Muck Stealer Malware Used Alongside Phishing in New Attack Waves
Summary:
Threat actors are increasingly combining credential phishing and malware delivery in a single attack, which is not typically the case. This new approach, observed in several recent high-impact campaigns, allows attackers to bypass security measures that may be strong in one area but weaker in another. Four distinct methods for this combined attack have been identified by Cofense. One of the campaigns, "Hosted PDF With a Link to Credential Phishing or Malware," is ongoing and had a particularly large volume of attacks. files[.]fm was utilized for hosting PDF malware in some of the campaigns. The malware most commonly delivered by these methods is ConnectWise RAT.
Cofense shares several specific examples that illustrate this trend. A campaign spoofing the American Social Security Agency delivered ConnectWise RAT, followed by a credential phishing page that immediately collected detailed personal information, including Social Security Numbers and phone carrier PINs, which the malware itself might not have been able to obtain. Another campaign used a hosted PDF to link to both a credential phishing page and a malware download. A July 2025 campaign varied its payload based on the user's browser, delivering Windows-specific malware (SimpleHelp RAT), an Android APK, or an iOS-targeted credential phishing page depending on the victim's platform. A January 2025 campaign first collected credentials via a phishing page and then downloaded a VBS script that executed a customized Information Stealer, effectively "doubling up" on Microsoft Office credential collection. The final campaign outlined in this article, a December 2024 campaign, used a malicious downloader to deliver Muck Stealer, which then launched an HTML file for credential phishing and disguising the malware's activity. Combining these methods allows threat actors to collect more comprehensive information and conduct longer-term reconnaissance on the infected host for additional information.
Security Officer Comments:
The convergence of credential phishing techniques and malware delivery techniques in these attacks represents a notable shift in cybercriminal attack methodology, as it's often the case that these kinds of attacks are mutually exclusive. This strategy indicates a shift by threat actors toward a more resilient and multi-pronged approach to credential exfiltration, along with other sensitive data. By not relying on a single method, they are hedging their bets against targeted security tooling employed by their victims’ organizations. This trend necessitates that organizations adopt a comprehensive security posture, ensuring that both their credential phishing and malware detection capabilities are effectively integrated. The inclusion of reconnaissance capabilities and the specific targeting of sensitive data like Social Security Numbers highlights a potentially sophisticated move toward lateral movement for high-value attacks and identity fraud in future operations like remote IT worker fraud.
Suggested Corrections:
Although not every end user has access to advanced anti-phUsers should always be cautious of individuals or organizations that ask for personal information. Most companies will not ask for sensitive data from their customers. If in doubt, users should verify with the company itself to avoid any potential issues.
Users should always take a close look at the sender’s display name when checking the legitimacy of an email. Most companies use a single domain for their URLs and emails, so a message that originates from a different domain is a red flag.
As a general rule, users should not click links or download files even if they come from seemingly “trustworthy” sources.
Check for mismatched URLs. While an embedded URL might seem perfectly valid, hovering above it might show a different web address. In fact, users should avoid clicking links in emails unless they are certain that it is a legitimate link.
Users should always be on the lookout for any grammatical errors and spelling mistakes. Legitimate companies will often employ proofreaders and editors who ensure that the materials they send out are error-free.
Users should not be frightened or intimidated by messages that have an alarmist tone. They should double check with the company if they are uncertain about the status of their accounts.
Phishing emails are designed to be sent to a large number of people, so they need to be as impersonal as possible. Users should check whether the message contains a generic subject and greeting, as this can be a sign of a phishing attempt.
ishing software, they can still use the built-in protection of their email clients to filter messages. One example is setting the email client to block all images unless approved.
Legitimate companies will never send confirmation emails unless there are specific reasons for doing so. In fact, most companies will avoid sending unsolicited messages unless it’s for company updates, newsletters, or advertising purposes.
Users should always take the context of an email or message into account. For example, most online accounts do away with viewable member numbers, so users should be wary if they receive emails containing a “member number” for services that generally don’t use them.
It is important to take note of unusual information in the text of the message. Any mentions of operating systems and software that are not typically used by consumers can often be indicators of a phishing attempt.
If it seems suspicious, it probably is. Users should always err on the side of caution when it comes to sending out personally identifiable information through messages and emails.
