Summary
System Informer before 4.0.26241.138 contains an incorrect authorization flaw in the phsvc helper. A local attacker who can run code from an Authenticode-signed process may access privileged APIs and potentially execute code with SYSTEM-level privileges.
System Informer before 4.0.26241.138 contains an incorrect authorization flaw in the phsvc helper. A local attacker who can run code from an Authenticode-signed process may access privileged APIs and potentially execute code with SYSTEM-level privileges.
Affected context
The vulnerability occurs in deployments of System Informer where the phsvc helper exposes the SiSvcApiPort interface and authorizes callers primarily based on whether they originate from an Authenticode-signed process. The security boundary may be insufficient when an attacker can load or execute code within a trusted signed host process.
The vulnerability occurs in deployments of System Informer where the phsvc helper exposes the SiSvcApiPort interface and authorizes callers primarily based on whether they originate from an Authenticode-signed process. The security boundary may be insufficient when an attacker can load or execute code within a trusted signed host process.
Exploit preconditions
- Attack surface: The local SiSvcApiPort interface exposed by the phsvc helper
- Required access: Local ability to execute code and operate a process signed by a trusted publisher
- Trigger point: Invocation of privileged APIs such as PhSvcApiCreateService
- Why exploitation is possible: Authorization relies on an inadequate caller-trust condition, allowing an attacker-controlled execution context within a signed process to reach privileged functionality
- Attack surface: The local SiSvcApiPort interface exposed by the phsvc helper
- Required access: Local ability to execute code and operate a process signed by a trusted publisher
- Trigger point: Invocation of privileged APIs such as PhSvcApiCreateService
- Why exploitation is possible: Authorization relies on an inadequate caller-trust condition, allowing an attacker-controlled execution context within a signed process to reach privileged functionality
Why this happens
The underlying defect is an authorization decision that treats process signature status as sufficient proof of caller legitimacy. This maps to CWE-863: Incorrect Authorization, because the helper permits access to privileged operations without reliably establishing that the requesting code is authorized to perform them. Trusting a signed host process does not necessarily establish the identity, integrity, or intent of the code executing within that process.
The underlying defect is an authorization decision that treats process signature status as sufficient proof of caller legitimacy. This maps to CWE-863: Incorrect Authorization, because the helper permits access to privileged operations without reliably establishing that the requesting code is authorized to perform them. Trusting a signed host process does not necessarily establish the identity, integrity, or intent of the code executing within that process.
Potential impact
- A local attacker may create or modify services with elevated privileges
- Arbitrary code could execute in the SYSTEM security context
- The attacker could bypass intended local privilege boundaries
- Host confidentiality, integrity, and availability could be compromised
- The compromised system could be used to access additional enterprise resources
- A local attacker may create or modify services with elevated privileges
- Arbitrary code could execute in the SYSTEM security context
- The attacker could bypass intended local privilege boundaries
- Host confidentiality, integrity, and availability could be compromised
- The compromised system could be used to access additional enterprise resources
General mitigation guidance
Mitigation typically focuses on enforcing authorization based on authenticated caller identity and demonstrated privilege rather than process signature alone.
Common defensive patterns include:
- Requiring strong client authentication for privileged helper interfaces
- Authorizing individual operations using least-privilege policy checks
- Separating trusted broker functionality from attacker-influenced code execution contexts
- Validating caller identity, token attributes, and process integrity through independent signals
- Restricting service-creation and other privileged APIs to narrowly defined administrative roles
- Applying defense-in-depth controls such as service installation monitoring and endpoint policy enforcement
These patterns reduce reliance on a signed host as the sole authorization boundary.
Mitigation typically focuses on enforcing authorization based on authenticated caller identity and demonstrated privilege rather than process signature alone.
Common defensive patterns include:
- Requiring strong client authentication for privileged helper interfaces
- Authorizing individual operations using least-privilege policy checks
- Separating trusted broker functionality from attacker-influenced code execution contexts
- Validating caller identity, token attributes, and process integrity through independent signals
- Restricting service-creation and other privileged APIs to narrowly defined administrative roles
- Applying defense-in-depth controls such as service installation monitoring and endpoint policy enforcement
These patterns reduce reliance on a signed host as the sole authorization boundary.
How teams detect issues like this
Organizations commonly detect related authorization weaknesses through:
- Static analysis and code review of named ports, IPC endpoints, and privileged broker interfaces
- Checks for authorization decisions based only on executable signatures, image paths, or process names
- Review of service-creation APIs and other privileged operations exposed to local clients
- Endpoint telemetry for unexpected connections to SiSvcApiPort or unusual service creation by signed host processes
- Policy enforcement that alerts on unsigned or untrusted code executing within approved host processes
Automated security review tools can help identify trust-boundary violations and insufficient caller validation.
Organizations commonly detect related authorization weaknesses through:
- Static analysis and code review of named ports, IPC endpoints, and privileged broker interfaces
- Checks for authorization decisions based only on executable signatures, image paths, or process names
- Review of service-creation APIs and other privileged operations exposed to local clients
- Endpoint telemetry for unexpected connections to SiSvcApiPort or unusual service creation by signed host processes
- Policy enforcement that alerts on unsigned or untrusted code executing within approved host processes
Automated security review tools can help identify trust-boundary violations and insufficient caller validation.
