dsh-dlp

dsh-dlp

Data-loss prevention for DeepSeek Harness, built as an out-of-repo plugin.

📖 Full documentation

What it does

1. Denies credential-file access and secrets bound for the network — unconditionally, from ctx.tools.guard(), testing path-typed arguments against a table of credential stores and following symlinks first.
2. Redacts secrets out of tool results before the model reads them and before the session log records them, withholding a result it cannot clean.
3. Redacts secrets out of the messages a step enters with — the context a listener splices in (the workspace AGENTS.md/CLAUDE.md chain, a captured tmux pane, a hook's additionalContext, a skill body a /name token loaded) and the input the loop claimed from the inbox that the user did not type (a dsh-webhook delivery's third-party payload, a settled subagent result, an agent relay). All of it reaches the model and the durable log through agent/pre-step without ever being a tool result. A message whose source.kind is user is exempt below aggressiveness: high; at high the user's own typed prompt is redacted too, because this plugin cannot know which provider the request is bound for. The agent/inbox/spliced delivery record keeps a delivery's original text, which is deliberate — it derives no model message, and an operator investigating a webhook incident needs to read what was actually delivered.
4. Redacts secrets out of exported telemetry, closing a hole where DSH_TELEMETRY_MODE=FULL ships message text, tool arguments, results and workspace paths in the clear.
5. Detects payment card numbers — issuer range, a length that issuer assigns, and a Luhn check digit — so cardholder data does not reach a third-party model in a tool result, a spliced file, exported telemetry, or (at aggressiveness: high) a prompt someone typed.
6. Detects the harness's own Web Host session credential — the dsh-auth- browser cookie and the 43-character launch token that mints it. Whoever holds either is an authenticated caller of the Host API that drives the agent. DeepSeek Harness Desktop is an Electron shell around the Web application, so under Desktop that credential always exists; the CLI composition this plugin was first built against runs no web server and has neither.
7. Strips invisible characters that carry hidden instructions — the Tags block, bidi overrides, runs of variation selectors — and strips terminal control sequences from the audit lane so a tool result cannot forge its own audit record.
8. Neutralises remote markdown images in assistant output and detects a tool call another plugin rewrote after the session log recorded it.
9. Asks before the agent writes a file that changes future behaviour — agent settings and hooks, CLAUDE.md, .claude/rules/** and the other agent rules directories, prompt templates, .vscode/tasks.json, .mcp.json, git hooks, CI workflows, shell startup files, pnpm-workspace.yaml — and before it writes a *_BASE_URL that would redirect a provider credential.
10. Asks before a call switches off its own confirmation — non_interactive: true, approval_mode: auto, an apply whose approval is still pending. Both ask tiers are prompts rather than controls: they live at tools/pre-execute, they can be neutralised, and they abstain wherever the approval seam prompts nobody — which includes every install under DSH_PERMISSION_MODE=danger-full-access and a stock headless install under any mode.
11. Writes an audit record for every decision. A redaction or denial names the rule, its version, the offsets and a keyed hash; the three kinds with no matched region to describe — an ask, a rewritten call, a neutralised image — carry a rule id, the changed field names or the destination hostname instead. Never the secret, never the path or command that matched. dsh-dlp report reads it back.

What this is not

This is not a containment boundary. The plugin runs in-process, at the agent's own uid. Anything the agent can execute — a bash command, a run_code program, a mounted MCP server — can read every file the guard denies and open its own sockets without the plugin seeing anything. It closes the path where the model asks for credential material through a tool. It does not stop code that is already running. If you need containment, that is the sandbox, landlock-run, filesystem permissions and egress firewalling.

Three limits worth knowing before you rely on it:

• Only the guard floor is unconditional. Every other seam can be neutralised by a listener registered ahead of ours. ctx.tools.guard() is order-independent only because it has no allow arm. Result redaction registers with { prepend: true } so it gets the last word over listeners already registered — but a listener registering after it with the same option lands ahead of it again.
• The shell-command arm is advisory pattern-matching. It tests the whole command line and each of its tokens, so a credential path left spelled in the command is caught whatever program would open it: python3 -c "open('~/.ssh/id_rsa')" is denied. Changing the spelling defeats it — one glob character, quote-splitting, find -exec, a substitution that assembles the path from pieces, a base64 round-trip, each verified. Do not count this arm as a control.
• Detection is pattern-based. No entropy rule (measured, not assumed: the lowest false-positive-free threshold cannot flag anything shorter than 64–66 characters). Encoded forms pass. A homoglyph defeats every rule in this package. The card rule is Luhn-validated and range-checked and found nothing across 272,635 lines of real source and docs, but a uniformly random 16-digit number trips it 2.7% of the time and Maestro is not covered.

The full list of limits →

Under DeepSeek Harness Desktop

Desktop is an Electron shell around the Web application, not around the CLI. Its profile mounts the Web bundle plus a bundled Python/LibreOffice runtime and the three Office skills, so three things change for this plugin and only one of them is closed here.

