CVE-2025-24894: The AspNetCore Remote Authenticator for SPID Allows SAML Response Signature Verification Bypass

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.6%, percentile 48: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 48% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes SPID.AspNetCore.Authentication (NuGet) <= 3.3.0, fixed in 3.4.0. Check your lockfile, including transitive dependencies.

What it is

SPID.AspNetCore.Authentication is an AspNetCore Remote Authenticator for SPID. Authentication using Spid and CIE is based on the SAML2 standard which provides two entities: Identity Provider (IDP): the system that authenticates users and provides identity information (SAML affirmation) to the Service Provider, in essence, is responsible for the management of the credentials and identity of users; Service Provider (SP): the system that provides a service to the user and relies on the Identity Provider to authenticate the user, receives SAML assertions from the IdP to grant access to resources. The validation logic of the signature is central as it ensures that you cannot create a SAML response with arbitrary assertions and then impersonate other users. There is no guarantee that the first signature refers to the root object, it follows that if an attacker injects an item signed as the first element, all other signatures will not be verified. The only requirement is to have an XML element legitimately signed by the IdP, a condition that is easily met using the IdP's public metadata. An attacker could create an arbitrary SAML response that would be accepted by SPs using vulnerable SDKs, allowing him to impersonate any Spid and/or CIE user. This vulnerability has been addressed in version 3.4.0 and all users are advised to upgrade. There are no known workarounds for this vulnerability.

From the GitHub advisory

Description

Authentication using Spid and CIE is based on the SAML2 standard which provides for two entities:

Identity Provider (IdP): the system that authenticates users and provides identity information ( SAML assertions ) to the Service Provider, essentially, it is responsible for managing user credentials and identity; Service Provider (SP): The system that provides a service to the user and relies on the Identity Provider to authenticate the user, receives SAML assertions from the IdP to grant access to resources. The library spid-aspnetcorerefers to the second entity, i.e. the SP, and implements the validation logic of the SAML assertions present within the SAML response . The following is a summary diagram of an authentication flow via SAML:

As shown in the diagram, the IdP, after verifying the user's credentials, generates a signed SAML response, this is propagated to the SP by the user's browser and the SP, after verifying the signature, can extract the data needed to build the user's session.

The signature validation logic is central as it ensures that you cannot craft a SAML response with arbitrary assertions and thus impersonate other users.

Weakness type: CWE-287, CWE-290.

Product: SPID.AspNetCore.Authentication (NuGet) · Assigned by: GitHub_M · Published: 2025-02-18

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable no, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.61% probability of exploitation activity in the next 30 days; percentile 48.

Timeline

• 2025-02-18 — CVE record last updated
• 2025-02-18 — CVE record published by GitHub_M
• 2025-02-18 — GitHub-reviewed advisory GHSA-36h8-r92j-w9vw published (critical)

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-36h8-r92j-w9vw github.com
2. CVE.org record CVE-2025-24894 cve.org
3. NVD entry CVE-2025-24894 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

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