I. OVERVIEW
For people who do Red Team work or those who handle malware reversing,
forensics. Metadata in Windows PE files probably isn’t new to you.
Attackers will try to remove or tamper with that metadata so the file
looks legitimate or leaves as little trace as possible. Defenders, on the
other hand, will look for such information to track activity and cluster
related malware, or even tie it back to criminal groups.
In this article, I’ll cover Operational Security (OPSEC) techniques for PE
files on Windows. I’ll also release a toolkit to help check the most
common metadata artifacts that both red teams and blue teams often rely
on.
The goal of this piece is to give red-team developers and game developers
one more final checkpoint before deploying their product into the real
world.
Find me on X to get the latest pentest and red team tricks that I've
been researching:
Two Seven One Three (@TwoSevenOneT) / X
II. MAIN SECTION
First, I’d like to introduce the toolset I just developed for OPSEC with
PE files.
The tool is called PE-OopsSec. It consists of several small tools,
each with its own different functions. With this toolkit, I’ll break down
the PE file records that red teams and blue teams need to pay attention
to.
In this article, I’ll focus mainly on PE files generated with Visual
Studio.
1. PE File's Optional Header: Subsystem
The Subsystem field in a PE file's Optional Header tells the
Windows operating system how to run the program. The two main types are
Windows GUI (Graphical User Interface) and
Windows CUI (Console User Interface)
When we run payloads, especially when sharing the same session with the
User, the payloads often need to be compiled with the Subsystem flag in
the header set to ‘GUI’ to ensure the command prompt window is
hidden and doesn’t pop up.
To be even more discreet, we can use the WinMain() function instead of
main(), along with creating some graphic elements (dialog boxes, UI
windows) so that the payload looks exactly like a normal GUI program.
Visual Studio: Project Properties => Linker => System =>
Subsystem
The PECheck tool in the PE-OopsSec suite helps us figure out
what kind of Subsystem our file is running under.
2. PE Header: Debug Symbol
Debug Symbol PE file header occurs when a software developer
accidentally leaves internal debugging information inside a compiled
Windows executable (Portable Executable / PE file).
This happens when a program is compiled in Debug mode instead of
Release mode, or when debug symbols are not stripped before distribution.
Leaving this header intact exposes highly sensitive metadata to reverse
engineers, threat intelligence analysts, or adversaries:
- Reveals Usernames: The PDB path often includes the developer's local username (e.g., C:\Users\john_doe\Documents\SecretProject\...).
- Exposes Internal Infrastructure: It leaks folder hierarchies, drive letters, and internal naming conventions of network shares or build servers.
- Discloses Source Code Structure: It reveals the names of original source files, external libraries used, and project organization.
- Identifies the Threat Actor: In malware analysis, this metadata is frequently used by defenders to attribute attacks to specific groups or individuals based on unique naming patterns and language artifacts.
Visual Studio (C/C++): Go to Project Properties => Linker =>
Debugging => Set Generate Debug Info to No
Continue using the PECheck tool in the PE-OopsSec suite to
inspect the Debug Symbol.
3. Build Flag: /MT NOT /MD or /MTD
While /MT (Static Release) has some OPSEC drawbacks for stealth
payloads, it exists because it provides massive operational benefits for
reliability and deployment speed.
No Missing DLLs: Gets rid of the dreaded “VCRUNTIME140.dll not found” error. Have you ever run into this? The payload works fine on your dev
box, but out in the wild it falls flat.
The /MT Packs everything into a single executable, ensuring it runs
on a fresh Windows install without requiring the Visual C++
Redistributable package
Note: Avoid the D variants (/MTd or /MDd) for production, as
these are for Debug builds and add heavy diagnostic overhead.
Visual Studio: Properties => C/C++ => Code Generation =>
Runtime Library
4. PE Rich Header
The Rich Header is an undocumented block inserted by Microsoft’s
linker (link.exe) between the DOS Stub and the NT Headers. It contains
exact product IDs, build numbers, and execution counts of the compiler
toolchain used to build the program.
When a developer strips or customizes other PE headers to look like a
specific compiler but forgets the Rich Header, they leave a glaring
contradiction.
Malware analysts heavily utilize the rich_signature hash (often generated
via YARA or Python tools) to group and track malware families: Reusing the
exact same build machine and environment to compile distinct payloads for
entirely different operational targets or clients.
Some developers try to mimic other actors or legitimate software by
manually overlaying a fake Rich Header: Pasting a static Rich Header
copied from a legitimate system file into a newly created malware binary
without correcting the "count" entries or matching it with the payload's
actual composition.
