Potential Azure Browser SSO Abuse

Severity: low
Author: Den Iuzvyk
Source: upstream

Detects abusing Azure Browser SSO by requesting OAuth 2.0 refresh tokens for an Azure-AD-authenticated Windows user (i.e. the machine is joined to Azure AD and a user logs in with their Azure AD account) wanting to perform SSO authentication in the browser. An attacker can use this to authenticate to Azure AD in a browser as that user.

MITRE ATT&CK coverage

Tactic	Techniques
Persistence	`T1574.001` Hijack Execution Flow: DLL
Privilege Escalation	`T1574.001` Hijack Execution Flow: DLL
Defense Evasion	`T1574.001` Hijack Execution Flow: DLL

Event coverage

Provider	Event ID	Title
Sysmon	7	Image loaded

Stages and Predicates

Stage 1: `selection`

ImageLoaded: 'C:\Windows\System32\MicrosoftAccountTokenProvider.dll'

Stage 2: `not 1 of filter_main_bgtaskhost`

or:
Image|startswith: 'C:\Windows\SysWOW64\'
Image|startswith: 'C:\Windows\System32\'
Image|endswith: '\BackgroundTaskHost.exe'

Stage 3: `not 1 of filter_optional_*`

or:
or:
Image|endswith: '\msedge.exe'
Image|endswith: '\msedgewebview2.exe'
or:
Image|startswith: 'C:\Program Files (x86)\Microsoft\EdgeCore\'
Image|startswith: 'C:\Program Files\Microsoft\EdgeCore\'
or:
Image|startswith: 'C:\Program Files (x86)\Microsoft Visual Studio\'
Image|startswith: 'C:\Program Files\Microsoft Visual Studio\'
Image|endswith: '\IDE\devenv.exe'
Image|endswith: '\AppData\Local\Microsoft\OneDrive\OneDrive.exe'
Image|endswith: '\WindowsApps\MicrosoftEdge.exe'
Image: 'C:\Program Files (x86)\Internet Explorer\iexplore.exe'
Image: 'C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe'
Image: 'C:\Program Files\Internet Explorer\iexplore.exe'
Image: 'C:\Program Files\Microsoft\Edge\Application\msedge.exe'
Image: null
Image|startswith: 'C:\Program Files (x86)\Microsoft\EdgeWebView\Application\'

Indicators

Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.

Field	Kind	Values
`Image`	ends_with	`\AppData\Local\Microsoft\OneDrive\OneDrive.exe` `\BackgroundTaskHost.exe` `\IDE\devenv.exe` `\WindowsApps\MicrosoftEdge.exe` corpus 12 (sigma 12) `\msedge.exe` corpus 22 (sigma 22) `\msedgewebview2.exe` corpus 15 (sigma 15)
`Image`	eq	`C:\Program Files (x86)\Internet Explorer\iexplore.exe` corpus 10 (sigma 10) `C:\Program Files (x86)\Microsoft\Edge\Application\msedge.exe` corpus 11 (sigma 11) `C:\Program Files\Internet Explorer\iexplore.exe` corpus 11 (sigma 11) `C:\Program Files\Microsoft\Edge\Application\msedge.exe` corpus 11 (sigma 11)
`Image`	starts_with	`C:\Program Files (x86)\Microsoft Visual Studio\` corpus 2 (sigma 2) `C:\Program Files (x86)\Microsoft\EdgeCore\` corpus 11 (sigma 11) `C:\Program Files (x86)\Microsoft\EdgeWebView\Application\` corpus 10 (sigma 10) `C:\Program Files\Microsoft Visual Studio\` corpus 2 (sigma 2) `C:\Program Files\Microsoft\EdgeCore\` corpus 11 (sigma 11) `C:\Windows\SysWOW64\` corpus 16 (sigma 16) `C:\Windows\System32\` corpus 16 (sigma 16)
`ImageLoaded`	eq	`C:\Windows\System32\MicrosoftAccountTokenProvider.dll`