T09 · Insecure Skill Coding Practices
- Location
references/how-tos/system.md:257- Finding
Untrusted Local Configuration Is Transformed into Executable PECMD Code
- Content
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Vulnerability Details
File Location:
references/how-tos/system.md:257-260
Vulnerability Type: Arbitrary command execution through unsafe dynamic code evaluation
Risk Level: Highwcs READ %CurDir%\rules.ini,**,&A SED &&A=0:0,%&NA%,%&NA%ENVI ,{*ENVI %A% // convert lines to ENVI commands SET< A=%&NL%} %&A% // execute generated code blockTechnical Analysis
This example reads
%CurDir%\rules.iniinto a variable, transforms its lines into PECMD statements, and executes the generated code through%&A%. It does not validate the file's ownership, permissions, integrity, syntax, or permitted operations.Consequently, configuration data crosses directly into a code-execution sink. If
%CurDir%orrules.iniis writable by an untrusted user or process, arbitrary PECMD directives can be injected. Input filtering is especially difficult here because PECMD supports command chaining, external program execution, dynamic script loading, registry modification, storage operations, and network functionality.The issue is particularly significant in WinPE environments, where PECMD commonly runs with
SYSTEMprivileges.Attack Path
- A victim incorporates the documented dynamic-code pattern into a PECMD tool or startup workflow.
- An attacker gains write access to
%CurDir%\rules.ini, or controls the working directory from which the script runs. - The attacker inserts malicious PECMD directives into
rules.ini. READimports the attacker-controlled content.SEDconverts the imported lines into a generated PECMD code block.%&A%evaluates the generated block without validation.- The injected directives execute with the privileges of the PECMD process.
Impact Assessment
Successful exploitation provides arbitrary PECMD command execution under the current process identity. If PECMD is running as
SYSTEM, the attacker may obtain system-level execution.The r ...[truncated 517 chars]
- Remediation
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Remediation Suggestions
- Do not evaluate configuration files as PECMD source code.
- Parse
rules.inias data using a strict schema and map each supported key to a fixed, allowlisted operation. - Reject unknown keys, malformed values, command separators, script directives, external execution directives, and dynamic loading constructs.
- Use an absolute trusted path rather than
%CurDir%, which may vary or be attacker-controlled. - Restrict the configuration file and its parent directory with ACLs so only trusted administrators or the owning service identity can modify them.
- Verify file integrity or a cryptographic signature before processing when configurations are distributed or stored outside a protected image.
- Run the consuming tool with the minimum privileges necessary rather than
SYSTEMwhenever possible. - If dynamic execution is unavoidable, isolate it in a restricted process and permit only a narrowly defined command subset after canonicalization and validation.
- Fail closed on validation, integrity, ownership, or permission errors, and record rejected configuration attempts in security logs.