diff --git a/src/agents/sandbox/sanitize-env-vars.test.ts b/src/agents/sandbox/sanitize-env-vars.test.ts
new file mode 100644
index 000000000..9367ef551
--- /dev/null
+++ b/src/agents/sandbox/sanitize-env-vars.test.ts
@@ -0,0 +1,57 @@
+import { describe, expect, it } from "vitest";
+import { sanitizeEnvVars } from "./sanitize-env-vars.js";
+
+describe("sanitizeEnvVars", () => {
+  it("keeps normal env vars and blocks obvious credentials", () => {
+    const result = sanitizeEnvVars({
+      NODE_ENV: "test",
+      OPENAI_API_KEY: "sk-live-xxx",
+      FOO: "bar",
+      GITHUB_TOKEN: "gh-token",
+    });
+
+    expect(result.allowed).toEqual({
+      NODE_ENV: "test",
+      FOO: "bar",
+    });
+    expect(result.blocked).toEqual(expect.arrayContaining(["OPENAI_API_KEY", "GITHUB_TOKEN"]));
+  });
+
+  it("blocks credentials even when suffix pattern matches", () => {
+    const result = sanitizeEnvVars({
+      MY_TOKEN: "abc",
+      MY_SECRET: "def",
+      USER: "alice",
+    });
+
+    expect(result.allowed).toEqual({ USER: "alice" });
+    expect(result.blocked).toEqual(expect.arrayContaining(["MY_TOKEN", "MY_SECRET"]));
+  });
+
+  it("adds warnings for suspicious values", () => {
+    const base64Like =
+      "YWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYWFhYQ==";
+    const result = sanitizeEnvVars({
+      USER: "alice",
+      SAFE_TEXT: base64Like,
+      NULL: "a\0b",
+    });
+
+    expect(result.allowed).toEqual({ USER: "alice", SAFE_TEXT: base64Like });
+    expect(result.blocked).toContain("NULL");
+    expect(result.warnings).toContain("SAFE_TEXT: Value looks like base64-encoded credential data");
+  });
+
+  it("supports strict mode with explicit allowlist", () => {
+    const result = sanitizeEnvVars(
+      {
+        NODE_ENV: "test",
+        FOO: "bar",
+      },
+      { strictMode: true },
+    );
+
+    expect(result.allowed).toEqual({ NODE_ENV: "test" });
+    expect(result.blocked).toEqual(["FOO"]);
+  });
+});
diff --git a/src/agents/sandbox/sanitize-env-vars.ts b/src/agents/sandbox/sanitize-env-vars.ts
new file mode 100644
index 000000000..62bd4a299
--- /dev/null
+++ b/src/agents/sandbox/sanitize-env-vars.ts
@@ -0,0 +1,106 @@
+const BLOCKED_ENV_VAR_PATTERNS: ReadonlyArray<RegExp> = [
+  /^ANTHROPIC_API_KEY$/i,
+  /^OPENAI_API_KEY$/i,
+  /^GEMINI_API_KEY$/i,
+  /^OPENROUTER_API_KEY$/i,
+  /^MINIMAX_API_KEY$/i,
+  /^ELEVENLABS_API_KEY$/i,
+  /^SYNTHETIC_API_KEY$/i,
+  /^TELEGRAM_BOT_TOKEN$/i,
+  /^DISCORD_BOT_TOKEN$/i,
+  /^SLACK_(BOT|APP)_TOKEN$/i,
+  /^LINE_CHANNEL_SECRET$/i,
+  /^LINE_CHANNEL_ACCESS_TOKEN$/i,
+  /^OPENCLAW_GATEWAY_(TOKEN|PASSWORD)$/i,
+  /^AWS_(SECRET_ACCESS_KEY|SECRET_KEY|SESSION_TOKEN)$/i,
+  /^(GH|GITHUB)_TOKEN$/i,
+  /^(AZURE|AZURE_OPENAI|COHERE|AI_GATEWAY|OPENROUTER)_API_KEY$/i,
+  /_?(API_KEY|TOKEN|PASSWORD|PRIVATE_KEY|SECRET)$/i,
+];
+
+const ALLOWED_ENV_VAR_PATTERNS: ReadonlyArray<RegExp> = [
+  /^LANG$/,
+  /^LC_.*$/i,
+  /^PATH$/i,
+  /^HOME$/i,
+  /^USER$/i,
+  /^SHELL$/i,
+  /^TERM$/i,
+  /^TZ$/i,
+  /^NODE_ENV$/i,
+];
+
+export type EnvVarSanitizationResult = {
+  allowed: Record<string, string>;
+  blocked: string[];
+  warnings: string[];
+};
+
+export type EnvSanitizationOptions = {
+  strictMode?: boolean;
+  customBlockedPatterns?: ReadonlyArray<RegExp>;
+  customAllowedPatterns?: ReadonlyArray<RegExp>;
+};
+
+function validateEnvVarValue(value: string): string | undefined {
+  if (value.includes("\0")) {
+    return "Contains null bytes";
+  }
+  if (value.length > 32768) {
+    return "Value exceeds maximum length";
+  }
+  if (/^[A-Za-z0-9+/=]{100,}$/.test(value)) {
+    return "Value looks like base64-encoded credential data";
+  }
+  return undefined;
+}
+
+function matchesAnyPattern(value: string, patterns: readonly RegExp[]): boolean {
+  return patterns.some((pattern) => pattern.test(value));
+}
+
+export function sanitizeEnvVars(
+  envVars: Record<string, string>,
+  options: EnvSanitizationOptions = {},
+): EnvVarSanitizationResult {
+  const allowed: Record<string, string> = {};
+  const blocked: string[] = [];
+  const warnings: string[] = [];
+
+  const blockedPatterns = [...BLOCKED_ENV_VAR_PATTERNS, ...(options.customBlockedPatterns ?? [])];
+  const allowedPatterns = [...ALLOWED_ENV_VAR_PATTERNS, ...(options.customAllowedPatterns ?? [])];
+
+  for (const [rawKey, value] of Object.entries(envVars)) {
+    const key = rawKey.trim();
+    if (!key) {
+      continue;
+    }
+
+    if (matchesAnyPattern(key, blockedPatterns)) {
+      blocked.push(key);
+      continue;
+    }
+
+    if (options.strictMode && !matchesAnyPattern(key, allowedPatterns)) {
+      blocked.push(key);
+      continue;
+    }
+
+    const warning = validateEnvVarValue(value);
+    if (warning) {
+      warnings.push(`${key}: ${warning}`);
+    }
+
+    allowed[key] = value;
+  }
+
+  return { allowed, blocked, warnings };
+}
+
+export function getBlockedPatterns(): string[] {
+  return BLOCKED_ENV_VAR_PATTERNS.map((pattern) => pattern.source);
+}
+
+export function getAllowedPatterns(): string[] {
+  return ALLOWED_ENV_VAR_PATTERNS.map((pattern) => pattern.source);
+}