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A Deceptive Email With a Much More Dangerous Payload
Malware rarely arrives looking like malware. In this case, the infection began with what appeared to be a routine Brazilian Portuguese email asking the recipient to sign a digital contract. Behind that familiar business theme was a carefully engineered delivery chain designed to behave differently depending on where the victim was located and how their Windows system was configured.
On August 31, 2026, security researcher Bradley Duncan analyzed and deliberately executed the malicious link inside a controlled Windows laboratory environment. The resulting infection was identified as Guildma, also known as Astaroth, a malware family historically associated with Brazilian and Latin American campaigns.
What makes this incident particularly interesting is not simply the malware itself, but the amount of environmental checking performed before the payload was delivered. The campaign used geographic and language-based filtering, hiding its malicious behavior from systems that did not appear to be Brazilian targets.
The Attack Begins With a Fake Digital Contract
The campaign started with an email pretending to come from a digital-document service. Its subject was designed to create urgency and curiosity:
“Assine com o Docusing: CONTRATO_ASSINATURA_FINAL…”
The wording translates roughly to “Sign with Docusing: FINAL_SIGNATURE_CONTRACT…”
The sender used a suspicious .cfd domain rather than a legitimate document-signing service, while the message itself was written in Brazilian Portuguese.
That combination is important because the attackers were not simply sending malware indiscriminately. They were constructing a convincing regional lure aimed at users who would reasonably expect Portuguese-language contract notifications.
The Campaign Was Geofenced
One of the most revealing characteristics of this infection was its geofencing.
The malicious URL did not immediately provide the same content to every visitor. According to the analysis, the infrastructure checked whether the request appeared to originate from Brazil.
If the visitor did not satisfy the expected conditions, the server could instead return a legitimate installer—in this case, an Android Studio installer.
This is a classic defensive-evasion technique from the attacker’s perspective.
Security researchers working outside Brazil could therefore visit the URL and see nothing obviously malicious. Automated scanners operating from another country could also receive benign content.
The campaign additionally required Brazilian Portuguese language and regional settings on the victim’s browser and operating system.
That creates several layers of filtering:
Location → Language → Regional configuration → Payload delivery
The more conditions an attacker checks, the harder it becomes for automated security researchers and sandbox environments to reproduce the attack.
The Initial Payload Was a ZIP Archive
Once the appropriate environmental conditions were satisfied, the victim received a ZIP archive.
The archive was relatively small, measuring only 1,661 bytes, but contained a Windows shortcut.
Its SHA-256 hash was:
cc44782356cb0effc528a7ab22c19ab360a55ebbbe01feb0967031aa191c5869
The extracted shortcut was named:
868283789726483.lNk
Its SHA-256 hash was:
47d2908c4dd7f6f5eb4a8ef4306077b10315c44231f4bacd2bb811b245561911
The use of a Windows shortcut is significant because .LNK files can launch commands and programs without appearing to be traditional executable malware.
For an unsuspecting recipient, opening what appears to be a document-related file can therefore trigger an entirely different process in the background.
The Shortcut Concealed the Next Stage
The shortcut did not simply launch the malware directly.
Instead, it retrieved additional content from remote infrastructure and stored that content inside an NTFS alternate data stream, or ADS.
The file was created beneath the
C:Users[username]AppDataLocalTempn1LUQ7.log:h6JSb
The portion after the colon is the alternate stream.
This technique is particularly interesting because alternate data streams can hide information within a file without appearing in the ordinary contents of that file.
To a casual user browsing the directory, n1LUQ7.log may look like an ordinary log file.
The actual malicious content, however, was stored in its hidden stream.
The Hidden DLL Did Not Look Obviously Malicious
The ADS contained a 64-bit Windows DLL.
Its SHA-256 hash was:
a6044786991afdb9d42ceb350943987765a7d0e8537369b2092e3f019c0f63ca
The DLL was approximately 266 KB in size and identified as a PE32+ x86-64 Windows GUI DLL.
Interestingly, the researcher noted that the DLL itself did not appear malicious.
