dsh-egress-guard

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A runtime security gate for DeepSeek Harness tool calls.

Existing security plugins in the ecosystem scan configuration files before an agent runs. This one sits in the tool-execution pipeline and acts on the calls themselves:

Rule	Extension point	What it does
Egress allowlist	tools/pre-execute	Denies (or asks about) a call that names a network destination outside your allowlist — curl to a paste site, git push to an unknown remote, a fetch to an exfiltration endpoint.
Secret redaction	tools/post-execute	Rewrites credentials out of a tool result before the model, the durable session log, or a Code Mode program can read them.
Audit log	both waterfalls	Appends every decision — including the ones monitor mode only would have made — to a JSONL file.

No fork, no patched loop: three listeners on documented extension points, disposed cleanly on unload.

Install

dsh plugin --profile <name> add dsh-egress-guard

The bundle ships mode: monitor, so installing it cannot break a working setup: every rule is evaluated and audited, nothing is blocked or rewritten. Read the audit log for a day, then turn on enforcement in your profile's cordis.patch.yml:

- id: egress-guard
  config:
    mode: enforce
    egress:
      enabled: true
      allowHosts: ['*.github.com', '*.npmjs.org', 'api.deepseek.com']
      denyHosts: []
      allowLoopback: true
      onViolation: deny
    redact:
      enabled: true
      builtins: true
      extraPatterns: []
      placeholder: '[redacted:{name}]'
    audit:
      enabled: true
      path: ''
      logAllowed: false

A patch replaces a row's whole config, so restate every key you want to keep.

Configuration

Key	Default	Meaning
mode	monitor	off registers nothing. monitor evaluates and audits without acting. enforce denies and redacts.
egress.allowHosts	[] in schema, a starter list in the bundle	Permitted hosts. *.example.com covers the apex and every subdomain. An empty list means denylist-only.
egress.denyHosts	[]	Always denied. Beats allowHosts and allowLoopback.
egress.allowLoopback	true	Exempts localhost, 127.0.0.0/8, ::1, *.localhost.
egress.onViolation	deny	ask routes to ctx.approval instead — and degrades to deny when no approval service is mounted.
redact.builtins	true	Private keys, vendor API keys, JWTs, bearer headers, KEY=value assignments.
redact.extraPatterns	[]	Extra regex sources, compiled with the global flag.
redact.placeholder	[redacted:{name}]	{name} is the pattern that matched.
audit.path	$DSH_HOME/egress-guard.jsonl	JSONL, one decision per line.
audit.logAllowed	false	Also record calls that named a host and passed — this is how you build an allowlist out of real traffic.

Building an allowlist from real traffic

# 1. Install (monitor mode) and work normally for a while, with logAllowed: true.
# 2. See which hosts your agent actually reaches:
jq -r '.hosts[]?' ~/.dsh/egress-guard.jsonl | sort | uniq -c | sort -rn
# 3. Put the legitimate ones in allowHosts, then flip mode to enforce.

Design notes

Redaction happens at the canonical value, not the rendered content. The registry's contract is explicit that content replacement is not a confidentiality boundary — a Code Mode program receives the canonical value directly. So a successful result is redacted by replacing its value, and the content is re-rendered from the redacted value. Failed results carry no value (the registry rejects a value replacement on them), so their message is redacted as content.

The guard runs last in the post-execute waterfall. It delegates with next() first, then redacts whatever projection the composed decision actually carries, so a listener deeper in the waterfall cannot reinstate the original text. When another plugin replaced the content but the underlying value holds a secret, the guard replaces the value — losing that plugin's presentation, but not leaking to programmatic consumers. That precedence is deliberate.

Denials tell the model not to route around them. A bare "denied" invites a retry with a different tool; the reason string names the hosts and says to ask the user instead.

Limitations — read this before trusting it

This is a guard rail, not a containment boundary. It raises the cost of an accident or a careless prompt injection; it does not stop a determined adversary running code on your machine.

• Detection is textual. Destinations are found by scanning argument strings for URLs and user@host remotes. A command that assembles its destination at runtime (curl "$ENDPOINT", base64, string concatenation, an IP in decimal form) is invisible to the gate. Real containment is the sandbox seam's job (dsh-bash-sandbox, network namespaces, a proxy), not a string matcher's.
• A tool that opens its own socket bypasses the gate entirely unless the destination appears in its arguments.
• Redaction is pattern-based, so it misses credential shapes it does not know, and it can rewrite text that merely looks like a secret. Add extraPatterns for your own formats; check the audit log for false positives before enforcing.
• Binary content is not scanned — image blocks and other non-text blocks pass through untouched.
• The audit log is local and unsigned. Anything that can write to your filesystem can edit it.

Compatibility

Built against the @deepseek-ai/dsh-tools 0.1.0-rc pipeline contract and verified two ways: the test suite runs against 0.1.0-rc.6 from npm, and the plugin was booted in a real dsh 0.1.0-rc.5 profile, reaching fiberPhase: active.

Note that npm's latest tag for the @deepseek-ai/* packages still points at an old 0.0.1-rc.1 line; the current releases are on the next tag. If you install harness packages by hand, ask for the version explicitly.

The harness is in developer preview and states that compatibility-breaking changes will happen. If a pipeline contract shifts, this plugin's tests are designed to fail loudly — they execute real calls through a real registry rather than mocking the waterfalls.

Development

npm install
npm test          # 61 tests: pure unit tests + end-to-end through a real ToolRuntime
npm run typecheck
npm run build

To try it against a live harness without publishing:

dsh plugin --profile <name> add /path/to/dsh-egress-guard
dsh --profile <name> --dump-config   # shows the "# == dsh-egress-guard" layer

License

MIT