APPSEC-INSTAGRAM-OTP-BRUTEFORCE-2019

nOAuth, disclosed by Descope's security team on June 20, 2023 (reported to Microsoft on April 11, 2023), is a cross-tenant account-takeover class in multi-tenant Microsoft Entra ID (Azure AD) OAuth applications, mapping to OWASP API2:2023 Broken Authentication. The flaw existed because Entra ID emitted an 'email' claim in the OIDC token that was both mutable and unverified, while applications used that email rather than the immutable 'sub'/'oid' claim to identify and link the signed-in user. An attacker who controlled their own Entra tenant could set the email attribute of an attacker account to a victim's email address, then use 'Log in with Microsoft' against any vulnerable app; the app merged accounts by the spoofed email and granted full control of the victim's account, requiring no interaction from the victim. Descope confirmed real exposure in major SaaS apps including a design platform with millions of monthly users. Microsoft mitigated by no longer emitting unverified email claims by default for app registrations created after June 2023 and added the xms_edov claim and a RemoveUnverifiedEmailClaim flag.

On May 5, 2021 Pen Test Partners researcher Jan Masters and TechCrunch publicly disclosed that Peloton's API exposed the private account data of its users, having been reported privately to Peloton on January 20, 2021. The API had endpoints, including a workout-details POST endpoint, a user-search GET endpoint, and GraphQL endpoints, that performed no authorization checks: unauthenticated requests returned account data such as user IDs, location/city, age, gender, weight, workout statistics, birthday, and group/studio attendance, even for users who had set their profiles to private, because the privacy flag was not enforced at the API layer. This is a missing/insufficient-authorization flaw on an API serving over 3 million subscribers' data. A partial fix on February 2, 2021 only restricted the API to authenticated Peloton members, so anyone willing to create an account could still pull any other user's private data until the full fix around early May.

On September 28, 2018 Facebook disclosed that attackers had stolen access tokens by exploiting its View As feature; an initial estimate of nearly 50 million affected accounts was revised on October 12, 2018 to about 30 million whose tokens were actually stolen (roughly 29 million had data accessed). The root cause was a business-logic flaw chaining three bugs in the read-only View As profile preview: a video-uploader composer added in July 2017 wrongly appeared in that view, it incorrectly minted an access token at all, and critically it minted the token for the user being viewed rather than the viewer, embedding that token in the page HTML. An attacker could therefore select View As a target and scrape a fully privileged token for the target account, then pivot through friend lists to harvest tokens outward from roughly 400,000 seed accounts. The flaw is an improper-authentication / business-logic failure where an auth credential was generated in the wrong context and scoped to the wrong principal.

A source map (.map) is a build artifact that maps minified bundle code back to the original source, and bundlers embed the full original code in its sourcesContent field. Left reachable in production or shipped inside a package, it hands anyone the unminified codebase, internal comments, hidden API endpoints, auth logic, and any secrets that were compiled in. Discovery is trivial: open DevTools and read the Sources tab, request the bundle's .map URL directly, or Google-dork for ext:map intext:webpack, then reconstruct the whole project with a tool like unwebpack-sourcemap. Passive scanners such as Acunetix and Burp already flag it as a standalone finding. It is usually rated medium on its own but escalates fast when the recovered source contains live credentials or undocumented endpoints; exposed Webpack source maps have leaked hardcoded Stripe secret keys that enabled unauthorized payments. High-profile cases include Apple's App Store web front-end in November 2025, shipped with source maps still enabled, and Anthropic's Claude Code, whose entire TypeScript source leaked via a source map left in a published npm package in March 2026.

GraphQL servers expose three abuse primitives stemming from the query language's flexibility. Leaving introspection enabled lets any client send a __schema query and recover the entire type system, including internal admin mutations and deprecated fields, providing a map of the attack surface (OWASP API8/API2). Because per-request rate limiters count one HTTP request regardless of operations inside it, an attacker can use field aliasing (e.g. attempt0:login(...), attempt1:login(...)) or array batching to pack dozens of login or verifyOtp mutations into a single request, brute-forcing credentials or short OTP/2FA codes while the rate limiter sees only one request; this aliasing-bypass technique is reproduced in the PortSwigger Web Security Academy 'Bypassing GraphQL brute force protections' lab and Wallarm's GraphQL batching research. Deeply nested or recursive queries cause an exponential explosion of resolver and database calls, exhausting CPU, memory and connection pools for denial of service, the core of OWASP API4:2023 Unrestricted Resource Consumption. HackerOne has disclosed a real GraphQL authentication-bypass finding, and Apollo Server v4 disabled array batching by default in response to these attacks.

A business-logic race condition exploits the brief window between a check on shared state and the act that mutates it (time-of-check to time-of-use), letting concurrent requests each pass the same check before any of them commits, so a limited resource is consumed more times than allowed (OWASP API6:2023, Unrestricted Access to Sensitive Business Flows). The vulnerable code is any check-then-act sequence on shared state without atomic database-level locking: validate a single-use coupon or gift card then redeem it, check a balance then withdraw or transfer, or verify a one-per-user limit then grant. Firing many near-simultaneous requests collapses the state machine and redeems one coupon multiple times, withdraws the same balance twice, or bypasses a per-user cap. James Kettle's 'Smashing the state machine: the true potential of web race conditions' (PortSwigger, published 9 August 2023, presented at Black Hat USA and DEF CON 31) introduced the single-packet attack, which withholds the final HTTP/2 frames of 20-30 requests and releases them in one TCP packet, neutralizing network jitter and squeezing arrivals into a sub-millisecond window so the race becomes reliably exploitable.