Summary
Authorizer: Zero-click account takeover via OAuth identity linking to unverified email accounts
The OAuth callback handler links incoming OAuth identities (Google, GitHub, etc.) to existing accounts matched by email address without verifying that the existing account's email was verified by its original owner. An attacker who pre-registers with a victim's email address (without verifying it) gains persistent password-based access to the victim's account after the victim completes a normal OAuth login. Verified against HEAD (commit 73679fa).
Root Cause
In internal/http_handlers/oauth_callback.go, when an OAuth login occurs for an email that already exists in the database:
Line 125: The existing user is looked up by email:
existingUser, err := h.StorageProvider.GetUserByEmail(ctx, refs.StringValue(user.Email))
Line 164: The OAuth user object is replaced with the existing user:
user = existingUser
Lines 173-176: The OAuth provider is appended to the existing user's signup methods:
signupMethod := existingUser.SignupMethods
if !strings.Contains(signupMethod, provider) {
signupMethod = signupMethod + "," + provider
}
user.SignupMethods = signupMethod
Lines 179-181: If the existing account's email was NOT verified, it is automatically verified:
if user.EmailVerifiedAt == nil {
now := time.Now().Unix()
user.EmailVerifiedAt = &now
}
Line 219: The merged user is saved to the database:
user, err = h.StorageProvider.UpdateUser(ctx, user)
At no point is the existing account's password invalidated or the owner notified that a new OAuth identity was linked.
Attack Chain
Attacker signs up with
[email protected]using email/password. Attacker sets a known password but does NOT click the email verification link. The account exists in the database withEmailVerifiedAt = nil.Some time later, the real owner of
[email protected]logs in via Google OAuth (a completely normal action).The OAuth callback at line 125 finds the attacker's existing account by email.
At line 164, the Google OAuth identity is linked to the attacker's account.
At line 179-181, the email is automatically verified (the attacker never verified it, but now it's marked as verified).
At line 175, "google" is appended to the signup methods. The account now has both "basic_auth" and "google" as valid login methods.
The attacker's original password is still valid in the database. It was never cleared, changed, or invalidated.
The attacker logs in with
[email protected]and the password they originally set. They now have full access to the victim's account, including any data the victim added via their Google session.
Why This Is Zero-Click
The victim performs no unusual action. They simply log in via their Google account, which is the expected, secure behavior. The attacker staged the account beforehand and gains access without any further interaction.
This is a classic Account Linking vulnerability (cited in OWASP authentication guidelines). The core logic flaw is a trust boundary violation. Authorizer correctly trusts that Google has verified the email address, but it incorrectly extends that trust to validate the password that was set by the unverified attacker. The attacker maintains persistent, password-based backdoor access to the victim's account, even if the victim later revokes Authorizer's OAuth access from their Google account settings. The password was set before Google was ever involved and is never invalidated by the linking process.
Credit
Koda Reef
Impact
- Full account takeover for any user who logs in via OAuth
- Attacker maintains persistent password-based access even after the victim changes OAuth providers
- All data the victim creates after OAuth login is accessible to the attacker
- The victim has no indication their account was pre-staged
- Affects every OAuth provider configured in Authorizer (Google, GitHub, Facebook, Apple, LinkedIn, Twitter, Discord, Twitch, Roblox, Microsoft)
The application does not adequately verify the identity of a user, device, or process before granting access. Typical impact: unauthorized access to functions or data reserved for authenticated parties.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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Before linking an OAuth identity to an existing account, verify that the existing account's email is already verified:
existingUser, err := h.StorageProvider.GetUserByEmail(ctx, refs.StringValue(user.Email))
if err == nil {
// Account exists. Only link if email is already verified.
if existingUser.EmailVerifiedAt == nil {
// Email not verified by original owner. Do NOT link.
// Either: reject the login, or create a new separate account,
// or delete the unverified account and create a fresh one for the OAuth user.
}
}
Additionally, when linking a new OAuth identity, invalidate any existing password on the account or require the user to re-authenticate via the original method.
Frequently Asked Questions
- What is CVE-2026-35511? CVE-2026-35511 is a high-severity improper authentication vulnerability in github.com/authorizerdev/authorizer (go), affecting versions < 0.0.0-20260807033110-66fe488fd2a4. It is fixed in 0.0.0-20260807033110-66fe488fd2a4. The application does not adequately verify the identity of a user, device, or process before granting access.
- Which versions of github.com/authorizerdev/authorizer are affected by CVE-2026-35511? github.com/authorizerdev/authorizer (go) versions < 0.0.0-20260807033110-66fe488fd2a4 is affected.
- Is there a fix for CVE-2026-35511? Yes. CVE-2026-35511 is fixed in 0.0.0-20260807033110-66fe488fd2a4. Upgrade to this version or later.
- Is CVE-2026-35511 exploitable, and should I be worried? Whether CVE-2026-35511 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-35511 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-35511? Upgrade
github.com/authorizerdev/authorizerto 0.0.0-20260807033110-66fe488fd2a4 or later.