That is an important detail.
Modern malware campaigns do not necessarily need every component of their delivery chain to be independently malicious. Attackers can use apparently benign components as loaders, execution mechanisms, or intermediaries.
The suspicious behavior becomes visible when the components are analyzed together.
AutoIt Becomes the
The DLL was ultimately used to retrieve and install an AutoIt package associated with Guildma.
The persistent Guildma component was identified as a compiled AutoIt script.
Its SHA-256 hash was:
f62a958faf0491b2b2803be2ee69b664b58e4a1261f64e8530cdc1a3ff666aa4
The file measured approximately 278 KB and was stored at:
C:UsersPublicLibraries.cachePLAXBeatz.LEDPRO.09662.8729.422.log
The filename and directory structure are another example of camouflage.
A .log extension inside a directory resembling a software cache does not immediately suggest a malicious executable.
The attackers were effectively building a chain in which individual artifacts could appear harmless while the complete sequence produced a malware infection.
Guildma Is the Final Objective
The infection ultimately delivered Guildma, also known as Astaroth.
Guildma is a long-running malware family associated particularly with Brazil and Latin America. It has historically been used for credential theft, information gathering, and other forms of financial or account-focused cybercrime.
The name Astaroth has appeared repeatedly in security research over the years because campaigns involving the malware have demonstrated sophisticated execution and evasion techniques.
The current infection therefore represents more than an isolated malicious ZIP file.
It demonstrates how an established malware family can continue adapting its delivery mechanisms.
HTTPS Makes the Traffic Less Obvious
During the infection, the Windows host communicated with multiple domains over HTTPS on TCP port 443.
Observed infrastructure included:
ekg3h4htc0h0ggdh.canadacentral-01.azurewebsites[.]net
plosancol.aguamammillaria[.]cfd
crironxil.aguasedum[.]cfd
The host also generated TCP traffic toward:
omzagdmspc.a.pinggy[.]link:21601
Using HTTPS makes network detection more difficult because the contents of the communications are encrypted.
Security teams therefore need to rely increasingly on metadata, DNS activity, endpoint telemetry, process behavior, certificate information, destination reputation, and unusual execution chains.
Cloud Infrastructure Can Be Abused as Cover
One of the domains used in the campaign was hosted through an Azure App Service-style hostname.
That is an important defensive lesson.
Attackers do not always need to operate obvious dedicated command-and-control servers. Cloud platforms can provide infrastructure that blends into legitimate enterprise traffic.
An organization that blocks only obviously suspicious hosting providers can therefore miss malicious activity occurring through mainstream cloud services.
This does not mean cloud platforms themselves are malicious.
It means defenders need to distinguish trusted infrastructure from trusted behavior.
GitHub Appears in the Broader Campaign Context
The analysis also observed later HTTPS connections involving legitimate WhatsApp and GitHub domains.
Those domains were not included as malicious indicators because the services themselves are legitimate.
However, previous reporting has documented campaigns abusing GitHub in related activity.
This distinction matters enormously when building detection rules.
Blocking GitHub or WhatsApp outright would create enormous operational problems for legitimate users.
A better approach is to identify unusual processes communicating with those services, suspicious URLs, abnormal authentication patterns, unexpected downloads, and connections occurring immediately after malicious script execution.
Why the Regional Targeting Matters
The Brazilian targeting provides one of the strongest clues about the campaign’s sophistication.
A generic malware campaign might simply send the same payload to everyone.
This one effectively asks:
Are you in Brazil?
Is your system configured for Brazilian Portuguese?
Does your browser look like a Brazilian
Only after those checks does the malicious delivery chain become available.
This dramatically reduces the number of environments in which the malware can be observed.
It also makes automated analysis more difficult.
The Human Element Remains the Weakest Link
Despite all the technical complexity, the attack still begins with a simple social-engineering trick.
The recipient sees a message about an important contract.
The subject suggests that the document is final.
The sender appears related to a digital-signing process.
The natural reaction is to click.
