Threat Actors Behind WARMCOOKIE Malware Added New Features to It’s Arsenal

The WARMCOOKIE backdoor first surfaced in mid-2024, delivered primarily via recruiting-themed phishing campaigns that coaxed victims into executing malicious documents.

Initially designed as a lightweight implant for remote command execution, its modular codebase enabled rapid adaptation to new objectives.

Over the past year, targets have included enterprise networks across multiple regions, with operators exploiting malvertising and spam campaigns to seed infections.

These intrusions have allowed threat actors to maintain persistent footholds, steal credentials, and deploy secondary payloads.

Elastic Security Labs analysts identified ongoing updates to WARMCOOKIE’s infrastructure and code family shortly after the initial disclosure.

By mid-2025, the backdoor was implicated in Europol’s Operation Endgame, yet infections persisted through revamped delivery mechanisms.

While earlier variants relied on hardcoded folder paths and static mutex names, recent builds leverage dynamic string banks and dual GUID-style mutexes for improved stealth.

Beyond simple command handlers, the malware now incorporates new capabilities to launch executables, DLLs, and PowerShell scripts on demand.

Each command type is routed through a unified function that writes the payload into a temporary directory before execution, either by invoking rundll32.exe for DLLs or PowerShell.exe for scripts.

This expansion broadens WARMCOOKIE’s utility as a flexible loader, accommodating custom modules without altering the core binary.

Infection Mechanism

WARMCOOKIE’s infection mechanism has evolved to evade static detection and complicate incident response.

Upon execution, the backdoor parses a configuration blob embedded within its resource section, decrypting fields such as the Remote Command and Control (C2) URL, RC4 key, and a campaign identifier.

The decryption routine resembles the following pseudocode:-

DWORD seed = GetTickCount();
srand(seed);
int index = rand() % STRING_BANK_SIZE;
char *path = string_bank[index];
desStringDecrypt(dword14001B620, buffer, bufferSize);

This snippet illustrates how WARMCOOKIE seeds its random number generator with the system uptime, selects a legitimate-looking folder name from a dynamic list, and decrypts campaign parameters at runtime.

The campaign ID field, introduced in later versions, enables operators to tag infections with distribution context—such as “traffic2”—facilitating granular tracking of victim sets.

After decryption, the malware establishes persistence by creating a scheduled task whose name and executable path mirror recognized software vendors drawn from the same string bank.

This shows a sample scheduled task entry where the task name and folder path reference a legitimate IT services company name.

By randomizing folder names and task identifiers, WARMCOOKIE avoids repeating known artifacts across samples, complicating signature-based detection.

In parallel, dual GUID-style mutexes regulate initialization sequences, ensuring only a single instance runs and mitigating race conditions during startup.

Collectively, these enhancements underscore the attackers’ emphasis on resilience and evasion, reinforcing WARMCOOKIE’s position as a persistent threat to enterprise environments.

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