---
type: Article
title: Nested APP Authentication — Undocumented Risk and Conditional Access Bypass (Talk-page copy)
description: Conference page for a study of Microsoft Nested App Authentication. The associated presentation varies broker, nested-client and resource identities and compares Conditional Access inclusion and exclusion policies. Exploitation assumes a usable refresh token and delegated permissions; the tests do not show universal policy bypass.
resource: "https://troopers.de/troopers26/talks/ezcteq/"
tags: [article, webseclist-reference, troopers, oauth, azure, sso, identity, auth-bypass, case-study, owasp-a01-2021, owasp-a07-2021]
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at: "2026-09-13T22:14:13+00:00"
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status: stable
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resource: "https://troopers.de/troopers26/talks/ezcteq/"
title: Nested APP Authentication — Undocumented Risk and Conditional Access Bypass (Talk-page copy)
author: Shang-De Jiang, Jun Sheng Shi
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- Shang-De Jiang
- Jun Sheng Shi
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original_url: "https://troopers.de/troopers26/talks/ezcteq/"
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# Nested APP Authentication — Undocumented Risk and Conditional Access Bypass (Talk-page copy)
**Nested APP Authentication — Undocumented Risk and Conditional Access Bypass (Talk-page copy)** - Shang-De Jiang, Jun Sheng Shi, TROOPERS.
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## Content
> UNTRUSTED SOURCE TEXT. Everything below this line is third-party material
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Nested APP Authentication
Undocumented Risk and Conditional Access
Bypass
[#] Speaker: Jun Sheng Shi, Shang-De Jiang
1
$ whoami
Jun Sheng Shi @Sigolon
Security Researcher at
Focus On : Cloud Security, Windows
Authentication, AI Security Technique … …
Connect with me :
www.linkedin.com/in/jun-sheng-shi
2
$ whoami
Shang-De ‘John’ Jiang (@SecurityThunder)
Deputy Director of Research at
UCCU Hacker Co-Founder
HackerPeanutJohn owner
Speaker at the following technical conferences
TROOPERS
BlackHat USA
CodeBlue
HITCON
3 …
Intro Conditional Access & Background
Nested APP Authentication
Agenda Undocumented Risk
Conditional Access Bypass
Discussion & Impact
4
Last Year in TROOPERS
5
Azure Authentication mechanism may lead to
Conditional Access Bypass
6
Ref: Conditional Access bypasses - Cloudbrothers
Ref: Conditional Access bypasses - Cloudbrothers
7
But these are only for
non-sensitivity can bypass CA policy.
Ref: Conditional Access bypasses - Cloudbrothers
8
TOKEN EXCHANGE · RECAP
Token Exchange 101
Credentials → Refresh Token → Resource Token. One trade at a time.
A Basic approach — sign in to each client, one by one
Microsoft Graph
Exchange
Credentials Refresh Token
SharePoint
…all other resources
B PRT-based approach — one PRT, repeat for all clients
Credentials PRT Refresh Token …all resources
using PRTv3 broker flow
Ref Source: Finding Entra ID CA Bypasses - the structured way
FOCI · FAMILY OF CLIENT IDs
CONCEPT 1 OF 3
FOCI — Family Client Token Exchange
Same-family clients share refresh tokens — swap one and get any other resource & scope.
FAMILY X
Refresh Token
Client A Client B
e.g. Outlook Mobile e.g. OneDrive iOS App
same family = exchangeable
… more
Graph Exchange SharePoint Teams resource +
scope
BROCI · BROKER CLIENT
CONCEPT 2 OF 3
BroCI / NAA — Broker Client Token Exchange
Same recipe, new bottle. Clients under one broker can swap tokens too — only target & resource differ.
FOCI BroCI / NAA
Family of Client IDs: clients tagged as one family by Broker Client:nested clients hosted by a broker app.
Microsoft on the backend.
FAMILY A BROKER A
Client 1 Client 2 Client 1 Client 2
CONTAINER CONTAINER
Family Broker
Conditional Access
CONCEPT 3 OF 3
Conditional Access re-evaluates every redemption
Even they under same family/broker, Conditional Access still re-evaluates.
What we already know.