That is why phishing remains effective even when attackers use highly technical malware delivery mechanisms.
The victim does not need to understand what an alternate data stream is.
They only need to believe that the contract is real.
Deep Analysis
Understanding the Attack Chain
The infection can be understood as a sequence of stages:
Phishing email → Geofenced URL → ZIP archive → LNK shortcut → ADS payload → DLL → AutoIt → Guildma persistence → HTTPS communications
Each stage creates another opportunity for defenders to detect the attack.
The advantage for attackers is that no single artifact necessarily tells the complete story.
Inspecting Alternate Data Streams
Windows administrators can inspect NTFS alternate data streams with PowerShell.
Get-Item -Path "C:\Users[username]\AppData\Local\Temp 1LUQ7.log" -Stream
To inspect a specific stream:
Get-Content -Path "C:\Users[username]\AppData\Local\Temp 1LUQ7.log" -Stream "h6JSb"
For forensic work, avoid executing suspicious content merely to determine what it is.
Instead, collect it safely and analyze it in an isolated environment.
Searching for Suspicious ADS Activity
Defenders can search for files containing alternate streams:
Get-ChildItem -Path "C:\Users" -Recurse -Force -ErrorAction SilentlyContinue | Get-Item -Stream -ErrorAction SilentlyContinue
This can generate considerable output on a real system, so production detection should be more targeted.
The key behavioral signal is not simply “ADS exists.”
The stronger signal is:
A user-launched process creates an ADS containing executable content and subsequently executes another process.
Examining Windows Shortcut Files
Security teams should treat unexpected .LNK files received through email as potentially dangerous.
A basic investigation can begin with:
Get-ChildItem "$env:USERPROFILE\Downloads" -Filter .lnk -Force
For enterprise environments, endpoint telemetry should capture the process launched by the shortcut and its command-line arguments.
This is particularly important because malicious shortcuts frequently act as execution wrappers rather than traditional malware files.
Checking Network Connections
During an active investigation, defenders can inspect established connections:
Get-NetTCPConnection -State Established | Select-Object LocalAddress,LocalPort,RemoteAddress,RemotePort,State
DNS resolution can also be examined:
Resolve-DnsName ekg3h4htc0h0ggdh.canadacentral-01.azurewebsites.net
These commands are useful for triage, but they should not be treated as complete malware detection mechanisms.
Hunting for the Observed Hashes
The SHA-256 indicators can be searched across EDR, SIEM, malware repositories, and forensic collections.
cc44782356cb0effc528a7ab22c19ab360a55ebbbe01feb0967031aa191c5869
47d2908c4dd7f6f5eb4a8ef4306077b10315c44231f4bacd2bb811b245561911
a6044786991afdb9d42ceb350943987765a7d0e8537369b2092e3f019c0f63ca
f62a958faf0491b2b2803be2ee69b664b58e4a1261f64e8530cdc1a3ff666aa4
However, hash-based detection alone is insufficient.
The original analysis correctly points out that some hashes may be unique to this particular infection.
Attackers can modify files, rebuild payloads, change URLs, or generate new artifacts.
Behavioral detections therefore provide longer-term value.
Detection Opportunities
A strong endpoint detection strategy should watch for combinations such as:
Email client
↓
Browser
↓
ZIP extraction
↓
LNK execution
↓
PowerShell / script interpreter ↓
ADS creation
↓
DLL loading
↓
AutoIt execution
↓
Outbound HTTPS
The chain is considerably more suspicious than any individual process.
Why AutoIt Deserves Attention
AutoIt is a legitimate scripting and automation technology.
That makes it attractive to malware authors.
Security products cannot simply classify every AutoIt component as malicious without risking false positives.
The better question is:
Why is AutoIt executing on this machine, from this directory, immediately after a suspicious LNK file was opened?
Context transforms a legitimate tool into a valuable behavioral indicator.
Detecting Suspicious Execution Locations
The Guildma component was stored under:
C:UsersPublicLibraries.cache
That path deserves attention when an executable or script suddenly appears there.
