1.18.0, with fixed versions being 1.12.4 and 1.18.0. The vulnerability requires no privileges, user interaction, or authentication, making it remotely exploitable over the network. The CVSS 4.0 vector (AV:N/AC:L/AT:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N/E:P) reflects a high impact on availability with low attack complexity and no required privileges. No known exploits are currently reported in the wild, but the potential for disruption is significant, especially for services relying on ruby-saml for SAML-based authentication. The root cause is inadequate validation of decompressed message size, a common pitfall when handling compressed data streams. This vulnerability highlights the importance of validating resource consumption after decompression to prevent DoS attacks.

For European organizations, the impact of CVE-2025-25293 can be substantial, particularly for those using ruby-saml in their SAML SSO implementations. A successful exploit can cause service outages by exhausting server resources during decompression of malicious SAML responses, leading to Denial of Service. This can disrupt user authentication flows, impacting business operations, employee productivity, and customer access to critical services. Organizations in sectors with high reliance on SAML-based SSO—such as finance, government, healthcare, and large enterprises—may face operational downtime and reputational damage. Additionally, prolonged outages could affect compliance with regulations like GDPR if personal data access is interrupted or if incident response is delayed. Since the vulnerability is remotely exploitable without authentication, attackers can launch DoS attacks from anywhere, increasing the risk surface. The absence of known exploits in the wild currently reduces immediate risk, but the high severity score and ease of exploitation warrant prompt remediation to avoid potential targeted attacks.

To mitigate CVE-2025-25293, organizations should immediately upgrade ruby-saml to version 1.12.4 or 1.18.0 or later, where the vulnerability is patched. If upgrading is not immediately feasible, implement network-level protections such as rate limiting and filtering of incoming SAML responses to detect and block unusually large or suspicious compressed payloads. Employ Web Application Firewalls (WAFs) with custom rules to monitor and restrict anomalous decompression resource usage. Additionally, review and harden SAML response validation logic to include decompressed size checks and resource usage limits. Monitor system resource metrics closely for unusual spikes during SAML processing. Conduct thorough testing of SAML integrations to ensure that decompression and size validation are robust. Finally, maintain up-to-date inventories of ruby-saml versions in use across all applications and enforce patch management policies to prevent vulnerable versions from remaining in production.