fix(macos): harden exec approval socket auth

CHANGELOG.md

@@ -112,6 +112,7 @@ Docs: https://docs.openclaw.ai
 - Control UI/overview: keep the language dropdown aligned with the persisted locale during dashboard startup so refreshing the page does not fall back to English before locale hydration completes. (#48019) Thanks @git-jxj.
 - Agents/compaction: rerun transcript repair after `session.compact()` so orphaned `tool_result` blocks cannot survive compaction and break later Anthropic requests. (#16095) thanks @claw-sylphx.
 - Agents/compaction: trigger overflow recovery from the tool-result guard once post-compaction context still exceeds the safe threshold, so long tool loops compact before the next model call hard-fails. (#29371) thanks @keshav55.
+- macOS/exec approvals: harden exec-host request HMAC verification to use a timing-safe compare and keep malformed or truncated signatures fail-closed in focused IPC auth coverage.
 
 ## 2026.3.13
 

apps/macos/Sources/OpenClaw/ExecApprovalsSocket.swift

@@ -89,6 +89,20 @@ private func readLineFromHandle(_ handle: FileHandle, maxBytes: Int) throws -> S
     return String(data: lineData, encoding: .utf8)
 }
 
+func timingSafeHexStringEquals(_ lhs: String, _ rhs: String) -> Bool {
+    let lhsBytes = Array(lhs.utf8)
+    let rhsBytes = Array(rhs.utf8)
+    guard lhsBytes.count == rhsBytes.count else {
+        return false
+    }
+
+    var diff: UInt8 = 0
+    for index in lhsBytes.indices {
+        diff |= lhsBytes[index] ^ rhsBytes[index]
+    }
+    return diff == 0
+}
+
 enum ExecApprovalsSocketClient {
     private struct TimeoutError: LocalizedError {
         var message: String
@@ -854,7 +868,7 @@ private final class ExecApprovalsSocketServer: @unchecked Sendable {
                 error: ExecHostError(code: "INVALID_REQUEST", message: "expired request", reason: "ttl"))
         }
         let expected = self.hmacHex(nonce: request.nonce, ts: request.ts, requestJson: request.requestJson)
-        if expected != request.hmac {
+        if !timingSafeHexStringEquals(expected, request.hmac) {
             return ExecHostResponse(
                 type: "exec-res",
                 id: request.id,

apps/macos/Tests/OpenClawIPCTests/ExecApprovalsSocketAuthTests.swift

@@ -0,0 +1,21 @@
+import Testing
+@testable import OpenClaw
+
+struct ExecApprovalsSocketAuthTests {
+    @Test
+    func `timing safe hex compare matches equal strings`() {
+        #expect(timingSafeHexStringEquals(String(repeating: "a", count: 64), String(repeating: "a", count: 64)))
+    }
+
+    @Test
+    func `timing safe hex compare rejects mismatched strings`() {
+        let expected = String(repeating: "a", count: 63) + "b"
+        let provided = String(repeating: "a", count: 63) + "c"
+        #expect(!timingSafeHexStringEquals(expected, provided))
+    }
+
+    @Test
+    func `timing safe hex compare rejects different length strings`() {
+        #expect(!timingSafeHexStringEquals(String(repeating: "a", count: 64), "deadbeef"))
+    }
+}