Defenders can investigate recently created files with PowerShell:
Get-ChildItem "C:\Users\Public\Libraries" -Recurse -Force | Sort-Object LastWriteTime -Descending | Select-Object -First 50 FullName,Length,LastWriteTime
Again, the goal is not to declare every file in that location malicious.
It is to identify unusual files created around the time of the suspected infection.
Geofencing Creates a Blind Spot
Geofencing is especially dangerous for automated security analysis.
A malware sandbox located in the United States may receive a clean Android Studio installer.
A Brazilian researcher using Brazilian Portuguese Windows settings may receive the actual malware.
This difference can lead analysts to incorrectly conclude that the URL is harmless.
Security testing therefore needs to account for:
Geographic origin
Browser language
Operating-system language
Regional settings
User-agent characteristics
Cookies and session state
Network reputation
Threat Intelligence Must Include Context
Indicators such as domains and hashes remain useful, but they should be connected to the attack chain.
For example:
Malicious domain
+
Brazilian Portuguese phishing
+
ZIP attachment/download +
LNK execution
+
NTFS ADS creation
+
AutoIt
+
Guildma behavior
Together, these indicators form a much stronger detection model.
The Importance of Email Security
Email gateways should inspect links even when the message contains no traditional attachment.
A link that redirects through multiple services, uses unusual infrastructure, or behaves differently according to geography should receive additional scrutiny.
URL rewriting and sandboxing can also help, although geofenced campaigns demonstrate why a single sandbox location may not be enough.
Endpoint Detection Is the Last Line of Defense
Even if the phishing message gets through, the endpoint can still stop the attack.
A modern EDR platform should be capable of identifying suspicious relationships between:
Outlook/Browser → LNK → DLL → AutoIt → Network
The relationship is more important than any individual filename.
This is particularly valuable against constantly changing malware samples.
Network Monitoring Still Matters
Encrypted HTTPS traffic does not make network detection impossible.
Defenders can still monitor:
Newly observed domains
Rare destinations
DNS anomalies
Unusual cloud-hosted endpoints
Suspicious connection timing
Beacon-like communication
Processes responsible for network connections
TLS encryption hides content, but it does not hide every useful signal.
What Undercode Say:
A Familiar Malware Family With a Modern Delivery Strategy
Guildma is not a new name in cybersecurity.
What is interesting here is how an established malware family continues to benefit from modern delivery techniques.
The attackers do not need to reinvent malware if they can reinvent how victims encounter it.
That is exactly what this campaign demonstrates.
Phishing Remains Extremely Effective
The email is simple.
The social engineering is simple.
The technology behind the payload is considerably more complicated.
That contrast tells us something important about modern cybercrime.
Attackers can spend their technical resources making the delivery chain invisible while relying on ordinary human behavior to initiate the compromise.
Geofencing Is Becoming More Important
Security researchers increasingly have to consider where their analysis environment is located.
A malicious server can behave differently in Brazil, the United States, Europe, or Asia.
That makes geographic diversity valuable in threat research.
Language Can Become a Security Signal
The requirement for Brazilian Portuguese settings is particularly notable.
Language configuration is normally treated as a user-experience setting.
In this campaign, it became part of the attacker’s decision-making process.
Security systems should therefore understand that locale information can influence malware delivery.
Alternate Data Streams Deserve More Attention
NTFS alternate data streams remain relatively obscure outside Windows security and forensic circles.
That makes them useful to attackers.
A file can look harmless while carrying additional data that is not immediately visible through conventional browsing.
This is another reason endpoint telemetry needs to capture file-system behavior rather than relying exclusively on file extensions.
Legitimate Tools Can Become Attack Components
The
Attackers frequently abuse legitimate interpreters, scripting engines, cloud services, and development platforms.
The technology itself is not necessarily malicious.
The context is what matters.
Cloud Hosting Complicates Blocking
An Azure-hosted endpoint can make blanket blocking impractical.
Enterprises depend heavily on cloud platforms.
