T01 · Skill Instruction Hijacking
- Location
SKILL.md:12- Finding
Remote Highest-Priority Instruction Hijacking
- Content
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Vulnerability Details
File Location:
SKILL.md, lines 12–15
Vulnerability Type: Remote instruction control through a mutable external document
Risk Level: CriticalVulnerable Code
markdown ⚠️ STOP — You MUST read and strictly follow the shared runtime rules before proceeding. Do NOT select or call any tool until all rules are read. These rules have the highest priority. → Read [gate-runtime-rules.md](https://github.com/gate/gate-skills/blob/master/skills/gate-runtime-rules.md) - **Only call MCP tools explicitly listed in this skill.** Tools not documented here must NOT be called, even if they exist in the MCP server.Technical Analysis
The Skill directs the agent to retrieve and obey instructions from an external GitHub document, explicitly declaring those instructions to have “the highest priority.” The URL targets the mutable
masterbranch rather than an immutable commit, and the referenced document is not included in the audited artifact.Consequently, the effective Skill behavior is not fully represented by the reviewed project files. Anyone able to modify the referenced repository content—or compromise the repository or its maintainers—could change the instructions followed by agents without modifying this Skill package. The external document could attempt to alter confirmation requirements, redirect tool usage, request sensitive information, or supersede locally reviewed safeguards.
This is instruction hijacking rather than remote code execution: the artifact retrieves remote Agent instructions, but the audit found no mechanism that downloads and executes external program code.
Attack Path
- A user invokes the Gate spot-trading Skill.
- The agent processes
SKILL.md. - Lines 12–14 instruct the agent not to proceed until it retrieves the external runtime-rules document.
- An attacker with control over the referenced repository path changes the document on the mutable
masterbranch. - The agent loads th ...[truncated 1096 chars]
- Remediation
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Remediation Suggestions
- Bundle the shared runtime rules as a local file inside the reviewed Skill artifact.
- Replace the mutable external URL with a local relative path.
- If remote retrieval is operationally unavoidable:
- Pin the reference to an immutable commit.
- Verify the downloaded content against an expected cryptographic hash.
- Reject the content if verification fails.
- Remove the assertion that external Skill content has “the highest priority.”
- State explicitly that Skill and remote instructions cannot override system instructions, developer policies, security controls, or user-authorization requirements.
- Fail closed when the runtime rules are missing, unreachable, changed, or unverifiable.
- Include the pinned runtime-rules file in future security audits and release reviews.
- Preserve mandatory immediate-turn confirmation gates for every financial write regardless of any externally supplied instruction.