Primary mitigation methods:
- Complete Stripping: Overwriting the entire block between the DOS stub and NT headers with null bytes (0x00).
- Alternative Toolchains: Compiling with linkers that do not generate a Rich Header, such as GCC via MinGW or the LLVM Clang toolchain.
- Linker Flags: Passing the undocumented flag /EMITTOOLVERSIONINFO:NO (or equivalent flags depending on the exact MSVC builder variant) during the linking phase to prevent its generation.
Visual Studio: Properties => Linker => Command Line =>
Additional Options
Results from running the PECheck tool in the PE-OopsSec suite.
5. PE OriginalFilename
The OriginalFilename OPSEC mistake occurs when you rename a
Portable Executable (PE) binary on disk to evade detection, but forgets to
modify the embedded VERSIONINFO resource header.
Because the OriginalFilename field remains hardcoded inside the PE
file's metadata, it creates an immediate discrepancy that blue teams,
Endpoint Detection and Response (EDR) agents, and antivirus heuristics
flag as highly suspicious.
6. PE TimeStamp
the PE (Portable Executable) file TimeStamp is a notorious area for
Operational Security (OPSEC) mistakes. Security analysts, threat hunters,
and automated sandboxes heavily scrutinize compilation timestamps to map
out threat actor campaigns and identify anomalies.
The most critical OPSEC mistakes surrounding PE timestamps involve incomplete timestomping, chronologically impossible overlaps, and data correlation failures.
The most common mistake is assuming that a PE file contains only one
timestamp. While developers usually clear or modify the main COFF file
header (IMAGE_FILE_HEADER.TimeDateStamp), the PE format embeds timestamps
in up to six different locations.
When operators attempt to manually fake a timestamp to blend in with
legacy software, they often fail to research the history of their own
toolchains. Ex: Setting a timestamp to 2010 for a binary compiled with
Visual Studio 2022 features or utilizing Visual C++ runtime features that
didn't exist in 2010 creates an impossible pairing.
When deploying a cluster of different tools (e.g., a dropper, a loader,
and a C2 agent), an operator might use a script to generic-stamp all
payloads to an identical fake date (e.g., 0x30000000 / Dec 24, 1995).
Threat hunters search global databases like VirusTotal for exact timestamp
overlaps.
Modern compilers (like Microsoft's
/experimental:deterministic flag) completely remove the epoch time
and instead place a hash of the binary data into the
TimeDateStamp field. This makes the build perfectly reproducible
and prevents tracking actual development time.
Visual Studio:
Configuration Properties => C/C++ => Command Line => Additional
Options => /experimental:deterministic
Configuration Properties => Linker => Command Line => Additional
Options => /BREPRO
7. Resource Section (.RSRC) Language IDs
The IMAGE_RESOURCE_DIRECTORY contains language and sub-language
identifiers (LCIDs) for menus, icons, and version strings.
Even if the malware code is generic, the resource section may default to
the developer's native system language (e.g., Russian, Chinese, Persian),
exposing geographical origins.
8. Import Address Table (IAT): Leaving a "Malicious" Signature
If a custom payload compiles using standard linking (#include <windows.h> followed by standard function calls), the binary explicitly declares
its intentions to the operating system. Security tools leverage this to
evaluate a file's capabilities.
For instance, an executable containing the following block of imports will
instantly score a high-risk malicious verdict on any endpoint:
- kernel32.dll: VirtualAlloc, VirtualProtect, WriteProcessMemory, CreateRemoteThread.
- ntdll.dll: NtMapViewOfSection, NtUnmapViewOfSection.
Even if the payload's shellcode is fully encrypted, the structural
metadata on disk tells the EDR exactly what techniques (like Process
Injection or API Hooking) the file is designed to perform.
You can completely strip dangerous APIs from the compiled IAT by resolving
them dynamically at runtime:
Dynamic API Resolving, API Hashing, Custom PEB Walking,…
9. RTTI (Runtine Type Infomation)
The ultimate RTTI (Runtime Type Information) OPSEC mistake
in PE (Portable Executable) files is leaving compiler-generated RTTI
structures intact during production builds, which leaks the original C++
class hierarchy, exact class names, and inheritance relationships directly
to reverse engineers.
When a developer compiles a C++ project with RTTI enabled (e.g.,
using /GR in MSVC), the compiler embeds descriptive metadata inside the
.rdata section. Tools like IDA Pro, Ghidra use this metadata
to automatically reconstruct the entire application architecture,
completely neutralizing any code obfuscation or stripping efforts.
Visual Studio: Properties -> C/C++ -> Language -> Enable
Run-Time Type Information -> No (/GR-).