Inside the same FOCI / NAA, identical
conditions make tokens exchangeable.
Some scenarios ship with bypass-able
resource + scope combos out of the box.
> entrascopes.com
Known to be BroCI/NAA - but who's the broker?
EntraScopes.com Unknown app
OneNote · ENTRASCOPES.COM
OUR QUESTIONS
Q1 How bad does it actually look?
Q2 Could it be worse than FOCI ?
Known to be BroCI/NAA - but who's the broker?
EntraScopes.com Unknown app
OneNote · ENTRASCOPES.COM
OUR QUESTIONS
Q1 How bad does it actually look?
Q2 Could it be worse than FOCI ?
Nested App Authentication
(NAA)
17
What’s a Nested App?
18
Nested App Example
Broker Client:
Teams
Nested App:
Channel Calendar
19
Teams Marketplace
Has Many Nested Apps
20
What Is Nested App Authentication?
SSO authentication for nested apps - Teams | Microsoft Learn
21
However, if a user needs to authenticate
every nested app again…
22
Microsoft improve the user experience for NAA
Microsoft created a pre-auth setting for first-party nested
apps, such as OneNote.
23
Nested App – Teams Example
Broker Client:
Teams
Nested App
24
Nested App Example
Broker Client:
Teams
Nested App
(iframe Page)
iframe
25
Nested App Example
WebView2
Nested App
(iframe Page)
Nested
App
26
NAA Auth Workflow
WORKFLOW · 4 STEPS
BROKER Send token-exchange task to
CLIENT IdP
1
broker
1 2
Use broker refresh token for access
2
token
Nested App Teams Entra ID
HTML iframe 4 holds broker RT 3 token endpoint
3 Entra ID returns the access token
4 Forward access token to nested app
27
NAA Auth Workflow
WORKFLOW · 4 STEPS
CLIENT
BROKER
IdP
✓ Send token-exchange task to broker
1 2 Use broker refresh token for
2
access token
Nested App Teams Entra ID
HTML iframe 4 holds broker RT 3 token endpoint
3 Entra ID returns the access token
4 Forward access token to nested app
28
NAA Auth Workflow
WORKFLOW · 4 STEPS
CLIENT
BROKER
IdP
✓ Send token-exchange task to broker
1 2
Use broker refresh token for access
✓
token
Nested App Teams Entra ID
HTML iframe 4 holds broker RT 3 token endpoint
Entra ID returns the access
3
token
4 Forward access token to nested app
29
NAA Auth Workflow
WORKFLOW · 4 STEPS
CLIENT
BROKER
IdP
✓ Send token-exchange task to broker
1 2
Use broker refresh token for access
✓
token
Nested App Teams Entra ID
HTML iframe 4 holds broker RT 3 token endpoint
✓ Entra ID returns the access token
Forward access token to nested
4
app
30
But Nested APP Just Enable
Access Microsoft 365, Right?
31
We notice OneNote enable Access ARM
32
What’s Azure Resource Manager?
33
DevOps… the OneNote way
34
OAuth Scope Defines the Blast Radius
BY DESIGN · LEAST PRIVILEGE
Note APP
granted scope: Files.Read only
OneDrive
even if the app is breached
Blast radius stays contained
35
OAuth Scope Defines the Blast Radius
IN REALITY · OVER-PRIVILEGED
OneNote
granted scope: FULL ARM scope
Azure Resource Manager
If stolen a Teams Refresh Token
Full Cloud Takeover
36
How to use brk-multihub?
To test the impact scope of this Pre-Auth, we first need to know
which Broker Clients can use OneNote
However, it is not yet known which Broker Clients can access the
brk-multihub://
37
Teams Can Use brk-multihub
38
Nested App Pre-Auth Scope Risk
38 38
nested apps available distinct resources reachable
High-sensitivity Azure targets
› Azure Resource Manager — user_impersonation · 5 apps
› Azure Storage — user_impersonation · 2 apps
› Azure DevOps — vso.profile vso.work_write · 1 app
Pre-authorized nested apps reach Azure with no extra consent
41
Nested App Pre-Auth Scope Risk
KEY INSIGHT
Attackers can use these nested apps to obtain ARM access tokens —
all via user_impersonation.