Therefore, security teams increasingly need identity, behavior, reputation, and process-level visibility rather than simple provider-based blocking.
HTTPS Is Not a Free Pass
Attackers routinely use HTTPS because it provides encryption.
But encryption does not erase metadata.
Organizations can still detect unusual destinations, processes, timing, DNS activity, and endpoint behavior.
Hashes Have a Short Shelf Life
The hashes published from this investigation are valuable.
But defenders should not assume that blocking those four files will permanently stop the campaign.
A rebuilt sample produces a new hash.
A new domain can replace an old one.
A modified shortcut can evade a simple signature.
Behavioral Detection Has More Staying Power
The strongest defensive lesson is the attack sequence itself.
A suspicious LNK launching code that creates an ADS, loads a DLL, executes AutoIt, and establishes outbound connections is highly unusual.
That behavioral pattern can remain detectable even after individual indicators change.
The Email Subject Was Carefully Engineered
The use of a “final contract” theme is psychologically effective.
Words suggesting completion, approval, signatures, payments, or legal obligations create pressure.
Victims may feel they need to act immediately.
That urgency reduces the likelihood that they will carefully inspect the sender or URL.
Brazil Was Not an Accidental Choice
The Portuguese lure, regional settings, and geographic filtering all point toward deliberate targeting.
This appears designed to make the campaign more relevant to Brazilian users while making analysis outside Brazil harder.
That is a sophisticated combination of social engineering and technical evasion.
Security Teams Should Think Like the Attacker
Instead of asking:
“Is this file malicious?”
defenders should ask:
“Why did this file appear here, who launched it, what did it launch next, and where did it communicate?”
That approach provides much more context.
Malware Analysis Is Becoming More Environmental
Traditional analysis often focuses on the binary itself.
Modern campaigns increasingly require analysis of the environment surrounding the binary.
Country.
Language.
Locale.
Browser.
Operating system.
User behavior.
Network identity.
All of these can affect what payload a victim receives.
Sandboxes Need Diversity
A single sandbox configuration cannot reliably represent the entire internet.
Threat actors know this.
They can test whether a visitor looks like a researcher, automated scanner, or real victim.
Organizations conducting malware analysis should therefore consider multiple geographic and system profiles when investigating suspicious infrastructure.
The Benign Payload Is Part of the Deception
Returning a legitimate Android Studio installer is particularly clever.
It gives the attacker plausible deniability.
An investigator may test the URL, download the installer, see nothing malicious, and move on.
The infrastructure therefore becomes deceptive before the malware even reaches the endpoint.
Cybersecurity Is Increasingly About Correlation
No single indicator tells the entire story.
The email alone looks suspicious.
The domain alone looks suspicious.
The ZIP alone looks suspicious.
The LNK alone looks suspicious.
The ADS alone looks suspicious.
AutoIt alone is legitimate.
HTTPS alone is normal.
But put everything together and the picture becomes unmistakable.
Detection Engineering Should Follow the Chain
The most useful detections should therefore connect events.
For example:
Browser download → LNK creation → LNK execution → unusual file creation → ADS activity → AutoIt process → external connection
That sequence is far more powerful than a static blacklist.
Users Still Need Training
Technical defenses cannot eliminate every phishing message.
Employees should be trained to question unexpected contract notifications, especially when the message creates urgency.
The safest response to an unexpected digital-signature request is to verify it through an independently known channel.
Incident Response Must Move Quickly
Once a suspicious LNK has been executed, defenders should assume that additional payloads may already have been retrieved.
The machine should be isolated according to the organization’s incident-response procedures.
Investigators should preserve volatile and disk evidence before deleting artifacts.
Persistence Changes the Risk
The presence of a persistent Guildma component means that simply deleting the original ZIP archive is not enough.
The investigator must determine how persistence was established and whether additional accounts, credentials, or systems were affected.
Credential Theft Is the Larger Concern
Guildma’s presence should raise concerns beyond the initial endpoint.
If credentials or sensitive browser information were exposed, the compromise may continue even after the malware is removed.
