How should we interpret CVSS severity scores?

CVSS estimates technical severity, but it does not automatically equal business risk. Prioritize using context like internet exposure, asset criticality, known exploitation, and whether compensating controls exist. A Medium CVSS on an exposed production system can be more urgent than a Critical on an isolated non-production host.

Vulnerability Database

Q: What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

Q: What's the difference between a vulnerability, an exploit, and a zero-day?

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. Risk increases sharply when exploitation becomes reliable or widespread.

Q: Why do vulnerabilities keep reappearing in our environment?

Recurring findings usually come from incomplete asset discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host.

Q: How do we prioritize remediation without burning out the team?

Use a repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress so remediation is steady, not reactive.

Q: How can SynScan help reduce vulnerability risk over time?

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.

357,869

Total vulnerabilities in the database

CVE-2026-53517 — @better-auth / oauth-provider

Authentication Bypass by Capture-replay

Am I affected?

Users are affected if all of the following are true:

Their project depends on @better-auth/oauth-provider at a version >= 1.6.0, < 1.6.11, or uses the embedded plugin in better-auth >= 1.4.8-beta.7, < 1.6.0.
At least one OAuth client served by their application's authorization server requests the offline_access scope, so refresh tokens are minted.
Concurrent redemption of the same refresh token is reachable: an SPA shares one refresh token across browser tabs without a mutex, a mobile client retries after a transient failure, an attacker who has stolen a refresh token times two requests, or a service worker queues offline requests.

If developer applications do not request offline_access for any client, no refresh tokens are minted and they are not exposed.

Fix:

Upgrade to @better-auth/[email protected] or later.
If developers cannot upgrade, see workarounds below.

Summary

The OAuth provider's POST /oauth2/token endpoint, on the refresh_token grant, performs a non-atomic read / validate / revoke / mint sequence on the oauthRefreshToken row. Two concurrent requests presenting the same parent refresh token both pass the revocation check before either revoke completes, so each mints a fresh refresh token. The replay-detection branch only fires when revoked is already truthy at read time, which is exactly the state concurrent attackers race past. The result is a forked refresh-token family from a single parent token.

Details

The adapter.update predicate on the parent row is keyed on id only; it does not include revoked IS NULL, so two concurrent updates both succeed (last-write-wins, no error path). The schema does not declare unique on oauthRefreshToken.token, so concurrent creates do not collide on a unique-key violation either.

RFC 9700 §4.14 (OAuth Security Best Current Practice) prescribes refresh-token family invalidation on detected reuse; this implementation tries to enforce that contract through the revoked check, but the check is not atomic with the consumption step. Token rotation issues a new refresh token with each call, so a single stolen refresh token grants indefinite access until the row is revoked or its refreshTokenExpiresAt (default 7 days) passes. Rotation refreshes that window each call.

The fix lands an atomic compare-and-swap on the parent row inside the rotation primitive (UPDATE ... WHERE id = ? AND revoked IS NULL with a rowcount check), so the losing rotation fails closed with invalid_grant and the parent row stays marked revoked. Subsequent replay of the original refresh token then trips the existing family-invalidation guard. The schema gains a unique constraint on oauthRefreshToken.token for parity with oauthAccessToken.token.

Patches

Fixed in @better-auth/[email protected]. The refresh-token rotation primitive now performs an atomic compare-and-swap on the parent row, and the explicit revokeRefreshToken path uses the same CAS. On a contested rotation, exactly one caller wins and mints a fresh refresh token; the loser receives invalid_grant. Subsequent replay of the original refresh token trips the existing family-invalidation guard because the parent row stays marked revoked.

@better-auth/[email protected] ships a compatibility fix in the same wave: the in-memory where clause now treats undefined and null as equivalent under an eq null predicate, mirroring SQL IS NULL and Mongo's missing-or-null semantics. Without this change, the CAS predicate WHERE revoked IS NULL falls through on every call against a row whose optional revoked field is absent (the adapter factory's transformInput skips writing undefined when no default exists), so the rotation above is broken for any deployment using the in-memory adapter.