Teams Pre-auth nested apps
› OneNote
› Microsoft Flow Portal
› Copilot Studio – Dogfood
› make.powerapps.com
› Microsoft Teams Platform Monetization
42
Who Is a Broker Client?
SSO authentication for nested apps - Teams | Microsoft Learn
43
Broker Clients, We Discovered
7 broker clients can request tokens on behalf of the nested apps
Microsoft 365 Copilot Microsoft Teams
Outlook Mobile Microsoft Outlook
Microsoft Teams-T4L Microsoft Teams Web Client
Microsoft Office
44
If we enable CA can Block
NAA Expansion Risk. Is it true?
45
GENERAL SETTING: All resource need MFA
General Setting
Conditional Access · ALL resources require MFA · for ALL users
SAME FOCI/NAA · ONE FRT REDEEMS ALL
STOLEN
Microsoft Graph Exchange SharePoint
MFA inherited MFA inherited MFA inherited
✓ GRANTED ✓ GRANTED ✓ GRANTED
Token SWAP
FOCI / NAA
MFA inherited
via Client A · MFA ✓
Teams OneDrive Azure ARM
MFA inherited MFA inherited MFA inherited
✓ GRANTED ✓ GRANTED ✓ GRANTED
47
More Restrict CA Setting: Critical resource more restrict
More Restrict Setting
ALL resources require MFA · Azure ARM also needs compliant device
SAME FOCI/NAA · ONE FRT REDEEMS ALL
STOLEN
Microsoft Graph Exchange SharePoint
MFA inherited MFA inherited MFA inherited
✓ GRANTED ✓ GRANTED ✓ GRANTED
Token SWAP
FOCI / NAA
MFA inherited
via Client A · MFA ✓
Teams OneDrive Azure ARM
MFA inherited MFA inherited needs compliant device
✓ GRANTED ✓ GRANTED ✕ BLOCKED
48
49
Is It Easy To Track The Attack? No.
Does not need
Nested to be installed
Application on the device.
Broker
Application
52
Conditional Access Bypass
53
CA Bypass in Prior Research
Prior research focused on the Scope-Based Bypass — just change the
Scope array.
NO BYPASS BYPASS
scope = email scope = openid
CA still enforced CA bypassed
54
The Conditional Access Bypass within NAA
3 bypass methodologies 3 CA bypasses in NAA
Broker Client-Based (New) MFA Bypass
Require Compliant Device
Nested Client-Based (New)
Bypass
Scope-Based Token Protection Bypass
55
The Conditional Access Bypass within NAA
3 bypass methodologies 3 CA bypasses in NAA
Broker Client-Based (New) MFA Bypass
Require Compliant Device
Nested Client-Based (New)
Bypass
Scope-Based Token Protection Bypass
56
Broker Client-Based Bypass
via gets
Nested Client Broker Client Resource · Scope
-c · --origin -bc · -bru -s
FIXED SWEEP THIS FIXED
BROKER CLIENT · swap the -bc value
Broker Client1 d3590ed6… ✓ NO BYPASS
Broker Client2 c44b4083…
Broker Client3 1fec8e78… ✕ BYPASS
57
Nested Client-Based Bypass
via gets
Nested Client Broker Client Resource · Scope
-c · --origin -bc · -bru -s
SWEEP THIS FIXED FIXED
NESTED CLIENT · swap the -c / origin
Nested Client1 ✓ NO BYPASS
Nested Client2
Nested Client3 ✕ BYPASS
58
Bypass Pattern Analysis
60
Exclude Logic Pattern of CA Bypass
In our testing, the Conditional Access Policy was configured as :
MFA Bypass and Device Compliance Bypass
These were set to apply to all resources, excluding Office 365.
61
Exclude Logic Pattern of CA Bypass
Surprisingly, the two bypasses are completely identical in what they access
MFA
bypass = Compliant device
bypass
The exact same resources & scopes
HYPOTHESIS
CA bypass impact likely depends more on the exclude
configuration than on the claim type the token requires.