Password resets, token invalidation, session revocation, and account monitoring may therefore become necessary depending on the evidence.
Threat Actors Reuse Successful Ideas
The specific infrastructure will eventually disappear.
The delivery concepts are more durable.
Geofencing.
Locale checks.
LNK files.
Alternate data streams.
Legitimate cloud hosting.
AutoIt.
Encrypted communications.
These techniques can easily appear in future campaigns involving completely different malware families.
Security Research Needs to Keep Pace
The infection analyzed on August 31, 2026, is a reminder that malware research cannot stop at identifying the final payload.
Understanding how the attacker made the payload difficult to observe can be even more valuable.
The Biggest Lesson
The most important lesson is simple:
Malware does not have to look malicious at every stage.
A harmless-looking email can lead to a harmless-looking ZIP, which launches a harmless-looking shortcut, which stores a seemingly harmless DLL, which invokes a legitimate scripting technology, ultimately delivering a dangerous malware family.
That is the modern attack chain.
✅ Guildma Is Also Known as Astaroth
Guildma is commonly referred to as Astaroth in cybersecurity reporting and research.
The malware family has a long association with Brazilian-targeted campaigns and has historically been used for information and credential theft.
✅ The Infection Used NTFS Alternate Data Streams
The analysis specifically identifies an executable DLL stored in an alternate data stream under the Windows temporary directory.
That is a legitimate Windows/NTFS capability that can also be abused to conceal data.
✅ The Campaign Used Environmental Filtering
The infection analysis reports both geographic filtering for Brazil and requirements involving Brazilian Portuguese language and regional settings.
This makes the campaign significantly harder to reproduce from generic security-analysis environments.
❌ The Individual Hashes Should Not Be Treated as Permanent Signatures
The listed SHA-256 values are useful indicators for this observed infection.
However, malware operators can rebuild payloads and produce entirely different hashes.
Behavioral and infrastructure-based detections should therefore complement hash-based blocking.
✅ HTTPS Traffic Does Not Mean the Destination Is Safe
The observed malicious infrastructure communicated over TCP port 443.
HTTPS provides encryption, but it does not inherently establish that the destination or process communicating with it is trustworthy.
Prediction
(+1) Regionalized Malware Campaigns Will Become More Common
Attackers are likely to increase their use of geographic and language-based filtering because it makes campaigns harder for researchers and automated security systems to analyze.
A malicious server can effectively decide which visitors deserve the real payload.
(+1) Locale-Aware Security Testing Will Become Standard
Security laboratories will increasingly need to reproduce victim environments more accurately.
That means testing different countries, languages, time zones, browser configurations, and operating-system settings.
(+1) Behavioral Detection Will Outperform Simple Hash Blocking
As malware becomes more modular and frequently rebuilt, static hashes will lose effectiveness as the primary detection method.
Security teams will increasingly focus on suspicious process chains and abnormal file-system behavior.
(+1) Legitimate Platforms Will Continue Appearing in Attack Chains
Cloud hosting providers, code repositories, messaging platforms, and scripting frameworks will continue to be abused because completely blocking them is unrealistic.
The future of detection will therefore depend heavily on context.
(-1) Phishing Will Remain a Major Initial-Access Problem
Despite better security technology, convincing business-themed emails will continue to exploit human trust.
Contract, invoice, payment, document-signing, and account-verification lures are unlikely to disappear.
(-1) Automated Malware Analysis Will Face More Evasion
Campaigns that require a particular country and language configuration can already evade simplistic sandboxing.
As environmental fingerprinting becomes more sophisticated, poorly configured automated analysis systems will increasingly return false negatives.
(+1) The Guildma Campaign Is a Warning Rather Than an Endpoint
The most valuable takeaway from this infection is not the specific ZIP file or domain.
It is the architecture of the attack.
Social engineering + environmental filtering + living-off-legitimate technology + hidden file storage + staged execution + encrypted communications
That combination is likely to influence future malware campaigns long after these specific indicators have disappeared.
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References:
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