AI Email Defense Against ISO Phishing in Finance

Finance teams don’t get breached because they’re careless. They get breached because attackers keep finding file formats and workflows that slip past “normal” controls. ISO attachments are one of those tricks—again.

Researchers recently detailed a phishing campaign (Seqrite Labs calls it Operation MoneyMount-ISO) that targets Russian organizations across multiple industries, with a heavy focus on finance and accounting functions—procurement, legal, payroll, and the teams that approve payments. The emails carry malicious ISO disk images that install Phantom Stealer, a credential and data theft tool.

This is exactly the kind of attack pattern where AI in cybersecurity earns its keep: not by “scanning a file” once, but by correlating weak signals across email content, attachment behavior, user actions, and downstream network activity—fast enough to stop theft before it becomes fraud.

Why ISO phishing works (and why finance is the bullseye)

ISO phishing works because it weaponizes normal enterprise behavior: “open the attachment, review the invoice, approve the request.” An ISO file is essentially a virtual disk. When a user opens it, the operating system can mount it like a CD/DVD, exposing contents that look like ordinary files.

Attackers like ISO attachments for three practical reasons:

• They can hide the real payload inside the mounted image (often a shortcut file, script, or executable disguised as a document).
• They bypass older attachment filters that focus on obvious risky extensions.
• They encourage a click-through workflow (“Open the image, then open the document inside”) that feels routine to busy finance staff.

Finance and accounting teams are targeted because they’re uniquely positioned to convert stolen credentials into money. I’ve seen this pattern repeatedly: attackers don’t need domain admin on day one—if they can compromise an inbox tied to payments, vendors, payroll, or procurement, they can pivot into business email compromise (BEC), invoice redirection, and payroll fraud.

The seasonal angle: year-end pressure makes this easier

It’s December 2025. Finance departments are closing books, reconciling vendors, handling bonuses, and pushing last-minute purchases through approvals. That creates perfect cover for:

• “Urgent” invoice review requests
• Vendor “bank detail updates”
• Payroll corrections
• Contract attachments from legal/procurement

Attackers don’t need perfect social engineering—just timing. And year-end timing is a force multiplier.

What Phantom Stealer campaigns typically try to steal

A stealer like Phantom Stealer is built for speed: infect, harvest, exfiltrate, and move on. While individual variants differ, stealers commonly target:

• Browser-stored passwords and cookies (often enough to hijack sessions)
• Email and VPN credentials
• Messaging and collaboration tokens
• Autofill data that contains addresses, card details, or identity info
• Local files in common folders (downloads, documents), especially anything that smells like finance or authentication

The outcome isn’t just “data loss.” In finance environments, credential theft often becomes:

• Fraudulent payment approvals
• Fake vendor onboarding
• Supplier invoice rerouting
• Internal phishing from a trusted mailbox

A stealer infection is rarely the end of an incident. It’s the access sale, the BEC setup, or the prelude to ransomware.

Where traditional email security falls short with ISO attachments

Most companies still run email security as if the world is dominated by PDF macros and obvious executables. That’s not the world you’re living in.

Here’s where legacy controls struggle with ISO phishing:

1) “Allowed attachment types” is a blunt instrument

Blocking every archive-like format can break legitimate workflows. Many organizations end up allowing too much “because business.” ISO gets through.

2) Signature-based detection is late by design

If your detection depends on known hashes or known payload signatures, you’re always behind. A phishing actor can repackage the same malware in minutes.

3) Sandboxing isn’t guaranteed to detonate the right behavior

ISO payloads can be staged to avoid automated analysis—requiring specific user interactions, timing, or environment cues. If the sandbox doesn’t emulate the full chain, it can miss the real dropper behavior.

4) The real attack is multi-step and cross-channel

The email is step one. The mount is step two. The execution and credential harvest is step three. Traditional tools often evaluate each stage separately instead of connecting them.

How AI stops ISO phishing before it turns into credential theft

AI-based email security is most effective when it’s treated as a system (email + endpoint + identity + network), not a single filter. The win is correlation.

AI signal #1: Attachment and delivery pattern anomalies

Even when the payload is “new,” the campaign mechanics often repeat. AI models can flag:

• Unusual use of ISO attachments for a sender/recipient pair
• First-time sender patterns that mimic vendor identities
• Spikes in similar subject lines or invoice templates across mailboxes
• Lookalike sender domains and subtle header inconsistencies

This is where anomaly detection shines: it doesn’t need the attacker’s exact malware hash—just the reality that your procurement inbox doesn’t normally receive ISO images.

