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Security audit

smtping-email-verification

Security checks for vulnerabilities and agentic risk

Overview

This skill is a disclosed SMTPing email verification helper that sends user-provided email addresses to SMTPing for the stated purpose.

Install only if you intend to use SMTPing and are comfortable sending the email addresses you verify to SMTPing's API. Set `SMTPING_API_KEY` yourself, do not paste or expose it in chat, confirm bulk checks before spending credits, and consider pinning or reviewing the MCP package before using the suggested `npx` install path.

A.I.G

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

SkillSpector

Vulnerability Patterns
  • Data ExfiltrationExternal Transmission, Env Variable Harvesting, File System Enumeration
  • Supply ChainUnpinned Dependencies, External Script Fetching, Obfuscated Code
  • Prompt InjectionInstruction Override, Hidden Instructions, Exfiltration Commands
  • Privilege EscalationExcessive Permissions, Sudo/Root Execution, Credential Access
  • Excessive AgencyUnrestricted Tool Access, Autonomous Decision Making, Scope Creep
Findings (10)

External Transmission

Medium
Category
Data Exfiltration
Confidence
60% confidence
Finding

Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.

Content

Scanner excerpt · SKILL.md (reported line 24)May include surrounding context.

md
1. **MCP tools available** (`verify_email`, `verify_list`, `get_bulk_job`, `check_threat`, `get_credits`): use them. They handle retries and bulk polling.
2. **No MCP tools, shell available**: call the REST API with `curl` as shown below.
3. **Neither**: tell the user to install the MCP server (`npx -y @smtping/mcp`, see https://smtping.com/email-verification-mcp) or give them the curl command to run.

## Cost rules

Rp1

Medium
Category
MCP Rug Pull
Confidence
95% confidence
Finding

The skill instructs users to install and execute an MCP server via npx -y @smtping/mcp without pinning a specific version or integrity value. This creates a supply-chain risk: a newly published, compromised, or typo-squatted package version could be fetched and executed automatically, and the -y flag reduces friction for unreviewed execution.

Content

No source excerpt is available for this finding.

External Transmission

Medium
Category
Data Exfiltration
Confidence
50% confidence
Finding

Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.

Content

Scanner excerpt · SKILL.md (reported line 34)May include surrounding context.

md
## REST API

Base URL: `https://api.smtping.com/api/v1`
Auth header on every request: `X-API-Key: $SMTPING_API_KEY`

### One address

External Transmission

Medium
Category
Data Exfiltration
Confidence
50% confidence
Finding

Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.

Content

Scanner excerpt · SKILL.md (reported line 40)May include surrounding context.

md
## REST API

Base URL: `https://api.smtping.com/api/v1`
Auth header on every request: `X-API-Key: $SMTPING_API_KEY`

### One address

External Transmission

Medium
Category
Data Exfiltration
Confidence
50% confidence
Finding

Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.

Content

Scanner excerpt · SKILL.md (reported line 51)May include surrounding context.

md
## REST API

Base URL: `https://api.smtping.com/api/v1`
Auth header on every request: `X-API-Key: $SMTPING_API_KEY`

### One address

External Transmission

Medium
Category
Data Exfiltration
Confidence
50% confidence
Finding

Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.

Content

Scanner excerpt · SKILL.md (reported line 61)May include surrounding context.

md
## REST API

Base URL: `https://api.smtping.com/api/v1`
Auth header on every request: `X-API-Key: $SMTPING_API_KEY`

### One address

External Transmission

Medium
Category
Data Exfiltration
Confidence
50% confidence
Finding

Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.

Content

Scanner excerpt · SKILL.md (reported line 69)May include surrounding context.

md
## REST API

Base URL: `https://api.smtping.com/api/v1`
Auth header on every request: `X-API-Key: $SMTPING_API_KEY`

### One address

External Transmission

Medium
Category
Data Exfiltration
Confidence
50% confidence
Finding

Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.

Content

Scanner excerpt · SKILL.md (reported line 78)May include surrounding context.

md
## REST API

Base URL: `https://api.smtping.com/api/v1`
Auth header on every request: `X-API-Key: $SMTPING_API_KEY`

### One address

External Transmission

Medium
Category
Data Exfiltration
Confidence
50% confidence
Finding

Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.

Content

Scanner excerpt · SKILL.md (reported line 88)May include surrounding context.

md
## REST API

Base URL: `https://api.smtping.com/api/v1`
Auth header on every request: `X-API-Key: $SMTPING_API_KEY`

### One address

External Transmission

Medium
Category
Data Exfiltration
Confidence
60% confidence
Finding

Data is being sent to an external URL. This could be legitimate telemetry or data exfiltration. Manual review is recommended.

Content

Scanner excerpt · SKILL.md (reported line 69)May include surrounding context.

When status is Succeeded, fetch the results:

bash
curl -s https://api.smtping.com/api/v1/verify/bulk/JOB_ID/result \
  -H "X-API-Key: $SMTPING_API_KEY"

Static analysis

No suspicious patterns detected.