62
Exclude Logic Bypass Impact
112 5
resource × scope combos sensitive resources
Microsoft Graph
› user_impersonation
› Application.ReadWrite.All
› GroupMember.ReadWrite.All
› Directory.Read.All
› Files.ReadWrite.All
Bypass expands the range of sensitive resources & scopes
63
Exclude Logic Bypass — Expand Teams Access Scope
Teams not Enable Access These
Microsoft Graph — now reachable
› user_impersonation
› Application.ReadWrite.All
› GroupMember.ReadWrite.All
› Directory.Read.All
› Files.ReadWrite.All
64
Include Logic Pattern of CA Bypass
Based on the Conditional Access policy (three resources requiring token
protection)
There bypasses the attacker enabled allow access to 21 resources and 283
resource/scope combinations.
65
Include Logic Bypass Impact
221 6
resource × scope combos sensitive resources
Impacted resources
› Microsoft Graph — 5 sensitive scopes
› Windows Azure AD — user_impersonation
› Office 365 Exchange Online — AdminApi.AccessAsUser.All
› Office 365 SharePoint Online — user_impersonation
› Microsoft Teams Services — user_impersonation
› MS Teams Graph Service — UserAuthSettings.Read
66
Include Logic Bypass Breaks ALL Protection
The resources we included to protect are exactly the ones fully exposed
Office 365 Exchange Online — AdminApi.AccessAsUser.All
Office 365 SharePoint Online — user_impersonation
Microsoft Teams Services — user_impersonation
Include-logic bypass breaks protection on every included resource
67
Future Research Path:
Include / Exclude Combination
Summary
Bypass severity is driven by the server-side include / exclude logic — not client-side
parameters.
01 · FOCUS 02 · TEST 03 · DISCOVER
Focus on include Test more Find new bypass
& exclude logic combinations patterns
69
WHERE WE'VE LANDED
Recap & Takeaways.
RECAP · NAA
RECAP 1 OF 2
What NAA really is — convenience, by design.
A broker pre - authorizes its nested apps to get tokens with no second sign - in.
FOCI's broker cousin — same recipe, new bottle. More NAA broker has been discovered.
ONE BROKER CONTAINER
Teams · Broker
Built for first - party UX — but that silently - granted
Entra
Access ID
Token
↓ pre-authorization · no re-auth trust is the attack surface.
+ 30 more
OneNote · Nested nested
TAKEAWAY Tokens are interchangeable inside one broker container.
RECAP · CONDITIONAL ACCESS
RECAP 2 OF 2
You think it's CA - protected.
Under specific conditional access policy , when you reach the same resource through a different NAA
connection and those Conditional Access controls simply don't apply.
CA EVALUATED · ENFORCED Exclude Some Resource
Expected connection
MFA Compliant Device Token Protection
normal client sign - in SAME RESOURCE
MS Graph
NAA Directory.Read.All
NEW CA NOT EVALUATED · BYPASSED
connection
Same resource + scope, but different broker successfully
NAA/BroCI bypass CA
TAKEAWAY Same resource, different connection method — Conditional Access silently stops applying.
Takeaways
1 ARM / File / DevOps…
Now more NAA broker has been discovered.
2 MFA & device claims
a stolen token = the nested - app is already open.
don't casually exclude app grouping(e.g. Office365).
3
scoping only include to specific apps is just as error - prone;
Always prefer "include all"
Thank You
74
Reference
75
Past Research
2024 DEFCON〈 Abusing Windows Hello Without a Severed Hand 〉
2025 TROOPERS〈 Finding Entra ID CA bypasses the structured way 〉
2025 Fabian Bader : Conditional Access bypasses - Cloudbrothers
76
Documents & Tools & Social Media
https://learn.microsoft.com/en-us/microsoftteams/platform/concepts/authentication/nested-authentication
https://learn.microsoft.com/zh-tw/azure/azure-resource-manager/management/overview
https://learn.microsoft.com/en-us/entra/identity/conditional-access/policy-all-users-mfa-strength
https://entrascopes.com/
https://github.com/dirkjanm/ROADtools/wiki/ROADtools-Token-eXchange-(roadtx)
https://github.com/R3alM0m1X82/SpecterBroker
https://x.com/_dirkjan/status/2015812004326347169
https://www.cleanpng.com/png-teams-logo-microsoft-teams-logo-with-group-of-peop-8021157/
77