CVE-2025-24895: CIE.AspNetCore Auth Bypass Vulnerability

CVE-2025-24895 Overview

CVE-2025-24895 is an authentication bypass vulnerability in CIE.AspNetCore.Authentication, an AspNetCore Remote Authenticator for CIE 3.0 (Carta d'Identità Elettronica - Italian Electronic Identity Card). The vulnerability exists in the SAML2 assertion validation logic used by Service Providers (SP) when processing identity information from Identity Providers (IDP).

The flaw stems from improper signature verification ordering in SAML responses. The library fails to guarantee that the first signature refers to the root object, allowing an attacker to inject a legitimately signed XML element as the first element. When this occurs, all subsequent signatures in the SAML response are not verified, effectively bypassing the authentication mechanism.

Critical Impact

An attacker can craft arbitrary SAML responses that are accepted by Service Providers using vulnerable SDKs, enabling complete impersonation of any Spid and/or CIE user without valid credentials.

Affected Products

• CIE.AspNetCore.Authentication versions prior to 2.1.0
• Applications implementing SAML2 authentication using the vulnerable cie-aspnetcore library
• Service Providers relying on Spid and CIE identity federation

Discovery Timeline

• 2025-02-18 - CVE CVE-2025-24895 published to NVD
• 2025-02-18 - Last updated in NVD database

Technical Details for CVE-2025-24895

Vulnerability Analysis

This vulnerability represents a fundamental flaw in how the CIE.AspNetCore.Authentication library validates SAML assertions. The SAML2 standard relies on XML digital signatures to ensure the integrity and authenticity of identity assertions passed between Identity Providers and Service Providers. When a user authenticates via an IDP, the resulting SAML response contains signed assertions that the SP must validate before granting access.

The vulnerable library processes signatures in sequence but assumes the first signature encountered corresponds to the root SAML response element. This assumption creates a critical security gap that attackers can exploit by prepending a legitimately signed but unrelated XML element to a crafted SAML response. Because the library verifies only the first signature and skips validation of subsequent signatures, the malicious assertions embedded in the response are accepted as authentic.

The attack is particularly dangerous because Identity Providers publish their public metadata, which includes legitimately signed XML elements. An attacker can extract these signed elements and use them to construct fraudulent SAML responses that pass the vulnerable validation logic.

Root Cause

The root cause is classified under CWE-287 (Improper Authentication). The signature verification implementation fails to properly bind signature validation to the specific XML elements they are meant to protect. Instead of ensuring cryptographic verification of the actual SAML assertion content, the library relies on positional ordering of signatures within the XML document, creating a signature wrapping vulnerability.

Attack Vector

The attack is network-accessible and requires no authentication or user interaction. An attacker can exploit this vulnerability by:

1. Obtaining legitimately signed XML elements from the publicly available IdP metadata
2. Constructing a malicious SAML response with arbitrary identity claims
3. Prepending the legitimately signed element to the malicious response
4. Submitting the crafted SAML response to a vulnerable Service Provider
5. The SP validates only the first (legitimate) signature and accepts the entire response
6. The attacker gains authenticated access as any Spid or CIE user

The vulnerability manifests in the SAML response signature validation logic where the library iterates through signature elements without properly validating their reference targets. When an attacker injects a legitimately signed XML element at the beginning of the SAML response, the validation process verifies this first signature successfully and bypasses verification of the actual assertion signatures. For detailed technical analysis, see the GitHub Security Advisory.

Detection Methods for CVE-2025-24895

Indicators of Compromise

• Anomalous SAML responses containing multiple signature elements with unexpected ordering
• Authentication events where the authenticated user identity does not match expected patterns
• SAML responses with XML elements that reference external or public metadata signatures
• Unusual authentication success from IP addresses or locations inconsistent with legitimate user behavior

Detection Strategies

• Implement deep packet inspection for SAML traffic to identify responses with suspicious signature element ordering
• Monitor authentication logs for users authenticating from unusual geographic locations or devices
• Deploy application-layer security monitoring to analyze SAML assertion content before processing
• Establish baseline authentication patterns and alert on deviations indicating potential impersonation attacks

Monitoring Recommendations

• Enable detailed logging of all SAML authentication transactions including full assertion content
• Configure alerts for authentication events involving high-privilege accounts or sensitive resources
• Implement real-time correlation of authentication events with user behavioral analytics
• Monitor for bulk authentication attempts that could indicate automated exploitation

How to Mitigate CVE-2025-24895

Immediate Actions Required

• Upgrade CIE.AspNetCore.Authentication to version 2.1.0 or later immediately
• Audit authentication logs for any suspicious Spid or CIE authentication events prior to patching
• Review all Service Provider applications using the cie-aspnetcore library for exposure
• Consider temporarily disabling affected authentication endpoints if patching is delayed

Patch Information

The vulnerability has been addressed in CIE.AspNetCore.Authentication version 2.1.0. All users are strongly advised to upgrade immediately. The fix ensures proper signature validation by verifying that signatures correctly reference and protect the intended XML elements in SAML responses, preventing signature wrapping attacks.

Update to the patched version via NuGet:

dotnet add package CIE.AspNetCore.Authentication --version 2.1.0

For additional details, refer to the GitHub Security Advisory.

Workarounds

• No workarounds are available for this vulnerability according to the security advisory
• Upgrading to version 2.1.0 is the only effective remediation
• Consider implementing additional authentication factors as a defense-in-depth measure while planning the upgrade
• Network-level restrictions on SAML endpoints may reduce exposure but do not fully mitigate the risk

# Configuration example - Upgrade to patched version
# Update your project's package reference
dotnet add package CIE.AspNetCore.Authentication --version 2.1.0

# Verify installed version
dotnet list package | grep CIE.AspNetCore.Authentication