AI signal #2: Language and intent detection that’s finance-aware

Generic phishing detection misses a lot of finance lures because the content “looks professional.” AI that understands business context can score risk based on:

• Payment urgency language (“today,” “overdue,” “final notice”)
• Bank detail change requests
• Attachment instructions that add friction (“mount/open/run”)—a red flag in itself
• Social-engineering patterns targeting approval workflows

A practical stance: any email asking a finance user to mount a disk image should be treated as suspicious until proven otherwise.

AI signal #3: User behavior that doesn’t match the person

The most valuable detection often happens after delivery but before damage. Behavioral analytics can spot:

• A user who rarely opens attachments suddenly mounting disk images
• Unusual login locations or device fingerprints after an attachment open
• First-time OAuth token grants or suspicious session activity
• Rapid mailbox rule creation (common in BEC follow-on activity)

If you can catch the “weird” within minutes, you can invalidate sessions, rotate credentials, and block exfiltration.

AI signal #4: Fast enrichment from automated threat intelligence

Attackers don’t run one campaign—they run variants. AI-assisted threat intelligence can automatically:

• Cluster related emails by template, infrastructure, and attachment traits
• Push detections across the environment once one user reports an email
• Prioritize incidents based on blast radius and privilege level

Speed matters. If the first compromised user is in payroll, you want containment actions in motion immediately—not after a human triage queue clears.

Three signs your email system is vulnerable to Phantom Stealer-style ISO phishing

If any of these are true, you’re easier to hit than you think:

1. ISO/VHD/VHDX attachments aren’t explicitly controlled (blocked, quarantined, or detonation-required).
2. Finance mailboxes don’t have stronger policies than the rest of the company (they should).
3. You can’t correlate email events with endpoint behavior (attachment opened → process executed → credential access).

That third point is the silent killer. Many organizations can tell you an email arrived, but they can’t tell you what happened next—until fraud shows up.

A practical defense plan: what to do this week

You don’t need a “rip and replace” program to reduce risk quickly. Start with controls that are high-signal for ISO phishing.

Tighten policy around disk image attachments

• Quarantine or block ISO by default for finance and accounting groups.
• If blocking isn’t possible, route to detonation analysis plus a manual review step.
• Treat LNK, JS, VBS, HTA, and unexpected executables inside mounted images as auto-malicious.

Add identity protections that assume credentials will be targeted

• Enforce phishing-resistant MFA where possible.
• Disable legacy authentication paths.
• Monitor for impossible travel, token replay, and unusual session persistence.

Use AI-driven anomaly detection for finance workflows

Focus AI on the highest-loss scenarios:

• Vendor bank changes
• Invoice payment approvals
• New payee setup
• Payroll profile changes

If an endpoint mounts an ISO and the same user initiates a vendor payment change within an hour, that’s not “maybe suspicious.” That’s a stop-the-line event.

Run a finance-specific phishing tabletop (30–45 minutes)

Keep it simple and realistic:

• Who verifies vendor changes?
• What’s the out-of-band confirmation method?
• Who can freeze payments?
• How fast can you invalidate sessions and reset credentials?

A tabletop isn’t a compliance exercise. It’s where you find out if your process actually prevents money from leaving.

People also ask: ISO phishing and AI email security

Why do attackers use ISO files in phishing emails?

They use ISO files because they act like containers that can hide the real malware and encourage a multi-step workflow that bypasses basic attachment filters.

Can AI detect phishing emails with new malware?

Yes—when AI is used for pattern and anomaly detection, it can flag suspicious attachment types, sender behavior, and user actions even if the malware hash is brand new.

Should organizations block ISO attachments entirely?

For most departments, yes. For teams that truly need them, require detonation, strict allowlisting, and extra user verification. Finance teams should be the strictest by default.

Where this fits in the “AI in Cybersecurity” series

A lot of security content focuses on big-ticket threats like ransomware. This ISO phishing campaign is a reminder that small, repeatable intrusions—credential theft, session hijacking, mailbox takeover—cause huge downstream damage, especially in finance.

AI in cybersecurity is most useful here when it’s doing what humans can’t at scale: spotting weak signals across thousands of messages and turning them into a clear decision—quarantine the email, isolate the endpoint, challenge the login, freeze the payment workflow.

If you’re responsible for finance security, this is the question to ask internally: Would we detect an ISO-based phish by behavior, or only after someone reports it? The gap between those two answers is where breaches live.