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Screenshot from Check Point Research of a fake Claude Opus download page titled "Download Claude 5 Free - Opus 5 & Opus 4.8 for Windows," with a large orange Download Claude 5 Free button and copy claiming the free AI coding agent for your PC needs no subscription.
Screenshot: Check Point Research, "Tricks from the Past deployed via signed ChatGPT and Claude binaries," Oct. 27, 2026 (fair use). The page is one of the GitHub.io lures used in the Yoba campaign.

Threat Intel

Check Point Says Fake ChatGPT and Claude Desktop Apps on GitHub Sideload Malware Through Signed OpenAI and Anthropic Binaries, Then Fetch Payloads Via a Telegram Image and DNS Over HTTPS

The campaign Check Point Research tracks as Yoba packages malware next to signed OpenAI and Anthropic Setup.exe files in fake GitHub projects, then uses a Telegram channel image as the seed for a DNS-over-HTTPS tasking channel. The final payload seen so far is an XMRig miner routed through Tor, but the loader can fetch any PE or PowerShell stage.

Priya Shah, Threat IntelSingapore7 min read

SINGAPORE - Check Point Research says attackers spent the past two months pushing fake ChatGPT and Claude desktop apps through GitHub repositories and GitHub.io pages so that victims run legitimate, signed OpenAI and Anthropic installers that load a malicious DLL.

The researchers track the campaign as Yoba. The installers place malware next to signed Setup.exe binaries from OpenAI and Anthropic, a classic DLL sideloading pattern. The dropper later persists by copying Windows Media Player's WMPDMC.exe into ProgramData and scheduling it to load a second-stage loader. That loader reads a Telegram channel profile image, derives a domain name from the last 50 bytes of the image, and retrieves an AES-encrypted task over Google's DNS-over-HTTPS API. In the samples Check Point examined, the final payload was XMRig 6.26.0 mining through a Tor SOCKS5 proxy, but the loader can deploy any PE or PowerShell stage the operator signs into DNS.

Fake AI apps on GitHub

Initial access came through malicious GitHub repositories that impersonated AI desktop applications named GPT-5.6 Sol, GPT-6 Astra and Claude Opus. Check Point says the repositories did not fake stars or forks, but still ranked near the top of Google results for those product names, which the researchers attribute to SEO poisoning of titles, descriptions and hosting domains.

Check Point Research attack-chain diagram for the GPT-6 Astra wave of the Yoba campaign, showing ChatGPT SEO poisoning and GitHub releases feeding a signed OpenAI Setup.exe that sideloads a Main Loader, then a Telegram image seed, a DGA domain, DNS over HTTPS tasking and a Catbox payload host before process injection into svchost.exe.
Figure: Check Point Research, Oct. 27, 2026 (fair use).Attack chain for the GPT-6 Astra wave of the Yoba campaign.

GitHub.io pages described the fake software and linked to ZIP releases hosted on GitHub. The three packages Check Point lists are sol-setup.zip (uploaded Aug. 30), Setup-Claude.zip (Aug. 31) and GPT-6-Astra-Setup.zip (Sept. 4). None of the ZIPs used password protection. Inside each package, Setup.exe is a legitimate signed OpenAI or Anthropic binary; the malicious component is winmm.dll, compiled the same day it was added to the archive. The ChatGPT and Claude packages share the same malicious files and the same indicators of compromise, Check Point says.

Repository authors used different Outlook.com addresses and commit time zones (UTC+4, UTC-4 and UTC+3). Check Point treats the inconsistency as OPSEC rather than as a firm attribution to one geography, though other markers in the malware point toward a Russian-speaking operator.

YobaDropper and the CIS language check

The malicious winmm.dll exposes 180 export names that mimic a real winmm.dll, but every export other than DllEntryPoint contains only a return instruction. Before unpacking its payload, the dropper hashes the basename of its host process with DJB2 and compares it with the hardcoded value 0xE6C2F326, which matches Setup.exe. A failed check does not exit; instead the DLL runs 200,000 iterations of Sleep(5500), about 12.73 days of delay, while appending a filler string to a local buffer.