Link(s):
https://hackread.com/muck-stealer-malware-phishing-new-attack-waves/
https://cofense.com/blog/dual-threat-threat-actors-combine-credential-phishing-and-malware
Threat actors are increasingly combining credential phishing and malware delivery in a single attack, which is not typically the case. This new approach, observed in several recent high-impact campaigns, allows attackers to bypass security measures that may be strong in one area but weaker in another. Four distinct methods for this combined attack have been identified by Cofense. One of the campaigns, "Hosted PDF With a Link to Credential Phishing or Malware," is ongoing and had a particularly large volume of attacks. files[.]fm was utilized for hosting PDF malware in some of the campaigns. The malware most commonly delivered by these methods is ConnectWise RAT.
Cofense shares several specific examples that illustrate this trend. A campaign spoofing the American Social Security Agency delivered ConnectWise RAT, followed by a credential phishing page that immediately collected detailed personal information, including Social Security Numbers and phone carrier PINs, which the malware itself might not have been able to obtain. Another campaign used a hosted PDF to link to both a credential phishing page and a malware download. A July 2025 campaign varied its payload based on the user's browser, delivering Windows-specific malware (SimpleHelp RAT), an Android APK, or an iOS-targeted credential phishing page depending on the victim's platform. A January 2025 campaign first collected credentials via a phishing page and then downloaded a VBS script that executed a customized Information Stealer, effectively "doubling up" on Microsoft Office credential collection. The final campaign outlined in this article, a December 2024 campaign, used a malicious downloader to deliver Muck Stealer, which then launched an HTML file for credential phishing and disguising the malware's activity. Combining these methods allows threat actors to collect more comprehensive information and conduct longer-term reconnaissance on the infected host for additional information.
Security Officer Comments:
The convergence of credential phishing techniques and malware delivery techniques in these attacks represents a notable shift in cybercriminal attack methodology, as it's often the case that these kinds of attacks are mutually exclusive. This strategy indicates a shift by threat actors toward a more resilient and multi-pronged approach to credential exfiltration, along with other sensitive data. By not relying on a single method, they are hedging their bets against targeted security tooling employed by their victims’ organizations. This trend necessitates that organizations adopt a comprehensive security posture, ensuring that both their credential phishing and malware detection capabilities are effectively integrated. The inclusion of reconnaissance capabilities and the specific targeting of sensitive data like Social Security Numbers highlights a potentially sophisticated move toward lateral movement for high-value attacks and identity fraud in future operations like remote IT worker fraud.
Suggested Corrections:
Although not every end user has access to advanced anti-phUsers should always be cautious of individuals or organizations that ask for personal information. Most companies will not ask for sensitive data from their customers. If in doubt, users should verify with the company itself to avoid any potential issues.
Users should always take a close look at the sender’s display name when checking the legitimacy of an email. Most companies use a single domain for their URLs and emails, so a message that originates from a different domain is a red flag.
As a general rule, users should not click links or download files even if they come from seemingly “trustworthy” sources.
Check for mismatched URLs. While an embedded URL might seem perfectly valid, hovering above it might show a different web address. In fact, users should avoid clicking links in emails unless they are certain that it is a legitimate link.
Users should always be on the lookout for any grammatical errors and spelling mistakes. Legitimate companies will often employ proofreaders and editors who ensure that the materials they send out are error-free.
Users should not be frightened or intimidated by messages that have an alarmist tone. They should double check with the company if they are uncertain about the status of their accounts.
Phishing emails are designed to be sent to a large number of people, so they need to be as impersonal as possible. Users should check whether the message contains a generic subject and greeting, as this can be a sign of a phishing attempt.
ishing software, they can still use the built-in protection of their email clients to filter messages. One example is setting the email client to block all images unless approved.
Legitimate companies will never send confirmation emails unless there are specific reasons for doing so. In fact, most companies will avoid sending unsolicited messages unless it’s for company updates, newsletters, or advertising purposes.
Users should always take the context of an email or message into account. For example, most online accounts do away with viewable member numbers, so users should be wary if they receive emails containing a “member number” for services that generally don’t use them.
It is important to take note of unusual information in the text of the message. Any mentions of operating systems and software that are not typically used by consumers can often be indicators of a phishing attempt.
If it seems suspicious, it probably is. Users should always err on the side of caution when it comes to sending out personally identifiable information through messages and emails.
Link(s):
https://hackread.com/muck-stealer-malware-phishing-new-attack-waves/
https://cofense.com/blog/dual-threat-threat-actors-combine-credential-phishing-and-malware