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Security audit

microsoft-teams-mcp

Security checks for vulnerabilities and agentic risk

Overview

ClawScan marked this skill suspicious because its read-focused purpose is paired with shell helpers that can make state-changing Teams requests and send an authorization header to other destinations if their arguments are controlled.

Consider avoiding installation until the helper's request options are restricted to approved read operations, the write instructions are removed or clearly separated behind approval, and the missing tool scope is clarified. The scan is partial: although all three listed components were scanned, several local references could not be resolved, so the evidence is incomplete.

Vulnerability Patterns
  • Skill Instruction HijackingAlters the agent's session goals or safety constraints when the skill loads
  • Agent Memory PoisoningWrites attacker-controlled rules into memory that affect later sessions
  • Remote Payload Retrieval and ExecutionFetches external code whose behavior can change after review
  • Embedded Malicious CodeShips malicious scripts inside the skill and executes them locally
  • Unauthorized Access and Privilege EscalationObtains permissions beyond the task's legitimate needs
Vulnerability Patterns
  • Tool MisuseTool Parameter Abuse, Chaining Abuse, Unsafe Defaults
  • MCP Least PrivilegeUnderdeclared Capability, Wildcard Permission, Missing Permission Declaration
  • MCP Tool PoisoningHidden Instructions, Unicode Deception, Parameter Description Injection
  • Prompt InjectionInstruction Override, Hidden Instructions, Exfiltration Commands
  • Data ExfiltrationExternal Transmission, Env Variable Harvesting, File System Enumeration
Findings (6)

Chaining Abuse

High
Category
Tool Misuse
Confidence
75% confidence
Finding

Tool calls are chained to bypass individual safety checks or escalate capabilities beyond what any single tool call would allow.

Content

Scanner excerpt · references/teams-env.sh (reported line 107)May include surrounding context.

sh
args=(-s -K "$rc_file" -H 'behavioroverride: redirectAs404'
        -o "$tmp" -w '%{http_code}' --max-time 60)
  http_status="$(curl "${args[@]}" "$@" "$url")" || {
    echo "curl failed" >&2; rm -f "$tmp"; return 1; }

  case "$http_status" in
    2*) cat "$tmp"; rm -f "$tmp"; return 0 ;;

Chaining Abuse

High
Category
Tool Misuse
Confidence
75% confidence
Finding

Tool calls are chained to bypass individual safety checks or escalate capabilities beyond what any single tool call would allow.

Content

Scanner excerpt · references/teams-env.sh (reported line 110)May include surrounding context.

sh
echo "curl failed" >&2; rm -f "$tmp"; return 1; }

  case "$http_status" in
    2*) cat "$tmp"; rm -f "$tmp"; return 0 ;;
    401) echo "401 — token expired or revoked. Run: teams_token_refresh" >&2
         rm -f "$tmp"; return 4 ;;
    *)  echo "HTTP $http_status" >&2; sed -n '1,5p' "$tmp" >&2; rm -f "$tmp"; return 4 ;;

Chaining Abuse

High
Category
Tool Misuse
Confidence
75% confidence
Finding

Tool calls are chained to bypass individual safety checks or escalate capabilities beyond what any single tool call would allow.

Content

Scanner excerpt · references/teams-env.sh (reported line 113)May include surrounding context.

sh
2*) cat "$tmp"; rm -f "$tmp"; return 0 ;;
    401) echo "401 — token expired or revoked. Run: teams_token_refresh" >&2
         rm -f "$tmp"; return 4 ;;
    *)  echo "HTTP $http_status" >&2; sed -n '1,5p' "$tmp" >&2; rm -f "$tmp"; return 4 ;;
  esac
}

Skill declares no tool scope ('permissions' or 'allowed-tools') but code capabilities were detected: env, file_read, shell.

Medium
Category
MCP Least Privilege
Confidence
70% confidence
Finding

Without declared permissions the skill's intent is opaque and cannot be validated.

Content

No source excerpt is available for this finding.

The read-focused skill includes instructions for writing Teams messages and reactions.

Medium
Category
Excessive Agency
Confidence
93% confidence
Finding

The manifest describes reading Teams data, but this section supplies POST and PUT endpoints for sending messages and adding reactions using the captured bearer token. Requiring approval for each post reduces risk but does not reconcile these remote-write instructions with the manifest's read-focused scope.

Content

No source excerpt is available for this finding.

Helpers documented as read-only permit state-changing Teams API requests through unrestricted curl arguments.

Medium
Category
Excessive Agency
Confidence
99% confidence
Finding

The purportedly read-only helpers forward arbitrary arguments to authenticated curl, allowing callers to supply methods and bodies such as -X POST and --data to perform state-changing Teams requests. Additional URL arguments can also send the configured Authorization header to an unapproved destination, so the primary-URL allowlist does not fully protect the bearer token; exploitation requires control over arguments passed to the helper.

Content

No source excerpt is available for this finding.