Enhancing MCP Security: Combating Insecure Credential Storage Vulnerabilities

Insecure Credential Storage in MCP: A Practical Guide to Fixing the Problem

Insecure credential storage in Model Context Protocol (MCP) tooling is more than a design flaw - it is an open invitation for attackers to siphon API keys, hijack sessions, and move laterally across connected systems. Recent research from Trail of Bits lays out two common pathways that leave secrets world‑readable on disk or buried in chat logs, both trivially collectible with commodity malware or file‑read exploits (Trail of Bits blog). Below is a concise breakdown of the risk, real‑world examples, and the steps Nox90 recommends to secure your environment.

Overview of the Vulnerability

Long‑lived API keys for services such as Google Maps, Postgres, or GitLab are often written in plaintext within MCP servers and desktop agents. Default file permissions (-rw-r--r-- or even 0666) let every local user or process read them, violating CWE‑256 guidance on clear‑text credential storage (MITRE CWE‑256).

How Does Insecure Credential Storage Happen?

Pathway	Detail
1. Insecure configuration files	MCP servers persist credentials to JSON config files in the user’s home directory. If the host’s umask is permissive, any user or malware can copy the keys in seconds (Trail of Bits).
2. Credentials leaked via chat logs	Several desktop MCP clients let users paste tokens directly into AI chat windows. Conversation histories are stored on disk and often inherit world‑readable permissions.

Spotlight on the Figma MCP server - The community connector stores API tokens with 0666 permissions, making them readable (and writable) by the whole system, paving the way for session‑fixation attacks (Figma MCP guide).

Real‑World Exploitation Scenarios

Vector	Example	Impact
Local malware scanning predictable paths	Infostealers harvest claude_desktop_config.json and similar files.	Credential exfiltration, lateral movement
Arbitrary file‑read bugs in unrelated software	Exploits in vulnerable software read secrets from /home/<user>/…key files.	Privilege escalation, data breach
Shared workstations or CI runners	Other users on the host simply cat the config file.	Insider threat
Misconfigured cloud backups	Public S3 buckets expose exported config archives.	Mass credential exposure

Defense‑in‑Depth: Mitigation Strategies

1. Use short‑lived, scoped tokens - Implement OAuth 2.1; tokens that expire quickly slash the blast radius if stolen.

2. Leverage operating‑system secret stores

   
   

   • Windows: Credentials Management API.

   • macOS: Keychain Services.

   • Linux: Secret Service API.

   
   

3. Adopt dedicated secrets‑management platforms - HashiCorp Vault provides encrypted at‑rest storage, dynamic credentials, and policy‑based access control.

4. Lock down file permissions - If legacy components must store tokens on disk, enforce mode 0600, verify ownership, and audit regularly.

5. Educate users and review third‑party integrations - Never paste tokens in chats; audit community MCP servers (e.g., Figma) for secure‑by‑default practices.

Nox90 Recommendations

Our Secure Software Development Lifecycle (SSDLC) program embeds these controls:

1. Secure design reviews - We analyze every MCP or API connector for credential‑handling flaws before deployment.

2. Automated secrets scanning - CI pipelines flag plaintext keys and over‑permissive file modes.

3. Secrets‑rotation playbooks - We guide teams migrating to OAuth or Vault without downtime.

4. Continuous monitoring - Telemetry detects abnormal token use that signals theft.

Questions about hardening your MCP stack or broader application security concerns? Contact the Nox90 team at info@nox90.com – we are ready to help.

Further Reading

• Jumping the Line: How MCP servers can attack you before you ever use them – Trail of Bits

• How MCP servers can steal your conversation history – Trail of Bits

By replacing long‑lived plaintext secrets with scoped tokens, backing them with proven OS keyrings or Vault, and enforcing strict file permissions, organizations can shut down a class of attacks that currently plague MCP environments. Nox90 is committed to guiding you from assessment to remediation so your developers can innovate without exposing the keys to the kingdom.

Nox90 is here for you

Nox90 is committed to providing comprehensive application security solutions and SSDLC practices to help our clients mitigate risks like those posed by insecure credential storage. We are happy to answer any questions you might have about this report or any other issues at info@nox90.com.