What is infostealer malware, and how it steals corporate credentials

Infostealer malware is lightweight software that silently harvests credentials, session cookies, authentication tokens and autofill data from an infected device, then exfiltrates them to an attacker. The stolen bundle, called a stealer log, gets sold on criminal markets and often becomes the first step into a corporate network. SpyCloud alone recaptured 548 million such credentials in 2024.

What is infostealer malware?

Infostealer malware is a class of trojan built to steal secrets, not to encrypt or destroy. It copies passwords, cookies, tokens and crypto wallets from a device, then ships them to an operator. Credential theft from password stores now appears in 25% of analyzed malware samples, a threefold rise (Picus Red Report 2025).

These tools run as malware-as-a-service. Operators rent a builder, spread it through cracked software, phishing and malicious ads, then resell whatever comes back. IBM X-Force logged an 84% jump in emails delivering infostealers in 2024 (IBM X-Force). The barrier to entry is low, and the payoff is a working corporate login.

The names change, but the pattern holds. Families like RedLine, LummaC2 and StealC dominate, each sold on subscription with fresh evasion baked in. Take one offline and another fills the gap within weeks. For a defender, the specific strain matters far less than the output: a fresh log with your users inside it.

Infostealers have quietly rewritten the economics of intrusion. Rather than crack a network, an attacker buys a log for a few dollars and signs in with valid credentials. Identity abuse drove 30% of incidents in 2024, the single top entry point that year (IBM X-Force). Why break in when you can log in?

How do infostealers steal corporate credentials?

Infostealers pull credentials straight from where the browser keeps them. They decrypt saved logins, copy the cookie database, scrape autofill and read local token files, all in seconds. SpyCloud tied 548 million exfiltrated credentials to infostealer malware in 2024 (SpyCloud). On a work device, that haul includes SSO and VPN logins.

A stealer log is a snapshot of one device, not a single leaked table. Unpack a typical log and you find:

• Passwords saved in Chrome, Edge and Firefox, paired with their exact login URLs
• Active session cookies and refresh tokens for email, SSO and cloud consoles
• Autofill data, including names, addresses and payment fields
• A system fingerprint: hostname, operating system, installed apps and local IP
• Cryptocurrency wallets and, on developer machines, API keys and .env files

The corporate risk hides in the mix. Verizon found 46% of systems holding company logins were unmanaged devices, meaning personal laptops outside EDR coverage (Verizon 2025 DBIR). A contractor's home PC gets infected, and its saved corporate password lands in a log your SOC never sees.

The stolen-credential attack chain, step by step

A stolen credential rarely gets used the moment it is taken. It moves through a supply chain: infection, exfiltration, listing, sale, then access. Verizon named stolen-credential use the top initial-access action in 22% of breaches (Verizon 2025 DBIR). Each handoff adds buyers, and speed favors the attacker.

• Infection: a user runs cracked software or a malicious attachment, and the stealer executes once.
• Exfiltration: the log is bundled and sent to the operator's server or a Telegram channel in seconds.
• Listing: the log is parsed for corporate domains, then posted to a market or shared in bulk.
• Access: a buyer replays the session cookie or logs in, then pivots toward email, SSO and VPN.
• Impact: valid access becomes data theft or a ransomware foothold.

Timing is the defender's problem. Median dwell time sits at 11 days, but stretches to 26 days when an outside party raises the alarm instead of your own team (Mandiant M-Trends 2025). The earlier you spot the exposed identity, the shorter that window gets.

Why can't a password reset fix a stealer log?

Because the attacker often does not need the password. A stealer log usually contains a live session cookie, which represents an already-authenticated session. Replaying it skips the login form and the MFA prompt entirely. SpyCloud recaptured 17.3 billion such cookies in 2024 (SpyCloud). Resetting the password leaves that session valid.

Here is the part most playbooks miss. A password reset invalidates a secret the attacker may not even be using. The session token is a separate credential with its own lifetime, and it survives the reset until it expires or is explicitly revoked. Containment means killing active sessions, not just rotating passwords (Recorded Future).

Not every log carries a usable cookie, but plenty do. Flashpoint found more than 4.2% of infostealer-exposed credentials include browser cookies that can support session hijacking (Flashpoint). Across billions of records that slice is enormous, and each cookie is a ready-made bypass around the MFA a team worked hard to deploy.

What makes infostealer exposure so hard to detect?

Scale and location. The recaptured identity pool reached 53.3 billion distinct records in 2024, up 22% year over year (SpyCloud). Much of that theft happens on devices your controls never touch, so no endpoint alert ever fires. The exposure is real, yet invisible from inside the perimeter.

Consider where the infection sits. A personal laptop, a contractor's desktop or a phone syncing a work password manager falls outside EDR and MDM. The credential leaks, the session is captured, and the first signal you get is a login from an odd location, if you get one at all. Isn't that exactly the alert that lands too late?

This is why exposure monitoring works from the outside in. Watching the criminal supply of stealer logs for your domains surfaces the compromise before the login attempt, not after it. That is a different signal than a SIEM rule, and it closes the gap an unmanaged device quietly leaves open.

How big is corporate infostealer exposure in 2025?

The volume keeps climbing. Flashpoint counted 11.1 million devices infected by infostealers in 2025, spilling roughly 3.3 billion credentials, cookies and tokens (Flashpoint). In the first half of 2025 alone, stolen credentials jumped 800% year over year. This is not a fringe threat; it is the mainstream way in.

The link to ransomware is direct. Verizon reported that 54% of 2024 ransomware victims had their domains show up in infostealer credential dumps beforehand (Verizon 2025 DBIR). Stealer logs act as the reconnaissance and the key at once: buy the log, find the VPN login, deploy the payload.

The password problem is compounding too. SpyCloud recaptured 3.1 billion plaintext passwords in 2024, a 125% jump, and reuse means one leaked password can open several corporate doors (SpyCloud). Volume like this is why credential-based intrusion keeps outpacing patched exploits.

What does defensible infostealer containment look like?

Speed and proof both matter. Median attacker dwell time is now 11 days (Mandiant M-Trends 2025), and the global average breach costs 4.44 million dollars (IBM). A defensible response detects the exposed identity, validates whether the credential and session are still live, then remediates each one on the record.

The workflow has three moves: find every exposed identity across the workforce and customer base, confirm what is still valid, and revoke it with an auditable trail. This post-compromise exposure model is what Ashetrace is built around. You verify a domain you control, and no passwords, cookies or tokens ever change hands.

Cost sharpens the point. A US breach now averages 10.22 million dollars, a record high (IBM), and the human element still factors into roughly 60% of breaches (Verizon 2025 DBIR). Faster identity containment is among the cheapest controls you can apply once a log leaks.

So the question is not whether your people appear in a stealer log. At current volumes, some already do. The useful question is how fast you can find them and cut the live sessions before someone else does.