External risk intelligence

Ueberauth Apple Authentication Bypass Allows Account Takeover

CVE advisorySeverity: CRITICAL (CVSS 9.1)

CVE-2026-55954

This vulnerability affects an authentication strategy used in web applications to handle identity provider callbacks. Since it involves processing external identity tokens for user authentication, the vulnerable component is exposed as part of a public-facing web authentication flow by design.

Authentication Bypass

Halo Surface Signal: 5 out of 5 — more likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

This advisory concerns an authentication bypass vulnerability in a component that integrates with Apple for user sign-ins, potentially allowing unauthorized account access. The issue arises from the component not fully validating key information within the authentication token provided by Apple, which could enable attackers to impersonate legitimate users.

Allows attackers to take over user accounts.
Critical for securing user identity and access.
Confirm if this Apple sign-in method is used.

Attack Path

How an attacker could exploit the issue

An attacker can compromise user accounts by spoofing an Apple ID token. This is possible because the system does not fully validate the token's contents before granting access. By reusing or forging specific token parts, an attacker can impersonate any user, leading to account takeover.

Requires no prior authentication.
Relies on unvalidated token claims.
Enables full account takeover.

Live Threat

Current exploitation, exposure, and threat context

This vulnerability could allow an attacker to take over user accounts by replaying stolen or misdirected Apple ID tokens. If the affected authentication component is exposed to the internet, an attacker could authenticate as any user whose Apple ID token has been compromised, even if the token has expired, and impersonate them within the application.

User accounts and associated data.
Replay of stolen Apple ID tokens.
Unauthorized access and account takeover.

Operational Fix

Recommended remediation, mitigation, and detection steps

This vulnerability in ueberauth_apple allows for account takeover due to unvalidated ID token claims, impacting authentication flows. The first practical step is to identify all instances of ueberauth_apple within your environment, assess their reachability and criticality, and pinpoint the accountable application or platform owner for remediation planning.

Application or Platform Owner should drive remediation.
Verify token validation and identify affected applications.
Coordinate vendor updates and plan safe deployments.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is ueberauth_apple?

Ueberauth_apple is an Elixir-based library used within the Ueberauth framework to manage 'Sign in with Apple' authentication. Developers integrate it into web applications to allow users to log in using their Apple credentials. It acts as a bridge, handling the communication and handshake between the application and Apple's identity servers to verify a user's identity.

How does CVE-2026-55954 lead to account takeover?

The vulnerability is an authentication bypass, specifically CWE-290. While the library checks if an Apple token is signed, it fails to verify important token details like expiration or intended audience. Because the library accepts these unvalidated tokens, an attacker can reuse a valid token meant for a different purpose or application to successfully impersonate another user and gain unauthorized access to their account.

Do I need a specific stolen token to trigger this?

Yes. An attacker needs an Apple-signed ID token that includes the target victim's unique user ID. This could be a token they captured or one issued to another application within the same Apple developer team. Crucially, because the software skips expiration checks, even a long-expired token can be used. Normal, correctly generated tokens for your own users do not trigger this, but the logic flaw makes all sessions vulnerable.

Why is this CVE considered internet-facing?

According to Halo Surface Signal, this vulnerability impacts web authentication flows that must be accessible to users over the internet to function. Because the affected code handles login callbacks directly from external identity providers, any application using the vulnerable library version creates a path for remote attackers to interact with the authentication logic without needing prior access.

When should I prioritize fixing CVE-2026-55954?

You should prioritize this immediately if your application uses 'Sign in with Apple.' Your first step is to inventory all services running the affected ueberauth_apple library versions. Once identified, coordinate with your engineering teams to update the dependency to a secure version. Since this flaw allows full account takeover, addressing it is critical for protecting user data and maintaining platform trust.

References

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.