In recent years, the cybersecurity landscape has witnessed a notable rise in the exploitation of Windows shortcut files, commonly known as LNK files, for the delivery of malware. Our telemetry data indicates a significant increase in malicious LNK samples, with figures jumping from 21,098 in 2023 to an alarming 68,392 in 2024. This article delves into a comprehensive analysis of LNK malware, drawing insights from the examination of 30,000 recent samples.
LNK Files Explained
LNK files serve as virtual links that facilitate easy access to files, folders, or applications within the Windows operating system. These files, identifiable by their .lnk extension, allow users to launch programs without navigating through complex directory structures. However, this same flexibility renders LNK files a potent weapon for cybercriminals, enabling them to execute malicious content while masquerading as legitimate files.
Creating an LNK file is straightforward, typically involving a right-click in File Explorer and selecting the “Create shortcut” option. This simplicity, combined with the ability to customize icons and filenames, often leads users to unwittingly open malicious files that appear harmless.
Important Structures for LNK Malware
The binary structure of LNK files contains several critical fields that can indicate malicious intent. Our analysis reveals that three fields are particularly significant:
- LINKTARGET_IDLIST: This field specifies the target location of the LNK file.
- RELATIVE_PATH: This provides the relative path of the target concerning the LNK file.
- COMMANDLINEARGUMENTS: This field can include arguments passed to the target, potentially executing malicious scripts.
Our findings indicate that 99.53% of malicious LNK files contain the LINKTARGETIDLIST, while 75.49% include the RELATIVEPATH. The COMMANDLINEARGUMENTS field appears in 35.52% of these files, underscoring its role in executing harmful code.
LNK Malware Categories and Examples
Our research categorizes LNK malware into four distinct types:
- LNK exploits
- Malicious file execution
- In-argument script execution
- Overlay content execution
LNK Exploits
The first category involves exploit-based LNK files designed to take advantage of vulnerabilities in the Windows operating system. Although the prevalence of these exploits has diminished due to patches from Microsoft, understanding their mechanics remains crucial for cybersecurity professionals.
Malicious File Execution
This type of LNK malware does not contain harmful content itself but instead executes malicious files already present on the victim’s system. For instance, an LNK file may link to a malicious executable saved in the user’s Downloads folder.
In-Argument Script Execution
Here, the COMMANDLINEARGUMENTS field can contain malicious scripts that are executed by pointing the LNK file to a script interpreter like cmd.exe or powershell.exe. This method often employs obfuscation techniques to evade detection.
Overlay Content Execution
In this technique, attackers append malicious scripts or payloads to legitimate LNK files. By utilizing commands like find or mshta, they can execute hidden content without raising suspicion.
As LNK files continue to evolve as a vector for malware distribution, it is imperative for both cybersecurity experts and everyday users to remain vigilant. Users should exercise caution when handling unknown LNK files, particularly those downloaded from the internet. To identify potential threats, it is advisable to inspect the properties of LNK files, focusing on their target locations and any unusual characteristics.
For organizations seeking enhanced protection against these threats, Palo Alto Networks offers a suite of products designed to defend against LNK malware, including:
- Next-Generation Firewall with cloud-delivered security services, including Advanced WildFire.
- Prisma Access devices with integrated security services.
- Advanced Threat Prevention featuring machine learning-based detection capabilities.
- Cortex XDR and XSIAM agents for multi-layered protection against post-exploitation activities.
In the event of a suspected compromise, users are encouraged to reach out to the Unit 42 Incident Response team for immediate assistance.
Indicators of Compromise
For those analyzing potential threats, the following SHA256 hashes of LNK malware samples may serve as indicators of compromise:
- a90c87c90e046e68550f9a21eae3cad25f461e9e9f16a8991e2c7a70a3a59156
- 08233322eef803317e761c7d380d41fcd1e887d46f99aae5f71a7a590f472205
- 9d4683a65be134afe71f49dbd798a0a4583fe90cf4b440d81eebcbbfc05ca1cd
- a89b344ac85bd27e36388ca3a5437d8cda03c8eb171570f0d437a63b803b0b20
- 28fa4a74bbef437749573695aeb13ec09139c2c7ee4980cd7128eb3ea17c7fa8
- fb792bb72d24cc2284652eb26797afd4ded15d175896ca51657c844433aba8a9
- f585db05687ea29d089442cc7cfa7ff84db9587af056d9b78c2f7a030ff7cd3d
- b2fd04602223117194181c97ca8692a09f6f5cfdbc07c87560aaab821cd29536
- 86f504dea07fd952253904c468d83d9014a290e1ff5f2d103059638e07d14b09
- d1dc85a875e4fc8ace6d530680fdb3fb2dc6b0f07f892d8714af472c50d3a237
- 76d2dd21ffaddac1d1903ad1a2b52495e57e73aa16aa2dc6fe9f94c55795a45b
