The SQL Server Crypto Detour – SpecterOps

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SQL Server is a critical component in many enterprise environments, and understanding its cryptographic mechanisms is essential for both offensive and defensive security professionals. SpecterOps’ research on The SQL Server Crypto Detour dives deep into how SQL Server handles encryption and how attackers can manipulate these mechanisms.

You Should Know:

1. SQL Server Encryption Mechanisms

SQL Server uses cryptographic functions for:

  • Transparent Data Encryption (TDE)
  • Column-level encryption
  • SSL/TLS for network encryption

Attackers may intercept or manipulate these functions using API hooking or DLL injection.

2. Detouring Crypto Functions

SpecterOps highlights how attackers can bypass SQL Server’s native encryption by detouring cryptographic APIs such as:
– `CryptEncrypt` / `CryptDecrypt` (from Advapi32.dll)
– `BCryptEncrypt` / `BCryptDecrypt` (from Bcrypt.dll)

Example: Hooking `CryptEncrypt` in C++

include <windows.h>
include <detours.h>

// Original function pointer
BOOL (WINAPI TrueCryptEncrypt)(HCRYPTKEY, HCRYPTHASH, BOOL, DWORD, BYTE, DWORD, DWORD) = CryptEncrypt;

// Hooked function
BOOL WINAPI HookedCryptEncrypt(HCRYPTKEY hKey, HCRYPTHASH hHash, BOOL Final, DWORD dwFlags, BYTE pbData, DWORD pdwDataLen, DWORD dwBufLen) {
printf("[+] CryptEncrypt called - data can be intercepted or modified!\n");
return TrueCryptEncrypt(hKey, hHash, Final, dwFlags, pbData, pdwDataLen, dwBufLen);
}

int main() {
DetourTransactionBegin();
DetourUpdateThread(GetCurrentThread());
DetourAttach(&(PVOID&)TrueCryptEncrypt, HookedCryptEncrypt);
DetourTransactionCommit();

// Test SQL Server encryption operations here
return 0;
}

3. Defensive Measures

To detect such attacks:

  • Monitor for unusual DLL injections:
    Get-Process | Where-Object { $_.Modules.ModuleName -match "malicious.dll" }
  • Enable Sysmon logging for cryptographic API calls:
    <RuleGroup name="Crypto API Monitoring">
<ProcessCreate onmatch="include">
<Image condition="contains">sqlservr.exe</Image>
</ProcessCreate>
<FileCreate onmatch="include">
<TargetFilename condition="contains">bcrypt.dll</TargetFilename>
</FileCreate>
</RuleGroup>
  • Use PowerShell to check loaded modules in SQL Server:
    Get-Process -Name "sqlservr" | Select-Object -ExpandProperty Modules | Format-Table -AutoSize

4. Linux Equivalent: OpenSSL Hooking (LD_PRELOAD Attack)

On Linux, attackers may hook OpenSSL functions:

include <dlfcn.h>
include <openssl/ssl.h>

// Original function
int (original_SSL_write)(SSL ssl, const void buf, int num) = NULL;

// Hooked function
int SSL_write(SSL ssl, const void buf, int num) {
original_SSL_write = dlsym(RTLD_NEXT, "SSL_write");
printf("[+] Intercepted SSL_write: Data can be logged or modified!\n");
return original_SSL_write(ssl, buf, num);
}

Compile with:

gcc -shared -fPIC -o libmalicious.so hook_openssl.c -ldl

Inject using:

LD_PRELOAD=./libmalicious.so sqlcmd -S server -U user -P password

What Undercode Say

SQL Server’s cryptographic functions are a prime target for attackers, especially in advanced persistent threat (APT) scenarios. SpecterOps’ research underscores the importance of runtime protection, API call monitoring, and memory integrity checks. Defenders should:
– Log cryptographic API calls via ETW (Event Tracing for Windows).
– Restrict DLL loading in SQL Server with:

Set-ProcessMitigation -Name sqlservr.exe -Disable DynamicCode

– Use YARA rules to detect malicious hooks:

rule detect_crypto_hooks {
strings:
$hook = { 68 ?? ?? ?? ?? E9 ?? ?? ?? ?? }
condition:
$hook in (0..1000)
}

– Deploy EDR solutions that monitor `sqlservr.exe` for abnormal behavior.

For Linux-based SQL alternatives (e.g., PostgreSQL), focus on:

strace -e trace=open,read,write -p $(pgrep postgres)

Expected Output:

  • Detected hooked `CryptEncrypt` calls in SQL Server.
  • Alert on unauthorized DLLs loaded into sqlservr.exe.
  • Blocked `LD_PRELOAD` attacks on Linux SQL services.

Prediction

As SQL Server evolves, attackers will shift to kernel-level crypto hooks (e.g., via rootkits). Defenders must adopt hypervisor-protected code integrity (HVCI) and eBPF-based Linux monitoring to stay ahead.

Reference: The SQL Server Crypto Detour – SpecterOps

References:

Reported By: Florian Hansemann – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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