fix(security): harden shell env fallback

CHANGELOG.md

@@ -36,6 +36,7 @@ Docs: https://docs.openclaw.ai
 
 ### Fixes
 
+- Security/Shell env: validate login-shell executable paths for shell-env fallback (`/etc/shells` + trusted prefixes) and block `SHELL` in dangerous env override policy paths so untrusted shell-path injection falls back safely to `/bin/sh`. Thanks @athuljayaram for reporting.
 - Chat/Usage/TUI: strip synthetic inbound metadata blocks (including `Conversation info` and trailing `Untrusted context` channel metadata wrappers) from displayed conversation history so internal prompt context no longer leaks into user-visible logs.
 - Security/Exec: in non-default setups that manually add `sort` to `tools.exec.safeBins`, block `sort --compress-program` so allowlist-mode safe-bin checks cannot bypass approval. Thanks @tdjackey for reporting.
 - Security/Discord: add `openclaw security audit` warnings for name/tag-based Discord allowlist entries (DM allowlists, guild/channel `users`, and pairing-store entries), highlighting slug-collision risk while keeping name-based matching supported, and canonicalize resolved Discord allowlist names to IDs at runtime without rewriting config files. Thanks @tdjackey for reporting.

apps/macos/Sources/OpenClaw/HostEnvSanitizer.swift

@@ -14,6 +14,7 @@ enum HostEnvSanitizer {
         "RUBYOPT",
         "BASH_ENV",
         "ENV",
+        "SHELL",
         "GCONV_PATH",
         "IFS",
         "SSLKEYLOGFILE",

src/agents/skills.e2e.test.ts

@@ -360,7 +360,7 @@ describe("applySkillEnvOverrides", () => {
       dir: skillDir,
       name: "dangerous-env-skill",
       description: "Needs env",
-      metadata: '{"openclaw":{"requires":{"env":["BASH_ENV"]}}}',
+      metadata: '{"openclaw":{"requires":{"env":["BASH_ENV","SHELL"]}}}',
     });
 
     const entries = loadWorkspaceSkillEntries(workspaceDir, {
@@ -368,7 +368,9 @@ describe("applySkillEnvOverrides", () => {
     });
 
     const originalBashEnv = process.env.BASH_ENV;
+    const originalShell = process.env.SHELL;
     delete process.env.BASH_ENV;
+    delete process.env.SHELL;
 
     const restore = applySkillEnvOverrides({
       skills: entries,
@@ -378,6 +380,7 @@ describe("applySkillEnvOverrides", () => {
             "dangerous-env-skill": {
               env: {
                 BASH_ENV: "/tmp/pwn.sh",
+                SHELL: "/tmp/evil-shell",
               },
             },
           },
@@ -387,6 +390,7 @@ describe("applySkillEnvOverrides", () => {
 
     try {
       expect(process.env.BASH_ENV).toBeUndefined();
+      expect(process.env.SHELL).toBeUndefined();
     } finally {
       restore();
       if (originalBashEnv === undefined) {
@@ -394,6 +398,11 @@ describe("applySkillEnvOverrides", () => {
       } else {
         expect(process.env.BASH_ENV).toBe(originalBashEnv);
       }
+      if (originalShell === undefined) {
+        expect(process.env.SHELL).toBeUndefined();
+      } else {
+        expect(process.env.SHELL).toBe(originalShell);
+      }
     }
   });
 

src/config/config.env-vars.test.ts

@@ -30,18 +30,29 @@ describe("config env vars", () => {
   });
 
   it("blocks dangerous startup env vars from config env", async () => {
-    await withEnvOverride({ BASH_ENV: undefined, OPENROUTER_API_KEY: undefined }, async () => {
-      const config = {
-        env: { vars: { BASH_ENV: "/tmp/pwn.sh", OPENROUTER_API_KEY: "config-key" } },
-      };
-      const entries = collectConfigRuntimeEnvVars(config as OpenClawConfig);
-      expect(entries.BASH_ENV).toBeUndefined();
-      expect(entries.OPENROUTER_API_KEY).toBe("config-key");
+    await withEnvOverride(
+      { BASH_ENV: undefined, SHELL: undefined, OPENROUTER_API_KEY: undefined },
+      async () => {
+        const config = {
+          env: {
+            vars: {
+              BASH_ENV: "/tmp/pwn.sh",
+              SHELL: "/tmp/evil-shell",
+              OPENROUTER_API_KEY: "config-key",
+            },
+          },
+        };
+        const entries = collectConfigRuntimeEnvVars(config as OpenClawConfig);
+        expect(entries.BASH_ENV).toBeUndefined();
+        expect(entries.SHELL).toBeUndefined();
+        expect(entries.OPENROUTER_API_KEY).toBe("config-key");
 
-      applyConfigEnvVars(config as OpenClawConfig);
-      expect(process.env.BASH_ENV).toBeUndefined();
-      expect(process.env.OPENROUTER_API_KEY).toBe("config-key");
-    });
+        applyConfigEnvVars(config as OpenClawConfig);
+        expect(process.env.BASH_ENV).toBeUndefined();
+        expect(process.env.SHELL).toBeUndefined();
+        expect(process.env.OPENROUTER_API_KEY).toBe("config-key");
+      },
+    );
   });
 
   it("drops non-portable env keys from config env", async () => {

src/infra/host-env-security-policy.json

@@ -10,6 +10,7 @@
     "RUBYOPT",
     "BASH_ENV",
     "ENV",
+    "SHELL",
     "GCONV_PATH",
     "IFS",
     "SSLKEYLOGFILE"

src/infra/host-env-security.test.ts

@@ -9,6 +9,7 @@ describe("isDangerousHostEnvVarName", () => {
   it("matches dangerous keys and prefixes case-insensitively", () => {
     expect(isDangerousHostEnvVarName("BASH_ENV")).toBe(true);
     expect(isDangerousHostEnvVarName("bash_env")).toBe(true);
+    expect(isDangerousHostEnvVarName("SHELL")).toBe(true);
     expect(isDangerousHostEnvVarName("DYLD_INSERT_LIBRARIES")).toBe(true);
     expect(isDangerousHostEnvVarName("ld_preload")).toBe(true);
     expect(isDangerousHostEnvVarName("BASH_FUNC_echo%%")).toBe(true);

src/infra/shell-env.test.ts

@@ -121,6 +121,38 @@ describe("shell env fallback", () => {
     expect(exec).toHaveBeenCalledOnce();
   });
 