• Closed. The Web Host's session credential now has a detector (item 6 above). Under the CLI composition there was no web server, so there was nothing to detect.
• Covered already, by the existing seams. Document text the agent extracts with the bundled python-docx/openpyxl/python-pptx arrives as a tool result and is redacted there. So does the structural checker's JSON, load_workspace_dependencies' path report, and a past session's transcript that session-reference splices into a step — that last one only because this plugin registers its agent/pre-step listener after the bundle does, which is the ordering caveat above and not a guarantee.
• Not covered, and not closeable from here. The Office skills tell the model to render document pages to PNG with the bundled LibreOffice kit and read them back with read_image. An image content block carries an attachment reference and no text, so there is nothing for a text detector to scan: a card number or a credential printed inside a .docx reaches the model as pixels. Neither is Electron's userData directory on the credential-path table — it holds the Host cookie jar — because the Host child process is never told where it is.

Install

A profile carrying only @deepseek-ai/dsh-base has no agent loop, so add a runnable bundle alongside it or there is nothing for this plugin to guard:

dsh plugin --profile <name> add @deepseek-ai/dsh-headless@0.1.0-rc.6
dsh plugin --profile <name> add dsh-dlp
dsh --profile <name> --dump-config      # the dsh-dlp row should appear

Any harness from 0.1.0-rc.6 onwards in the 0.1.x line works, prereleases included. CI drives the end-to-end suite against every published rc the peer ranges admit — 0.1.0-rc.6, rc.7, rc.8, 0.1.1-rc.1, 0.1.1-rc.2. The 0.1.2 prerelease line is watched by a non-blocking job line without running it end to end.

Pin @deepseek-ai/dsh-headless explicitly — its npm latest tag still points at 0.0.1-rc.1. The package ships a cordis.patch.yml bundle layer, so listing it in dsh.profile.bundles mounts it with working defaults.

Install from the registry or a packed tarball, not from a git spec: lib/ is a build output git does not carry and no prepare script rebuilds it, so a git-spec row mounts and then fails to load.

Configure

- id: dsh-dlp
  config:
    auditLog: /var/log/dsh-dlp.audit.jsonl
    redactionKeyFile: /var/lib/dsh/dsh-dlp.redaction-key
    policyFile: ./.dsh-dlp.yml        # optional, lowest trust
    aggressiveness: medium            # low | medium | high
    breadthTier: true
    resultRedaction: true
    telemetryRedaction: true
    stepContextRedaction: true
    claimedInputRedaction: true
    configWriteAsk: true
    approvalSuppressionAsk: true

redactionKeyFile is created on first mount with 32 random bytes at mode 0600. Keep it out of version control — it is what makes a placeholder's hash keyed rather than a bare digest anyone holding a candidate secret could confirm.

aggressiveness is one word for how far redaction reaches. low guarantees nothing and lets each toggle stand alone; medium — the default — guarantees every pass is on and that no toggle can take one away; high adds the user's own typed prompt to what is redacted. It composes with the toggles rather than overriding them: at medium and high a toggle set to false contradicts the level and fails the mount with the fix in the message, rather than one setting quietly beating the other.

Upgrading from 0.9.0. The default medium matches the shipped toggle defaults exactly, so an install that never wrote a toggle is unchanged. An install that set any redaction toggle to false now refuses to mount; add aggressiveness: low to the same row and it means what it meant before. high is opt-in.

The guard floor has no configuration. Credential-path denial and secret-argument denial are security invariants, not deployment-varying tunables. A repo-local policyFile is the lowest trust rank and may only tighten: add deny patterns, add egress tool names, raise a severity, switch a pass on. It cannot reach aggressiveness — raising the level would let a hostile workspace put placeholders into the user's own prompt. Any downgrade makes the whole file invalid.

Configuration reference → · What gets denied → · Redaction and detection →

Reading the audit log

dsh-dlp report                       # everything in the audit sink
dsh-dlp report --since 24h
dsh-dlp report --session <id>
dsh-dlp report --would-have          # everything except the denials

A redaction or denial record carries a rule id, rule version, span offsets and a keyed hash — never the matched value. An ask carries its rule id, a rewritten call the names of the fields that changed, and a neutralised remote image the destination hostname in the clear; none of those has a matched region to hash.

Audit record format →

Mitigations for defects in the harness itself

Three registrations work around defects in DeepSeek Harness rather than in your configuration: remote markdown images in assistant output, a tool call rewritten between tools/pre-execute and the guard, and a telemetry redactor that cannot run under the shipped default. None of them closes its channel and an upstream fix is better in all three cases.

What each one does and does not close →

Development

nvm use 22           # Node ^22.19.0 || >=24, and pnpm 11
pnpm install
pnpm run typecheck
pnpm run test:coverage
pnpm run test:e2e    # boots a real dsh against a mock model; no API key

test:e2e needs a harness to boot. It defaults to a checkout at ../dsh, which must have its dependencies installed, build:lib:host run, and native/system built; DSH_CLI points it at an installed dsh bin instead. It cannot currently run against the 0.1.7 line even though the peer range admits it: the pinned mock server speaks /chat/completions and that line's adapter speaks /v1/messages. ADR §34 records the options and why none was chosen unilaterally.

Coverage is gated at 100% per file: this is a security control, so an untested branch in a deny path is an unproven deny path.

Design decisions and their rationale live in ADR.md. Security policy is in SECURITY.md.

License

MIT