A second check inspects the system's keyboard layout against a CIS-region bitmask and excludes Russian, Belarusian, Tajik, Armenian, Azerbaijani, Georgian, Kazakh, Kyrgyz, Turkmen, Uzbek and Tatar, with an explicit exception for Ukrainian. If the process is not running as administrator, the dropper shows the message "Please run this program as Administrator." and exits.

When those checks pass, the dropper creates ProgramData\WMProcess, copies WMPDMC.exe from System32 into that folder, XOR-decrypts an embedded payload with the seed IRANNUMBERONE and drops it as wmpdui.dll. Persistence is a scheduled task authored as "Microsoft Corporation," described as collecting device metadata for Windows Media Player, delayed three minutes after boot and running as Local System.

Google Search results captured by Check Point Research for "GPT-6 Astra download free" and "GPT-6 Astra setup," each with the malicious gpt-6-astra.github.io guide ranked near the top.
Screenshot: Check Point Research, Oct. 27, 2026 (fair use).Google results that surface the fake GPT-6 Astra GitHub.io guide.

Telegram image, DGA and DNS over HTTPS

YobaLoader, the second-stage wmpdui.dll, repeats the process-name hash check against WMPDMC.exe (hash 0x552751E3) and uses a different DJB2 seed (0x1DEB) for Windows API resolution. For tasking it decrypts the Telegram channel t.me/yoba_fanclub, downloads the channel's profile image and uses the last 50 bytes as a seed for a domain-generation algorithm of the form adjective-noun-verb-digit.dedyn.io. It then queries https://dns.google/resolve?name=$DGA&type=TXT, verifies an Ed25519 signature on the Base64 data field with the public key published in the report, and decrypts the task with AES-ECB key 1d0d1368b4d53f3a6322cf40e84e63db.

The decrypted response Check Point recovered began with the digit 1 followed by a Catbox URL (files.catbox.moe/z5zpy9.dat). The leading digit selects one of three delivery methods: inject into svchost.exe, write a random .exe under %TEMP% (after clearing Zone.Identifier), or write and run a PowerShell script with -WindowStyle Hidden -ExecutionPolicy Bypass. The injected payload in this wave was XMRig 6.26.0 aimed at a TLS onion mining endpoint through a local Tor SOCKS5 proxy on 127.0.0.1:9550, with WinRing0 loaded when the system is idle. Check Point stresses that YobaLoader is a generic loader; the operator can swap the final stage without changing the dropper.

Side-by-side signature verification panels from Check Point Research showing legitimate signed OpenAI and Anthropic Setup.exe binaries used as DLL-sideloading hosts in the Yoba packages.
Screenshot: Check Point Research, Oct. 27, 2026 (fair use).Signed OpenAI and Anthropic binaries that host the malicious winmm.dll.

Earlier Cursor wave and what SOCs can hunt

An earlier YobaDropper seen in early June 2026 expected the process name Cursor.exe (hash 0x56221573) and used a Startup-folder shortcut under a misspelled "Microsaft Difendir" path instead of a scheduled task. That variant also used the .aber.ir suffix for DGA domains rather than .dedyn.io, and kept anti-debug and anti-VM scoring that newer builds dropped. The Telegram channel and profile image stayed the same across both waves.

For SOC teams, the huntable surface is process-level rather than network-only. Look for Setup.exe or WMPDMC.exe loading winmm.dll or wmpdui.dll from unusual directories; for WMPDMC.exe under ProgramData\WMProcess with a Local System scheduled task that claims to collect Windows Media Player metadata; for DNS-over-HTTPS queries to dns.google that resolve TXT records for *.dedyn.io names in the adjective-noun-verb-digit pattern; and for Tor plus XMRig under a Local\WindowsSecurity mutex. Check Point published YARA rules for both the dropper and the loader, plus SHA1 hashes for the ZIPs, signed hosts, dropper, loader, Telegram image, Catbox payload and XMRig binary.

Sources:


Priya Shah covers threat intelligence, intrusion analysis, and adversary tradecraft for SOCtember from Singapore.

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