Strict refresh-token family invalidation on a contested rotation, per RFC 9700 §4.14 (which calls for invalidating the winner's tokens too when reuse is detected at rotation time), is deferred to a follow-up minor on the next channel. Closing it cleanly requires an opt-in transactional rotation in the adapter contract so the family-delete cannot interleave with the winner's in-flight access-token insert. The deferred site carries a FIXME(strict-family-invalidation) marker.

Schema-migration note: the better-auth migration generator only emits UNIQUE for newly-created columns. Existing installs will not pick up the new oauthRefreshToken.token unique constraint from migrate / generate; add it manually if an application's operational tooling depends on it (CREATE UNIQUE INDEX oauth_refresh_token_token_uniq ON "oauthRefreshToken" (token);). The CAS fix above does not depend on the database-level constraint to be correct; the constraint is defense-in-depth so collisions from a buggy custom generateRefreshToken callback fail loudly.

Workarounds

None of these close the bug fully without a code patch.

Adapter-level: configure the database adapter to run the OAuth refresh handler under serializable isolation, or wrap the adapter.update on oauthRefreshToken with a row-level pessimistic lock (SELECT ... FOR UPDATE). Narrows the window without closing it.
Token lifetime: pass oauthProvider({ refreshTokenExpiresIn: 60 }) to expire forked families within one minute. Trades attacker persistence for shorter user sessions.
Client-side single-flight: serialize refresh-token usage in the client SDK with a mutex. Mitigates honest concurrency but does nothing against an attacker with a stolen refresh token.
Disable refresh tokens: do not request the offline_access scope. Closes the surface but breaks long-lived sessions.

Impact

Indefinite access from a single stolen refresh token: forked refresh-token families grant access at the original user's authorization scope, surviving past any single revocation if an attacker holds any branch.
Detection bypass: legitimate users whose refresh token has been forked do not trip family invalidation when they refresh, because the attacker's branch already swapped the parent row out from under the legitimate user's check.

Credit

Reported by @chdanielmueller.

Resources

Published: Jul 7, 2026
Updated: Jul 8, 2026
CVE: CVE-2026-53517
GHSA: GHSA-392p-2q2v-4372
Severity: High
Exploit:
CISA KEV:

CVSS v3:

Severity: High
Score: 8.1
AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

CWEs:

OWASP TOP 10:

A2 - Broken Authentication

Affected Software
References

Software	From	Fixed in
@better-auth / oauth-provider	1.6.0	1.6.11
better-auth	1.4.8-beta.7	1.6.0

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Frequently Asked Questions

What is a Vulnerability (CVE) and why does it matter?

A security vulnerability is a weakness in software, hardware, or configuration that can be exploited to compromise confidentiality, integrity, or availability. Many vulnerabilities are tracked as CVEs (Common Vulnerabilities and Exposures), which provide a standardized identifier so teams can coordinate patching, mitigation, and risk assessment across tools and vendors.

CVSS (Common Vulnerability Scoring System) estimates technical severity, but it doesn't automatically equal business risk. Prioritize using context like internet exposure, affected asset criticality, known exploitation (proof-of-concept or in-the-wild), and whether compensating controls exist. A "Medium" CVSS on an exposed, production system can be more urgent than a "Critical" on an isolated, non-production host.

A vulnerability is the underlying weakness. An exploit is the method or code used to take advantage of it. A zero-day is a vulnerability that is unknown to the vendor or has no publicly available fix when attackers begin using it. In practice, risk increases sharply when exploitation becomes reliable or widespread.

Recurring findings usually come from incomplete Asset Discovery, inconsistent patch management, inherited images, and configuration drift. In modern environments, you also need to watch the software supply chain: dependencies, containers, build pipelines, and third-party services can reintroduce the same weakness even after you patch a single host. Unknown or unmanaged assets (often called Shadow IT) are a common reason the same issues resurface.

Use a simple, repeatable triage model: focus first on externally exposed assets, high-value systems (identity, VPN, email, production), vulnerabilities with known exploits, and issues that enable remote code execution or privilege escalation. Then enforce patch SLAs and track progress using consistent metrics so remediation is steady, not reactive.

SynScan combines attack surface monitoring and continuous security auditing to keep your inventory current, flag high-impact vulnerabilities early, and help you turn raw findings into a practical remediation plan.