10. PE File IMPHASH (Import Hash)
When a PE file is compiled, the linker writes imported functions into the
IAT in the exact sequence they are declared or processed in the
source code.
An operator makes a critical OPSEC mistake by relying solely on:
- Changing the payload's outer hash: Adding junk bytes, changing strings, or modifying resources shifts the SHA256 completely but leaves the IMPHASH 100% identical.
- Automated code obfuscation: Basic packers or crypters that do not mask the import table will still expose a static, unique signature.
If an EDR or threat hunter flags an older version of your tool, they will
create an alert rule for its IMPHASH. The moment your newly compiled
payload touches a disk scanned by an endpoint agent or gets uploaded to
VirusTotal or MalwareBazaar, it fires an immediate match,
blowing the entire operation.
You can check the IMHASH of your PE files using the PEHash tool in
the PE-OopsSec suite. The best way to use this tool is to build a
batch of payload variants and place them all in the same folder — the tool
will scan them and highlight any duplicate information across the files.
11. PE File FUZZY HASH: SSDEEP
SSDEEP uses Context-Triggered Piecewise Hashing (CTPH) to
match data based on structural similarity. This means defender security
systems will instantly flag and cluster the modified binary with known,
documented campaigns.
SSDEEP slices files into dynamic chunks based on content context rather
than static byte intervals. If you only swap out an IP address or a C2
domain string inside a 500KB PE payload, over 99% of the file structure
remains completely identical, yielding an SSDEEP similarity score near
100%.
The SSDEEP algorithm outputs a similarity score between 0 and 100, where 0
means no detected similarity and 100 means the structural layout is nearly
identical.
Note: Threat hunters do not just look at the whole file; they calculate
ImpFuzzy (SSDEEP applied exclusively to the PE Import Address Table). If
an operator alters the entire execution flow but reuses the same Win32
API calls in the same order, the tool catches them anyway.
Adding garbage overlay padding, changing function names, or altering
variable assignments changes the cryptographic hash but fails to alter the
binary's macro layout. Defenders use this flaw to pivot from a single
burned payload to map out an entire developer profile or toolset.
Modern Endpoint Detection and Response (EDR) agents and platforms like
VirusTotal automatically map your "new" payload straight to your old
infrastructure.
If your new payload gets flagged instantly because its SSDEEP matches a
known strain, it burns any fresh, expensive C2 redirectors, domains, and
certificates associated with it.
Reusing the same compiler, boilerplate code templates, or entrypoint
structures generates overlapping fuzzy hashes that allow threat
intelligence agencies to tie an active operation directly to historic
groups.
Checking with the PEHash tool in the PE-OopsSec suite.
12. PE Entropy
Entropy OPSEC mistake occurs when a red teamer, malware developer, or
penetration tester protects their payload using encryption, obfuscation,
or packing, but inadvertently leaves the binary with a
highly elevated Shannon entropy score (typically > 7.2).
Because natural, uncompiled text or standard compiled code clusters around
moderate values (between 4.5 and 6.5), a section approaching the
theoretical maximum of 8.0 acts as an instant beacon for static analysis
engines.
Security tools and Endpoint Detection and Response (EDR) platforms do not
need to decrypt the file to flag it; they simply look at the math and
immediately redirect the suspicious binary to an automated dynamic sandbox
or flag it for quarantine.
Placing encrypted shellcode or payload data directly inside the main
executable code section (.text). Standard code has a predictable,
structured pattern; randomizing it pushes the .text entropy beyond 7.0,
triggering immediate static alerts.
Some techniques to counter this: Padding with Null or Low-Entropy Bytes,
Format-Preserving Encryption, English Text / Code Injection,…
III. CLOSURE
Earlier, I walked through a series of common pitfalls when deploying a
payload into a live environment. Any payload can be reused multiple times
(by changing its encoding, C2 details, encryption, etc.), and just a small
slip-up can blow the lid off your entire system or expose previously
deployed payloads.
Once you trip over those mistakes, your payload might get flagged or
tracked right from the moment you build it, long before you even put it to
use.
The PE-OopsSec suite gives you the basic functions to use it as a final
checkpoint for payloads before pushing them into production. This is
especially handy for builder-style models that churn out payloads in bulk.
For example, you can hook it into a tool or portal that generates
payloads, and it will automatically “sweep” for common OPSEC blunders,
those little errors we often overlook when handling large volumes.
Software and game developers can also borrow some of these concealment
techniques to make their applications or games tougher to analyze or
cheat.
Author of the article:
Two Seven One Three
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