Portaloo

hackthebox

Task: 64-bit PIE binary with heap UAF, mprotect making heap RWX, and stack buffer overflow with canary. Solution: Write shellcode to RWX heap, leak heap address via tcache safe-linking UAF, leak canary via null byte overwrite, stack smash to jump to shellcode.

pie heap shellcode tcache safe-linking pwn use-after-free stack-overflow rwx-heap mprotect canary-leak glibc-2.35

canary_null_byte_overwrite_leakmprotect_rwx_abuseshellcode_on_heapstack_bof_ret2shellcodetcache_safe_linking_bypassuaf_heap_leak

$ ls tags/ techniques/

pie heap shellcode tcache safe-linking pwn use-after-free stack-overflow rwx-heap mprotect canary-leak glibc-2.35

canary_null_byte_overwrite_leakmprotect_rwx_abuseshellcode_on_heapstack_bof_ret2shellcodetcache_safe_linking_bypassuaf_heap_leak

$ cat /etc/rate-limit

Rate limit reached (20 reads/hour per IP). Showing preview only — full content returns at the next hour roll-over.

Portaloo — HackTheBox

Description

"Portals... A gateway to other dimensions, where chaos meets creativity and the void greets you."

64-bit ELF PIE binary with full protections (Full RELRO, NX, Canary, PIE). Custom glibc 2.35 (Ubuntu GLIBC 2.35-0ubuntu3.8) provided. Remote target: 154.57.164.78:32357.

The binary is a portal management system with 5 menu options:

Create Portal — malloc(0x20), stores pointer in slots[0] or slots[1]. On first allocation, calls mprotect() on the heap page with flags PROT_READ|PROT_WRITE|PROT_EXEC (7) — makes the heap RWX.
Destroy Portal — free(slots[n]), but does NOT NULL the pointer (UAF).
Upgrade Portal — read(0, slots[n], 0x15) — writes 21 bytes to the portal.
Peek into the Void — printf("Coordinate: %d ---- Data: %.*s", 0x15, i, slots[i]) — reads portal data.
Step into the Portal — stack buffer of 0x48 bytes. First read() for 0x50 bytes (8-byte overflow past buffer into canary). Second read() for 0x68 bytes (0x20-byte overflow — overwrites canary, saved rbp, return address). After this function, main calls exit(0).

Global Variables

slots[2] at address 0x4060 — array of 2 heap pointers
mprotect_called at address 0x4050 — flag ensuring mprotect is called only once

Protections

Protection	Status
PIE	✅ Enabled
NX	✅ Enabled (but heap is made RWX via mprotect!)
Canary	✅ Enabled
RELRO	Full

Analysis

Vulnerability 1: RWX Heap (mprotect abuse)

In create_portal(), the first allocation triggers:

page_aligned = slots[n] & ~(page_size - 1);
mprotect(page_aligned, page_size, PROT_READ|PROT_WRITE|PROT_EXEC);

This makes the entire heap page executable — perfect for shellcode.

Vulnerability 2: Use-After-Free (UAF)

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