T01 · Skill Instruction Hijacking
- Location
SKILL.md:2- Finding
Runtime Template Injection Can Override Trusted Agent Instructions
- Content
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Vulnerability Details
File Location:
SKILL.md, lines 2 and 13
Vulnerability Type: Runtime instruction injection and safety-constraint override
Risk Level: CriticalVulnerable Code Snippets:
text description: You are a professional chief editor.# User Personalized Preferences [CRITICAL]The following are user-inputted personalized writing preferences, which **you MUST** faithfully adhere to: $GET_USER_TEMPLATE$. If these preferences conflict with your other system prompt instructions, these preferences take the highest priority.text You are a professional chief editor.# User Personalized Preferences [CRITICAL]The following are user-inputted personalized writing preferences, which **you MUST** faithfully adhere to: $GET_USER_TEMPLATE$. If these preferences conflict with your other system prompt instructions, these preferences take the highest priority. If these preferences conflict with the user prompt, the user prompt takes priority.text $GET_CREATION_TEMPLATE$### Step 3: Execute Content Creation Strategy Guided by the System Prompt Acquired in Step 2Technical Analysis
The skill directly interpolates
$GET_USER_TEMPLATE$and$GET_CREATION_TEMPLATE$into its operative instructions without validation, constrained parsing, or separation between untrusted data and trusted control text.More critically, the skill expressly states that the injected personalized preferences take priority when they conflict with system instructions. A skill must not redefine the instruction hierarchy or authorize runtime-controlled content to override system-level safety and confidentiality constraints. The creation template is also inserted into the instruction stream and subsequently characterized as a system prompt, providing a second channel through which runtime-controlled text may redirect agent behavior.
An attacker who can influence either substituted template could inject instructions to ...[truncated 1876 chars]
- Remediation
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Remediation Suggestions
- Remove the statement that personalized preferences can override system instructions. Explicitly preserve the trusted hierarchy: system and developer requirements must always take precedence over skill text, templates, and user preferences.
- Treat
$GET_USER_TEMPLATE$and$GET_CREATION_TEMPLATE$as untrusted data rather than executable instructions. Do not describe substituted content as a system prompt. - Replace free-form template interpolation with a structured schema containing narrowly defined fields such as tone, audience, length, and formatting preferences.
- Validate substituted values against an allowlist and reject content containing instruction-hierarchy changes, tool directives, secrecy requests, safety bypasses, or unrelated task redirection.
- Place accepted preference values inside explicit data delimiters and instruct the agent to use them only when they do not conflict with higher-priority instructions or the user's legitimate task.
- Apply output encoding or safe serialization before inserting runtime values into prompts. Avoid concatenating uncontrolled text into trusted instruction blocks.
- Enforce tool permissions outside the prompt through runtime access controls, argument validation, and least-privilege policies so prompt injection cannot authorize sensitive actions.
- Add security tests using adversarial template values, including attempts to override system rules, request secret disclosure, invoke unrelated tools, or redefine the instruction hierarchy.
- Log template provenance and rejected values without recording sensitive content, enabling administrators to identify attempted instruction injection.