Infostealers

What is an Infostealer? 

Infostealer malware is designed to infiltrate a device and exfiltrate data such as login credentials, session cookies, financial details, and personally identifiable information, typically to a server controlled by attackers. But unlike ransomware, which announces itself, a breach by an infostealer is often invisible to the victim, since the malware’s primary goal is to harvest the data and get away with it all. Many infostealers are non‑persistent, executing an attack and removing themselves in mere seconds, leaving little to no forensic trace on the device. 

In practice, an infostealer breach compromises a legitimate device and takes a user’s browser-stored credentials and session tokens. Stealer logs like these are used by malicious actors to execute account takeovers (ATOs) and further infiltrate corporate environments. 

How Infostealers Work 

Infostealers generally target victims using a common vector for malware delivery, like  phishing emails, drive-by downloads from compromised or malicious websites, malvertising campaigns, and trojanized software such as “free” cracked apps and game mods. Social engineering and search engine optimization (SEO) poisoning are also common methods to convince users to download infostealer malware posing as legitimate products or updates. 

Once a network is infected, the malware begins collecting data using such methods as: 

• Capturing keystrokes 
• Hijacking web form submissions before encryption 
• Scanning files and emails 
• Collecting browser cookies and session tokens 
• Searching for crypto wallet data stored locally 

The data harvested is then exfiltrated to attacker infrastructure over HTTP/HTTPS or other channels, and then packaged into stealer logs that are sold or traded on centralized markets, decentralized Telegram bots, or private channels for money for follow‑on attacks by other attackers. 

Types of Infostealers 

Although their types vary, the majority of the infostealers are divided into a few categories: 

• Browser-focused infostealers: Targets include saved passwords, autofill, cookies, and session tokens from browsers to achieve an automatic account takeover which does not require password cracking. 
• Credential and form grabbers: Intercepts login fields and payment forms in real-time, collecting usernames, passwords, card numbers and other information before it is encrypted in transit. 
• Keylogger-based infostealers: Records keystrokes for an attacker to recover credentials, chats as well as other vulnerable text input. 
• Crypto wallet stealers: Looks for installed wallet apps and private keys, which are then exfiltrated so attackers can steal crypto assets. 
• Multi-function infostealers: Blends several of the capabilities outlined above, often provided as malware‑as‑a‑service (MaaS), to lower the barrier for non‑technical attackers to stage infostealer attacks. 

Many infostealer campaigns will also integrate with other malware or tools, such as loaders or remote access trojans to maintain access, or by feeding stealer logs into automated credential stuffing platforms. 

Signs of an Infostealer Infection 

As infostealers are meant to stay hidden, visible symptoms at the endpoint are frequently very small or nonexistent. But downstream indicators that can suggest an earlier infostealer leak are common. These include:

• Unexpected login alerts, password reset emails, new sign‑ons on personal or corporate accounts, all especially bundled in a brief period. 
• False transactions, modifications to payment info or new accounts created in your name, typically implying stolen financial or identity information. 
• Notifications received at services that monitor for leaked credentials or stealer logs. 
• Evidence of credential stuffing or account takeover attempts against corporate applications, especially when the stolen log is linked to stealer logs and has cookies and new passwords. 

For defenders, a discovered infostealer log linked to a user or device is itself a strong sign of an infection that may have already removed itself, making external visibility into stealer logs critical. 

How To Protect Against Infostealers 

Reducing infostealer risk requires endpoint hygiene, privacy awareness and visibility into stealer logs. This means:

• Hardening endpoints: Keep operating systems, browsers, and plugins up to date, install reputable antivirus software, and make sure real‑time scanning is enabled. 
• Strengthening access and identity: Use unique passwords and a password manager, enable multi‑factor authentication wherever possible, and prioritize phishing‑resistant factors for high‑value accounts. 
• Limiting browser exposure: Minimize saving passwords and payment details in browsers when possible, regularly clear cookies and session data to reduce the usefulness of stolen tokens. 
• Educating users: Instruct staff to identify phishing, malvertising and fake download websites, and to avoid cracked or pirated software and unofficial mods. 
• Leveraging infostealer checks and dark web monitoring: Employ digital services that continuously analyze domains, users, and customers in stealer logs and other criminal datasets to respond quickly to new compromises as they happen. 

Operationally, a good post‑infection playbook for organizations should include automatic invalidation of exposed credentials and session tokens, device triage in case of attack and user access, the ability to monitor for follow‑on activity like account takeover and lateral movement. 

Repercussions of Infostealer Attacks 

Infostealer attacks may result in account takeover, identity theft, financial fraud and unauthorized access of corporate data. When using stealer logs containing “in‑use” credentials and cookies that have not yet expired to populate user credentials, attackers have a very high success rate, especially when using such logs for credential stuffing, session hijacking, and targeted intrusion attempts. 

For organizations, the downstream impact can result in data breaches, ransomware, regulatory exposure, and reputational risk when customer data is compromised. The non‑persistent nature of many infostealers means standard endpoint tools may not capture anything. This means security teams have no choice but to depend on external visibility into exfiltrated information in order to determine what was stolen and enable a holistic remediation. 

FAQs 

What types of personal metadata do infostealers aim for? 

Infostealers are able to gather login credentials, session cookies, financial information, identity data, browser history, chat logs, documents, images and crypto wallet keys from an infected device. Indeed, many contemporary families are beginning to exfiltrate multi‑factor tokens and passkeys as well, so that new accounts have the potential to be hijacked in an escalated manner, even with MFA-enabled multi‑factor authentication. 

Do mobile devices have an increased risk of being compromised by an infostealer attack? 

Yes. While a great many well‑known infostealers target desktop environments, similar techniques can also be leveraged with mobile platforms through malicious apps, phishing and browser‑based exploits. With more and more authentication and financial activity shifting to mobile, the incentives for infostealers to target phones or tablets are rising. 

If it seems I have information stolen, what do I do? 

If you get an infostealer check alert, or suspect that your data is in stealer logs, immediately change passwords on affected accounts, revoke active sessions, and if you can, enable or reset MFA. Ensure you are also auditing your financial statements and identity alerts, running a full malware scan on your devices and in a corporate context, getting your security team to handle complete post‑infection remediation. 

Are infostealers capable of hiding from normal security scans? 

Infostealers typically evade endpoint defenses and may perform and self‑delete quickly without leaving behind evidence. Research suggests a large proportion of malware infections happen on devices where endpoint security is already deployed, stressing the importance of additional defenses and exposure from exfiltrated stealer logs, as opposed to relying solely on local detection. 

In what sectors are infostealer attacks most likely to take place? 

Any industry containing sensitive credentials or financial and personal information is threatened, including finance, ecommerce, technology, healthcare and government. Organizations with big remote or browser‑heavy workforces are particularly at risk, as browser-stored credentials and session cookies from infostealer breaches can give attackers direct access to SaaS applications and other internal systems.