SAML is not automatically insecure, but it places a substantial validation burden on the identity provider and the service that consumes its assertions. A valid signature alone is not enough: the service must trust the right key, validate the relevant conditions, and use the exact signed assertion it checked. OIDC can be a good alternative when an organization’s applications and identity ecosystem support it, but it is not a universal drop-in replacement or a guarantee of better security.
What SAML does—and where its complexity comes from
The Security Assertion Markup Language (SAML) is an XML-based framework for exchanging authentication, entitlement, and attribute information. In browser-based single sign-on, an identity provider (IdP) sends an assertion to a service provider (SP), which validates it and may use it to establish a session or assign user attributes. OWASP describes SAML as “an open standard for exchanging authorization and authentication information” in its SAML Security Cheat Sheet.
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The security outcome depends on the selected profile and binding, how the parties establish trust, and how the SP validates and consumes the message. XML signatures and document structure make it possible for validation and application code to disagree about which element was signed. Metadata and signing-key trust also need careful handling. The central challenge is therefore not simply that SAML uses XML; it is that a relying service must correctly connect trusted keys, signed content, protocol conditions, and the exact data used to authenticate a user.
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Why a valid signature is not enough
A signature shows that particular content was signed with a key. It does not, by itself, establish that the key belongs to the expected IdP, that the message is intended for this SP, that it is timely, or that the application is using the same signed assertion it validated. The SP must make those checks together.
- Trust the signer: validate against a signing key obtained through a trusted configuration or metadata process. Do not let an untrusted
KeyInfoelement supply the basis for deciding which key to trust. - Bind validation to use: safely select the security-sensitive XML nodes and ensure the exact Response or Assertion consumed by the application is the one whose signature passed validation.
- Check protocol context: confirm the issuer, audience, recipient, request correlation, subject confirmation, and time conditions against the expected values for the transaction.
- Validate structure and algorithms: validate XML against trusted local schemas and reject weak signature or digest algorithms.
These are implementation-sensitive controls, not optional polish. OWASP’s SAML security guidance details these checks.
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What documented SAML vulnerabilities show
Public vulnerability records show that signature-handling mistakes can have serious consequences. They concern specific products and version ranges; they do not establish how common such flaws are across all SAML deployments. The NVD records below describe distinct implementation failures.
| Record | Affected software and flaw | Fix information in the record |
|---|---|---|
| CVE-2024-6800 | NVD describes an XML signature-wrapping flaw in GitHub Enterprise Server’s SAML use with specific identity providers using publicly exposed signed federation metadata. An attacker with direct network access could forge a response and provision or gain site-administrator access without prior authentication. | NVD lists fixes in GHES 3.13.3, 3.12.8, 3.11.14, and 3.10.16; earlier versions are affected as described in the record. |
| CVE-2024-45409 | NVD says specified Ruby-SAML releases did not properly verify the SAML Response signature. An attacker possessing an IdP-signed SAML document could forge a response or assertion with arbitrary contents and log in as an arbitrary user. | NVD lists fixes in Ruby-SAML 1.17.0 and 1.12.3. |
| CVE-2022-39299 | NVD records an authentication bypass associated with signature verification in Passport-SAML / node-saml. | NVD says to upgrade Passport-SAML to 3.2.2 or newer and identifies affected beta node-saml releases before 4.0.0-beta.5. |
These incidents demonstrate the impact of getting validation wrong and the importance of tracking and applying security updates. They do not provide a population-wide estimate of the share of SAML deployments that are vulnerable. Check the current vendor and NVD advisories for the software and versions actually in use.
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How to harden a SAML deployment
Organizations that retain SAML should review the full assertion-handling path, from trusted metadata and key configuration through the application’s session decision. OWASP recommends the following controls:
- Validate XML against trusted local schemas before making security decisions; do not fetch schemas automatically from third-party locations.
- Use trusted IdP signing keys. Do not accept an untrusted
KeyInfovalue as the authority for signature validation. - Select XML nodes safely and verify that the precise signed Response or Assertion used to authenticate the user is the one that passed validation.
- Check the Audience against the SP EntityID, along with
NotBefore,NotOnOrAfter, Recipient,InResponseTo, and subject confirmation conditions. - Reject SHA-1-based signature and digest algorithms. OWASP says to require at least RSA-SHA-256 or stronger.
- Use secure transport, define logout and session-management criteria, and patch the SAML implementation and dependent libraries.
- Operate metadata and signing-key trust deliberately, including key rollover, so changes are authenticated and old trust is retired appropriately.
Encryption has its own requirements. OASIS SAML Version 2.0 Errata 05 cautions that when CBC-mode algorithms are used for encrypted SAML data, relying parties should require integrity protection before processing the content. Follow the applicable profile and standard errata; encryption alone does not establish integrity.
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Should you replace SAML with OIDC?
OIDC is a genuine alternative in suitable federation contexts. NIST SP 800-63C discusses both SAML assertions and OIDC ID Tokens as federation assertions, but that does not make OIDC an automatic replacement for every SAML integration. Neither protocol removes the need for correct trust configuration, validation, and operational maintenance.
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Compare the protocols against the requirements and systems you actually have:
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- WORKS WITH 1000+ ACCOUNTS: Compatible with Google, Microsoft, and Apple. A single Security Key C NFC secures 100 of your favorite accounts, including email, password managers, and more.
- FAST & CONVENIENT LOGIN: Plug in your Security Key C NFC via USB-C and tap it, or tap it against your phone (NFC) to authenticate. No batteries, no internet connection, and no extra fees required.
- TRUSTED PASSKEY TECHNOLOGY: Uses the latest passkey standards (FIDO2/WebAuthn & FIDO U2F) but does not support One-Time Passwords. For complex needs, check out the YubiKey 5 Series.
- Compatibility: inventory IdPs, SPs, partners, and applications, including systems that require SAML.
- Assurance and federation model: confirm that the protocol and configuration support the required assurance level and relationships.
- Application architecture: check which front-channel or back-channel flows the applications support.
- Operational capability: assess the complexity of key and metadata lifecycles and whether the team can validate the chosen protocol correctly.
- Migration risk: account for compatibility gaps, transition scope, and the possibility that a bridge or continued SAML support will be necessary.
For a new integration, prefer a modern, well-supported federation protocol that fits the environment and can be implemented with mature libraries and strict validation. Choose OIDC where the application and identity ecosystem support it; retain or bridge SAML where compatibility requires it. There is not enough evidence to claim that OIDC is always safer.
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Standards and further guidance
- NIST SP 800-63C discusses federation assertions, including SAML and OIDC.
- OASIS Security Services Technical Committee provides information on the committee responsible for SAML security services standards.
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