+  it("falls back to /bin/sh when SHELL is non-absolute", () => {
+    const env: NodeJS.ProcessEnv = { SHELL: "zsh" };
+    const exec = vi.fn(() => Buffer.from("OPENAI_API_KEY=from-shell\0"));
+
+    const res = loadShellEnvFallback({
+      enabled: true,
+      env,
+      expectedKeys: ["OPENAI_API_KEY"],
+      exec: exec as unknown as Parameters<typeof loadShellEnvFallback>[0]["exec"],
+    });
+
+    expect(res.ok).toBe(true);
+    expect(exec).toHaveBeenCalledTimes(1);
+    expect(exec).toHaveBeenCalledWith("/bin/sh", ["-l", "-c", "env -0"], expect.any(Object));
+  });
+
+  it("falls back to /bin/sh when SHELL points to an untrusted path", () => {
+    const env: NodeJS.ProcessEnv = { SHELL: "/tmp/evil-shell" };
+    const exec = vi.fn(() => Buffer.from("OPENAI_API_KEY=from-shell\0"));
+
+    const res = loadShellEnvFallback({
+      enabled: true,
+      env,
+      expectedKeys: ["OPENAI_API_KEY"],
+      exec: exec as unknown as Parameters<typeof loadShellEnvFallback>[0]["exec"],
+    });
+
+    expect(res.ok).toBe(true);
+    expect(exec).toHaveBeenCalledTimes(1);
+    expect(exec).toHaveBeenCalledWith("/bin/sh", ["-l", "-c", "env -0"], expect.any(Object));
+  });
+
   it("returns null without invoking shell on win32", () => {
     resetShellPathCacheForTests();
     const exec = vi.fn(() => Buffer.from("PATH=/usr/local/bin:/usr/bin\0HOME=/tmp\0"));

src/infra/shell-env.ts

@@ -1,10 +1,21 @@
 import { execFileSync } from "node:child_process";
+import fs from "node:fs";
+import path from "node:path";
 import { isTruthyEnvValue } from "./env.js";
 
 const DEFAULT_TIMEOUT_MS = 15_000;
 const DEFAULT_MAX_BUFFER_BYTES = 2 * 1024 * 1024;
+const DEFAULT_SHELL = "/bin/sh";
+const TRUSTED_SHELL_PREFIXES = [
+  "/bin/",
+  "/usr/bin/",
+  "/usr/local/bin/",
+  "/opt/homebrew/bin/",
+  "/run/current-system/sw/bin/",
+];
 let lastAppliedKeys: string[] = [];
 let cachedShellPath: string | null | undefined;
+let cachedEtcShells: Set<string> | null | undefined;
 
 function resolveTimeoutMs(timeoutMs: number | undefined): number {
   if (typeof timeoutMs !== "number" || !Number.isFinite(timeoutMs)) {
@@ -13,9 +24,57 @@ function resolveTimeoutMs(timeoutMs: number | undefined): number {
   return Math.max(0, timeoutMs);
 }
 
+function readEtcShells(): Set<string> | null {
+  if (cachedEtcShells !== undefined) {
+    return cachedEtcShells;
+  }
+  try {
+    const raw = fs.readFileSync("/etc/shells", "utf8");
+    const entries = raw
+      .split(/\r?\n/)
+      .map((line) => line.trim())
+      .filter((line) => line.length > 0 && !line.startsWith("#") && path.isAbsolute(line));
+    cachedEtcShells = new Set(entries);
+  } catch {
+    cachedEtcShells = null;
+  }
+  return cachedEtcShells;
+}
+
+function isTrustedShellPath(shell: string): boolean {
+  if (!path.isAbsolute(shell)) {
+    return false;
+  }
+  const normalized = path.normalize(shell);
+  if (normalized !== shell) {
+    return false;
+  }
+
+  // Primary trust anchor: shell registered in /etc/shells.
+  const registeredShells = readEtcShells();
+  if (registeredShells?.has(shell)) {
+    return true;
+  }
+
+  // Fallback for environments where /etc/shells is incomplete/unavailable.
+  if (!TRUSTED_SHELL_PREFIXES.some((prefix) => shell.startsWith(prefix))) {
+    return false;
+  }
+
+  try {
+    fs.accessSync(shell, fs.constants.X_OK);
+    return true;
+  } catch {
+    return false;
+  }
+}
+
 function resolveShell(env: NodeJS.ProcessEnv): string {
   const shell = env.SHELL?.trim();
-  return shell && shell.length > 0 ? shell : "/bin/sh";
+  if (shell && isTrustedShellPath(shell)) {
+    return shell;
+  }
+  return DEFAULT_SHELL;
 }
 
 function execLoginShellEnvZero(params: {
@@ -171,6 +230,7 @@ export function getShellPathFromLoginShell(opts: {
 
 export function resetShellPathCacheForTests(): void {
   cachedShellPath = undefined;
+  cachedEtcShells = undefined;
 }
 
 export function getShellEnvAppliedKeys(): string[] {