From bd7b11f0242ddcb9f96010c784cd548d58ce65d2 Mon Sep 17 00:00:00 2001
From: "google-labs-jules[bot]"
 <161369871+google-labs-jules[bot]@users.noreply.github.com>
Date: Fri, 12 Jun 2026 07:39:53 +0000
Subject: [PATCH] =?UTF-8?q?=F0=9F=9B=A1=EF=B8=8F=20Sentinel:=20[CRITICAL/H?=
 =?UTF-8?q?IGH]=20Fix=20TOCTOU=20vulnerability=20in=20file=20creation?=
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Co-authored-by: acebytes <2820910+acebytes@users.noreply.github.com>
---
 .jules/sentinel.md                          |  5 +++++
 Sources/Cacheout/Cleaner/CacheCleaner.swift | 24 +++++++++++++++------
 2 files changed, 22 insertions(+), 7 deletions(-)

diff --git a/.jules/sentinel.md b/.jules/sentinel.md
index fd58571..38ef279 100644
--- a/.jules/sentinel.md
+++ b/.jules/sentinel.md
@@ -31,3 +31,8 @@
 **Vulnerability:** External shell command executed in `listLocalSnapshots()` triggered a deadlock when `tmutil` output exceeded 64KB, because stdout and stderr were read synchronously inside the process termination handler.
 **Learning:** In Swift, reading from a process pipe synchronously inside a `terminationHandler` can result in a permanent deadlock if the child blocks writing to a full pipe, preventing it from exiting.
 **Prevention:** Asynchronously drain pipes continuously while the process is running using background queues.
+
+## 2026-05-02 - Fix TOCTOU vulnerability in file creation
+**Vulnerability:** High-level Swift file APIs (`FileHandle(forWritingTo:)`, `String.write(to:atomically:)`) follow symlinks by default, leading to Time-of-Check to Time-of-Use (TOCTOU) symlink vulnerabilities.
+**Learning:** High-level APIs are inherently insecure when writing to paths that could be tampered with. The vulnerability can be exploited to overwrite arbitrary files if an attacker replaces a file or directory with a symlink before the application writes to it.
+**Prevention:** Use POSIX `open(2)` with flags like `O_CREAT | O_WRONLY | O_APPEND | O_NOFOLLOW | O_CLOEXEC` to explicitly refuse following symlinks, securely create the file, and then wrap the resulting file descriptor in a `FileHandle`.
diff --git a/Sources/Cacheout/Cleaner/CacheCleaner.swift b/Sources/Cacheout/Cleaner/CacheCleaner.swift
index 2111e6a..ebd352a 100644
--- a/Sources/Cacheout/Cleaner/CacheCleaner.swift
+++ b/Sources/Cacheout/Cleaner/CacheCleaner.swift
@@ -34,6 +34,7 @@
 
 import Foundation
 import AppKit
+import Darwin
 
 actor CacheCleaner {
     private let fileManager = FileManager.default
@@ -255,18 +256,27 @@ actor CacheCleaner {
     private func logCleanup(category: String, bytesFreed: Int64) {
         let logDir = FileManager.default.homeDirectoryForCurrentUser
             .appendingPathComponent(".cacheout")
-        try? FileManager.default.createDirectory(at: logDir, withIntermediateDirectories: true)
+        try? FileManager.default.createDirectory(at: logDir, withIntermediateDirectories: true, attributes: [.posixPermissions: 0o700])
 
         let logFile = logDir.appendingPathComponent("cleanup.log")
         let size = ByteCountFormatter.sharedFile.string(fromByteCount: bytesFreed)
         let entry = "[\(ISO8601DateFormatter.shared.string(from: Date()))] Cleaned \(category): \(size)\n"
 
-        if let handle = try? FileHandle(forWritingTo: logFile) {
-            handle.seekToEndOfFile()
-            handle.write(entry.data(using: .utf8) ?? Data())
-            handle.closeFile()
-        } else {
-            try? entry.write(to: logFile, atomically: true, encoding: .utf8)
+        _ = logFile.withUnsafeFileSystemRepresentation { pathPtr -> Int32 in
+            guard let pathPtr = pathPtr else { return -1 }
+            let fd = open(pathPtr, O_CREAT | O_WRONLY | O_APPEND | O_NOFOLLOW | O_CLOEXEC, 0o600)
+            if fd != -1 {
+                let handle = FileHandle(fileDescriptor: fd, closeOnDealloc: true)
+                let data = entry.data(using: .utf8) ?? Data()
+                if #available(macOS 10.15.4, *) {
+                    try? handle.write(contentsOf: data)
+                    try? handle.close()
+                } else {
+                    handle.write(data)
+                    handle.closeFile()
+                }
+            }
+            return fd
         }
     }
 }