CVE-2026-49757 Vulnerability Analysis & Exploit Details

CVE-2026-49757 Vulnerability Summary

CVE-2026-49757: Authentication Bypass by Spoofing vulnerability in team-alembic AshAuthentication allows account takeover of local users via OAuth2/OIDC sign-in. AshAuthentication's OAuth2 and OIDC family strategies matched the local user by email address (an upsert on the email field, or a user-defined sign-in filter) rather than by the OpenID Connect iss/sub claim combination. Per OpenID Connect Core §5.7, only iss/sub uniquely and stably identifies an end-user; other claims, including email, MUST NOT be used as unique identifiers. A provider login presenting a victim's email, including an unverified email, a reused email, or an account with email_verified: false, resolved to and signed in as the victim's existing local account. An unauthenticated attacker who can register an account on any accepted OAuth provider with the victim's email (or who benefits from provider-side email reuse or reclamation) obtains the victim's full local privileges. The fix resolves users by the (strategy, sub) identity stored in a user identity resource, and only links a new sub to an existing local account by email when the provider's email_verified claim is trusted (trust_email_verified?). This issue affects ash_authentication from 0.1.0 before 4.14.0 and from 5.0.0-rc.0 before 5.0.0-rc.10.

CVE-2026-49757 References

External References

• https://cna.erlef.org/cves/CVE-2026-49757.html
• https://github.com/team-alembic/ash_authentication/commit/64530644f9b37ebb76ca14aeb83a77597a0034b7
• https://github.com/team-alembic/ash_authentication/commit/728b8d28c1b5f465fa1116ef044a815300fc733d
• https://github.com/team-alembic/ash_authentication/security/advisories/GHSA-777c-2fxx-qr28
• https://osv.dev/vulnerability/EEF-CVE-2026-49757

CWE Common Weakness Enumeration

CAPEC Common Attack Pattern Enumeration and Classification

• Exploitation of Trusted Identifiers CAPEC-21 An adversary guesses, obtains, or "rides" a trusted identifier (e.g. session ID, resource ID, cookie, etc.) to perform authorized actions under the guise of an authenticated user or service.
• Exploiting Trust in Client CAPEC-22 An attack of this type exploits vulnerabilities in client/server communication channel authentication and data integrity. It leverages the implicit trust a server places in the client, or more importantly, that which the server believes is the client. An attacker executes this type of attack by communicating directly with the server where the server believes it is communicating only with a valid client. There are numerous variations of this type of attack.
• Creating a Rogue Certification Authority Certificate CAPEC-459 An adversary exploits a weakness resulting from using a hashing algorithm with weak collision resistance to generate certificate signing requests (CSR) that contain collision blocks in their "to be signed" parts. The adversary submits one CSR to be signed by a trusted certificate authority then uses the signed blob to make a second certificate appear signed by said certificate authority. Due to the hash collision, both certificates, though different, hash to the same value and so the signed blob works just as well in the second certificate. The net effect is that the adversary's second X.509 certificate, which the Certification Authority has never seen, is now signed and validated by that Certification Authority.
• Web Services API Signature Forgery Leveraging Hash Function Extension Weakness CAPEC-461 An adversary utilizes a hash function extension/padding weakness, to modify the parameters passed to the web service requesting authentication by generating their own call in order to generate a legitimate signature hash (as described in the notes), without knowledge of the secret token sometimes provided by the web service.
• Signature Spoof CAPEC-473 An attacker generates a message or datablock that causes the recipient to believe that the message or datablock was generated and cryptographically signed by an authoritative or reputable source, misleading a victim or victim operating system into performing malicious actions.
• Signature Spoofing by Misrepresentation CAPEC-476 An attacker exploits a weakness in the parsing or display code of the recipient software to generate a data blob containing a supposedly valid signature, but the signer's identity is falsely represented, which can lead to the attacker manipulating the recipient software or its victim user to perform compromising actions.
• Session Credential Falsification through Prediction CAPEC-59 This attack targets predictable session ID in order to gain privileges. The attacker can predict the session ID used during a transaction to perform spoofing and session hijacking.
• Reusing Session IDs (aka Session Replay) CAPEC-60 This attack targets the reuse of valid session ID to spoof the target system in order to gain privileges. The attacker tries to reuse a stolen session ID used previously during a transaction to perform spoofing and session hijacking. Another name for this type of attack is Session Replay.
• Bluetooth Impersonation AttackS (BIAS) CAPEC-667 An adversary disguises the MAC address of their Bluetooth enabled device to one for which there exists an active and trusted connection and authenticates successfully. The adversary can then perform malicious actions on the target Bluetooth device depending on the target’s capabilities.
• Adversary in the Middle (AiTM) CAPEC-94 An adversary targets the communication between two components (typically client and server), in order to alter or obtain data from transactions. A general approach entails the adversary placing themself within the communication channel between the two components.

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