KnowBe4 ThreatLabs has identified and analyzed a sophisticated cross-platform phishing campaign that utilizes Telegram as its primary exfiltration channel.
The campaign uses a combination of security-themed phishing emails, branded phishing websites to harvest credentials, and Telegram bots to exfiltrate data.
Based on our technical analysis of the campaign, we believe this attack is sold as part of a phishing-as-a-service kit that enables different threat actors to leverage the same infrastructure, meaning it has the potential to become a widespread threat. Additionally, as the credential harvesting websites are platform agnostic (impersonating several well-known brands), we understand the cybercriminals’ goal is to harvest the maximum number of credentials versus targeting specific services.
Phishing Attack Summary
Vector and type: Email phishing
Primary techniques: Phishing hyperlinks, impersonation, automated exfiltration
Targets: Global
Platform: Microsoft 365, Google
Bypassed native and SEG detection: Yes
The campaign is conducted over three stages. The first two mimic what we’d expect to see in a typical credential harvesting attack - with some additional flairs to make it simultaneously more convincing to its victims and more resilient against traditional technical measures to block the attacks.
In the first stage, targets receive an initial phishing email that focuses on a cybersecurity-related topic, such as a suspicious log in attempt.
Next, when they click the hyperlink within the phishing email or attachment, the target is taken to a credential harvesting website that dynamically impersonates a brand associated with their organization. On the backend, the campaign leverages distributed hosting across multiple providers for these phishing websites, with rapid domain rotation, which makes the infrastructure more resilient against blocklists.
In the final stage, harvested credentials are transmitted directly to threat actor-controlled Telegram bots using configurable tokens and chat IDs. This provides real-time credential delivery while allowing cybercriminals to hide behind Telegram’s legitimate infrastructure to initiate account takeover (ATO) within seconds of the credentials being received.
Security-themed Phishing Emails Use Victims’ Best Intentions Against Them
The initial phishing emails center on cybersecurity themes, such as unauthorized access attempts and settings updates, to socially engineer their targets. Communications on security topics can engineer a sense of legitimacy and a corresponding level of trust in their targets. Additionally, the topics can also create a sense of urgency, with people acting quickly when they believe their accounts - and data - could potentially be at risk.
As seen in the example below, the text is further designed to manipulate the victims into taking swift action, with threats that features or access may be switched off.
Phishing email sent as part of credential harvesting campaign, reported via KnowBe4 PhishER
As the emails were provided as part of a phishing kit, the sending mechanism varied depending on the cybercriminal who was launching the attack. We observed attacks coming from compromised legitimate email addresses, which makes it easier for attacks to bypass reputation-based detection, as well as from spoofed domains. Both tactics can also lull victims into a false sense of security, believing they are communicating with a trusted sender.
Some of the subject lines we observed in this campaign included:
- Email Suspension Notice
- Account Suspension Notice
- Review deactivation for
- Unusual Sign-In Detected for
- Email Suspension Notice for
The phishing hyperlinks are embedded into the emails (as above) or contained with PDF attachments. In either scenario, the hyperlink leads to a credential-harvesting webpage.
Dynamically Branded Phishing Webpages
In an attempt to harvest the maximum number of credentials, the webpages use a dynamic branding mechanism tailored to the target organization. The page impersonates well-known brands such as Microsoft, Google, and Adobe, alongside others, that are connected to the target victim and prefills their email address.
Credential harvesting website that impersonates Microsoft, with source code demonstrating dynamic branding tailored to the recipient, prepopulated email address, and multiple password harvesting attempts.
The source code for these pages reveals a sophisticated dynamic branding system that is designed to create a tailored experience based on the recipient’s experience. The kit employs a JavaScript initialization routine that extracts organizational information from the victim's email address to customize the login portal's appearance.
As shown in the screenshot below, the attack automatically extracts domain information, retrieves organizational branding elements, and dynamically adjusts the interface to match the victim’s expectations.
Source code for phishing webpage revealing how JavaScript is used to dynamically personalize the page to the recipient based on (1) their organization; and (2) their preferred language.
The kit also implements an advanced browser detection system through the GetBrowserandLanguage() function that dynamically adjusts how the content is presented based on the victim's browser language settings. This localization mechanism presents authentication forms, security warnings, and instructional text in the victim’s preferred language, significantly increasing the attack’s appearance of legitimacy.
This tailored experience is designed to lure the victim into a false sense of security: they will likely be familiar with custom branding and form autofills, meaning they’re less likely to spot that they’re entering their credentials into a phishing website. Additionally, prefilled emails on forms removes once less barrier to completion, giving the target less time to consider their actions, and also ensures the cybercriminals are sourcing work log ins.
Credential Exfiltration via Telegram Bots
The most distinctive element of this campaign is its sophisticated Telegram-based exfiltration architecture. Immediately after a target enters their credentials into the phishing website, the attack implements an “Instant Session Capturing” system that transmits the data to the cybercriminals via Telegram’s bot API framework.
This real-time exfiltration provides the attackers’ with a significant operational security advantage. When credentials are submitted, the phishing kit bundles the complete authentication package (including email addresses, passwords, and geo and IP information) and delivers them directly to the threat actor's mobile device through Telegram's notification system. This creates a near-instantaneous alert that enables attackers to operationalize compromised credentials within seconds.
The technical implementation leverages Telegram's robust API infrastructure to create a resilient command and control channel that benefits from Telegram’s legitimate infrastructure and encryption capabilities.
Screenshot of phishing website source code revealing how cybercriminals(1) exfiltrate credentials via (2 and 3) Telegram bots.
The exploitation of a legitimate service as part of a phishing attack is a well-established tactic - and our Threat Lab team has analyzed other recent examples involving Microsoft, Google and QuickBooks services.
Detecting Credential-harvesting Phishing Attacks
As detailed, the campaign contains numerous elements to help it evade technical detection and appear more convincing to targets. Due to its widespread adoption, bypassing traditional signature-based and reputation-based detection is simply “part of the job” for cybercriminals - so measures such as sending from compromised accounts, as seen in some of the attacks we analyzed from this campaign, are increasingly common. Additionally, social engineering elements such as using cybersecurity related topics and dynamically branded phishing websites increases the likelihood that a target will fall victim.
Increasingly, organizations are turning to Integrated Cloud Email Security products (such as KnowBe4 Defend) that leverage AI to detect advanced phishing threats and prevent employees from interacting with malicious hyperlinks and attachments. Additionally, threat-based awareness and training, including flipping real phishing emails into training simulations (e.g. via KnowBe4 PhishER), educates employees on the phishing attacks they’re most likely to face.
KnowBe4 Threat Lab
KnowBe4 Threat Lab specializes in researching email threats and phishing attacks, utilizing a combination of expert analysis and crowdsourced intelligence.
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