Release v1.3.1: OpSec Patch (Dynamic Fat Frame Entropy)

- Implemented entropy-based pseudo-randomizer in snd_syscall_find_spoof_scan to prevent deterministic telemetry.
- Randomized Fat Frame selection using the SSN hash, a static counter, and ASLR-dependent module/stack addresses.
- Hardened spoof scanner to reject frames using Frame Registers (UWOP_SET_FPREG) to prevent RtlVirtualUnwind crashes.
- Added strict bounds checking to cap Fat Frame sizes at 240 bytes, preventing MASM local stack corruption.Release v1.3.0: Stack Spoofing & Dynamic Fat Frame.

CHANGELOG.md

@@ -6,6 +6,16 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
 
 ---
 
+## [1.3.1] - 2026-07-07
+
+OpSec Patch release addressing deterministic telemetry in stack spoofing.
+
+### Security & OpSec
+- **Fat Frame Entropy:** Implemented a pseudo-randomizer in `snd_syscall_find_spoof_scan` to prevent deterministic stack spoofing telemetry. The engine now uses the target function's SSN hash, a static counter, and the ASLR-dependent memory addresses of the `ntdll` base and the entry struct to randomize the selection of Fat Frames. This ensures payloads do not spoof the exact same `kernel32.dll` function on every execution, shifting the stack trace dynamically.
+- **Fat Frame Hardening:** Added strict bounds checking to the spoof scanner. It now rejects functions that use a Frame Register (which could break `RtlVirtualUnwind` offset calculations) and caps the selected `frame_size` to a maximum of 240 bytes to ensure it cannot overflow the pre-allocated local stack space inside the MASM stub.
+
+---
+
 ## [1.3.0] - 2026-07-06
 
 Fourth major release. The framework introduces Call Stack Spoofing to defeat EDR virtual unwinding telemetry.

docs/domains/primitives/syscalls/engines.md

@@ -142,9 +142,10 @@ To prevent frame desynchronization during stack unwinding (where the EDR's `RtlV
 1. Resolve the natively loaded `kernel32.dll` via PEB.
 2. Manually parse the **Exception Directory** (`.pdata`) of `kernel32.dll` (avoiding native APIs like `RtlLookupFunctionEntry` for stealth).
 3. Iterate through `RUNTIME_FUNCTION` entries and parse their `UNWIND_INFO` structures to calculate the total stack space allocated by each function.
-4. Find a function that allocates at least **120 bytes** (a "Fat Frame"). This ensures the legitimate function's shadow space is large enough to encapsulate our spoofed JMP-trampoline and its arguments.
+4. Find a function that allocates at least **120 bytes** and at most **240 bytes** (a capped "Fat Frame"). This ensures the legitimate function's shadow space is large enough to encapsulate our spoofed JMP-trampoline and its arguments without risking stack overflow.
-5. Scan the body of the Fat Frame function for a `0xC3` (`RET`) instruction.
+5. **Entropy Randomization:** To avoid creating a deterministic telemetry pattern (where every syscall spoofs the exact same function), the scanner uses an internal pseudo-randomizer seeded by the target function's hash, a static counter, and the memory addresses of the `ntdll` base and the entry struct. This guarantees it will skip a randomized number of valid Fat Frames before settling on one.
-6. Populate `entry->pSpoofAddr` with the gadget address and `entry->dwSpoofFrameSize` with the required stack offset.
+6. Scan the body of the chosen Fat Frame function for a `0xC3` (`RET`) instruction.
+7. Populate `entry->pSpoofAddr` with the gadget address and `entry->dwSpoofFrameSize` with the required stack offset.
 
 ### Algorithm (x86)
 

src/primitives/execution/syscalls/spoof_scan.c

@@ -33,6 +33,15 @@ snd_status_t snd_syscall_find_spoof_scan(snd_syscall_entry_t *entry) {
         PRUNTIME_FUNCTION pdata       = (PRUNTIME_FUNCTION)((ULONG_PTR)kernel32 + pdata_rva);
         DWORD             pdata_count = pdata_size / sizeof(RUNTIME_FUNCTION);
 
+        // Simple randomizer using a static counter + hash + memory addresses for entropy
+        static ULONG call_count = 0;
+        ULONG        entropy    = (ULONG)((ULONG_PTR)kernel32 & 0xFFFFFFFF) ^ (ULONG)((ULONG_PTR)entry & 0xFFFFFFFF);
+        ULONG        skip_count = (entry->dwHash + ++call_count + entropy) % 15; // Skip up to 14 fat frames
+        ULONG        current_fat_frames = 0;
+
+        PVOID fallback_gadget     = NULL;
+        DWORD fallback_frame_size = 0;
+
         for (DWORD i = 0; i < pdata_count; i++) {
             PRUNTIME_FUNCTION func = &pdata[i];
 
@@ -48,6 +57,11 @@ snd_status_t snd_syscall_find_spoof_scan(snd_syscall_entry_t *entry) {
                 continue;
             }
 
+            BYTE frameReg = unwind_info[3] & 0x0F;
+            if (frameReg != 0) {
+                continue; // Reject functions that use a frame pointer to prevent RtlVirtualUnwind desync
+            }
+
             BYTE  countOfCodes = unwind_info[2];
             PBYTE codes        = unwind_info + 4;
 
@@ -99,7 +113,7 @@ snd_status_t snd_syscall_find_spoof_scan(snd_syscall_entry_t *entry) {
                 }
             }
 
-            if (frame_size >= 120) {
+            if (frame_size >= 120 && frame_size <= 240) {
                 PBYTE func_body = (PBYTE)((ULONG_PTR)kernel32 + func->BeginAddress);
                 DWORD func_size = func->EndAddress - func->BeginAddress;
 
@@ -111,10 +125,26 @@ snd_status_t snd_syscall_find_spoof_scan(snd_syscall_entry_t *entry) {
                     }
                 }
 
-                if (gadget)
+                if (gadget) {
+                    if (!fallback_gadget) {
+                        fallback_gadget     = gadget;
+                        fallback_frame_size = frame_size;
+                    }
+
+                    if (current_fat_frames < skip_count) {
+                        current_fat_frames++;
+                        gadget = NULL; // Keep searching for the next one
+                        continue;
+                    }
                     break;
+                }
             }
         }
+
+        if (!gadget && fallback_gadget) {
+            gadget                  = fallback_gadget;
+            entry->dwSpoofFrameSize = fallback_frame_size;
+        }
     }
 #else
     FARPROC exec_addr = NULL;