From 6d9d199350b81524c6ec7faca96ac11df1701172 Mon Sep 17 00:00:00 2001
From: ghost <49853598+JSONbored@users.noreply.github.com>
Date: Sun, 12 Jul 2026 06:57:26 -0700
Subject: [PATCH] fix(miner): write acceptance criteria safely

---
 .../gittensory-miner/lib/coding-task-spec.js  | 24 +++++++++++++++---
 test/unit/miner-coding-task-spec.test.ts      | 25 ++++++++++++++++++-
 2 files changed, 44 insertions(+), 5 deletions(-)

diff --git a/packages/gittensory-miner/lib/coding-task-spec.js b/packages/gittensory-miner/lib/coding-task-spec.js
index ea77ee5bb..46e531508 100644
--- a/packages/gittensory-miner/lib/coding-task-spec.js
+++ b/packages/gittensory-miner/lib/coding-task-spec.js
@@ -1,5 +1,5 @@
-import { writeFileSync } from "node:fs";
-import { join } from "node:path";
+import { closeSync, constants as fsConstants, openSync, realpathSync, writeFileSync } from "node:fs";
+import { isAbsolute, join, relative } from "node:path";
 import {
   ACCEPTANCE_CRITERIA_FILENAME,
   buildAcceptanceCriteria,
@@ -108,10 +108,26 @@ export function buildCodingTaskAcceptanceCriteria(issue, feasibility) {
  * @param {import("@jsonbored/gittensory-engine").AcceptanceCriteria} acceptanceCriteria
  * @returns {{ written: boolean, path: string | null }}
  */
+function assertContainedPath(root, path) {
+  const relativePath = relative(root, path);
+  if (relativePath === "" || (!relativePath.startsWith("..") && !isAbsolute(relativePath))) return;
+  throw new Error(`Refusing to write acceptance criteria outside the worktree: ${path}`);
+}
+
 export function writeAcceptanceCriteriaFile(workingDirectory, acceptanceCriteria) {
   if (!shouldWriteAcceptanceCriteria(acceptanceCriteria.verdict)) return { written: false, path: null };
-  const path = join(workingDirectory, ACCEPTANCE_CRITERIA_FILENAME);
-  writeFileSync(path, serializeAcceptanceCriteria(acceptanceCriteria), "utf8");
+  const root = realpathSync(workingDirectory);
+  const path = join(root, ACCEPTANCE_CRITERIA_FILENAME);
+  assertContainedPath(root, path);
+
+  let fd;
+  try {
+    fd = openSync(path, fsConstants.O_WRONLY | fsConstants.O_CREAT | fsConstants.O_EXCL | fsConstants.O_NOFOLLOW, 0o600);
+    writeFileSync(fd, serializeAcceptanceCriteria(acceptanceCriteria), "utf8");
+  } finally {
+    if (fd !== undefined) closeSync(fd);
+  }
+
   return { written: true, path };
 }
 
diff --git a/test/unit/miner-coding-task-spec.test.ts b/test/unit/miner-coding-task-spec.test.ts
index d587f4aca..d7639cbd4 100644
--- a/test/unit/miner-coding-task-spec.test.ts
+++ b/test/unit/miner-coding-task-spec.test.ts
@@ -1,4 +1,4 @@
-import { mkdtempSync, readFileSync, rmSync } from "node:fs";
+import { mkdtempSync, readFileSync, rmSync, symlinkSync, writeFileSync } from "node:fs";
 import { tmpdir } from "node:os";
 import { join } from "node:path";
 import { afterEach, describe, expect, it, vi } from "vitest";
@@ -171,6 +171,29 @@ describe("writeAcceptanceCriteriaFile (#5132)", () => {
     const result = writeAcceptanceCriteriaFile(dir, doc);
     expect(result).toEqual({ written: false, path: null });
   });
+
+  it("REGRESSION: refuses to follow a pre-existing acceptance-criteria symlink", () => {
+    const dir = tempDir();
+    const outside = join(tempDir(), "victim-config.txt");
+    writeFileSync(outside, "keep-me", "utf8");
+    symlinkSync(outside, join(dir, "acceptance-criteria.json"));
+    const feasibility = buildCodingTaskFeasibility("acme/widgets", issue(), { issues: [issue()], pullRequests: [] }, claimLedger());
+    const doc = buildCodingTaskAcceptanceCriteria(issue(), feasibility);
+
+    expect(() => writeAcceptanceCriteriaFile(dir, doc)).toThrow();
+    expect(readFileSync(outside, "utf8")).toBe("keep-me");
+  });
+
+  it("refuses to overwrite a pre-existing acceptance-criteria file", () => {
+    const dir = tempDir();
+    const path = join(dir, "acceptance-criteria.json");
+    writeFileSync(path, "keep-me", "utf8");
+    const feasibility = buildCodingTaskFeasibility("acme/widgets", issue(), { issues: [issue()], pullRequests: [] }, claimLedger());
+    const doc = buildCodingTaskAcceptanceCriteria(issue(), feasibility);
+
+    expect(() => writeAcceptanceCriteriaFile(dir, doc)).toThrow();
+    expect(readFileSync(path, "utf8")).toBe("keep-me");
+  });
 });
 
 describe("buildCodingTaskSpec (#5132)", () => {