{ "id": "425256f9-326f-4f37-99ec-67ba0f2493b2", "created_at": "2026-04-06T01:29:32.471529Z", "updated_at": "2026-04-10T03:31:13.46502Z", "deleted_at": null, "sha1_hash": "9d984e4a349304d5241f00ef7bea4afe618aac99", "title": "Targeted Attacks Abusing Google Cloud Platform Open Redirection", "llm_title": "", "authors": "", "file_creation_date": "0001-01-01T00:00:00Z", "file_modification_date": "0001-01-01T00:00:00Z", "file_size": 79800, "plain_text": "Targeted Attacks Abusing Google Cloud Platform Open\r\nRedirection\r\nBy Ashwin Vamshi\r\nPublished: 2019-01-24 · Archived: 2026-04-06 00:53:27 UTC\r\nNetskope Threat Research Labs detected several targeted themed attacks across 42 customer instances mostly in\r\nthe banking and finance sector. The threat actors involved in these attacks used the App Engine Google Cloud\r\ncomputing platform (GCP) to deliver malware via PDF decoys. After further research, we confirmed evidence of\r\nthese attacks targeting governments and financial firms worldwide. Several decoys were likely related to an\r\ninfamous threat actor group named ‘Cobalt Strike’.\r\nThe attacks were carried out by abusing the GCP URL redirection in PDF decoys and redirecting to the malicious\r\nURL hosting the malicious payload. This targeted attack is more convincing than the traditional attacks because\r\nthe URL hosting the malware points the host URL to Google App Engine, thus making the victim believe the file\r\nis delivered from a trusted source like Google.\r\nThis post describes our discovery and analysis of the Google App Engine URL Redirection abuse, the threat actor\r\nresponsible, and the malware abusing this feature. We conclude with some recommendations to help protect and\r\nremediate such threats.\r\nNetskope Detection\r\nNetskope Advanced Threat Protection detects the targeted decoy we identified as PDF_Phish.Gen.\r\nDisclosure\r\nNetskope reported this abuse to Google on 10 January 2019. The open redirector exists by design. \r\nDiscovery\r\nEarly this year, Netskope’s telemetry identified common detections across 42 customers in the banking and\r\nfinance sector. All these were eml files that carried an .eml extension and had the same detection name, triggering\r\nalerts in our Outbreak Detection Systems. After investigation, we confirmed that the detections were triggered in\r\nthe attachments of the eml files.\r\nLeveraging our Netskope Discovery and Netskope Active Introspection Alerts platforms, we discovered these\r\nattacks were abusing Google App Engine on the Google Cloud Platform (GCP) as a bait to deliver malware.\r\nPDF Decoys – Delivery\r\nhttps://www.netskope.com/blog/targeted-attacks-abusing-google-cloud-platform-open-redirection\r\nPage 1 of 10\n\nThe PDF decoys traditionally arrive as email attachments to victims. The emails are crafted to contain legitimate\r\ncontent and deliver the malware from allow listed sources. Often, such attachments are saved to cloud storage\r\nservices, like Google Drive. Sharing these documents with other users can result in the occurrence of a secondary\r\npropagation vector like the CloudPhishing Fan-out Effect. In this case, the email file containing the decoy\r\ndocument was detected by Advanced Threat Protection and the potential fan-out was prevented.\r\nGCP App Engine URL Redirection – Decoys\r\nThis targeted attack is more convincing than the traditional attacks because the decoy deceives the victim with a\r\nGoogleApp Engine URL which is abused to redirect the victim to the malware. As the payload seems to be\r\noriginating from a trusted source, the chance of falling victim to such attacks is very likely.\r\nThe themed PDF decoys we observed using GCP App Engine URL Redirection is shown in Figure 1.\r\nFigure 1:  PDF decoys using GCP App Engine URL Redirection.\r\nMost of the PDF’s we observed were created using Adobe Acrobat 18.0. They contained the malicious URL in a\r\ncompressed form in the PDF stream using Flat Decode (Filter/FlateDecode). Similarly, all the decoys used HTTPS\r\nhttps://www.netskope.com/blog/targeted-attacks-abusing-google-cloud-platform-open-redirection\r\nPage 2 of 10\n\nURLs for delivering the payload.\r\nGCP App Engine URL Redirection – Overview\r\nThe URL redirection case with Google App Engine falls under the category of Unvalidated Redirects and\r\nForwards as per the Open Web Application Security Project (OWASP).\r\n Some of the URLs we observed from the PDF decoys using this technique are shown below\r\nhttps://appengine.google[.]com/_ah/logout?continue=https%3A%2F%2Ftransef[.]biz%2FDoc102018.doc\r\nhttps://appengine.google[.]com/_ah/logout?continue=https%3A%2F%2Fswptransaction-scan2034.s3.ca-central-1.amazonaws[.]com%2FDoc102018.doc\r\nFor a better understanding and illustration, we have taken the below URL as an example\r\nhttps://appengine.google[.]com/_ah/logout?continue=https%3A%2F%2Ftransef[.]biz%2FDoc102018.doc\r\nThe packet capture illustrating this activity is shown in Figure 2.\r\nhttps://www.netskope.com/blog/targeted-attacks-abusing-google-cloud-platform-open-redirection\r\nPage 3 of 10\n\nFigure 2: GCP App Engine URL Redirection packet capture\r\nFigure 2 illustrates that once the URL is accessed, the user is logged out from appengine.google.com and a\r\nresponse status code ‘302’ is generated for URL redirection. As this action gets executed, the user is inturn\r\nredirected to google.com/url using the query “?continue=”.  Using this redirection logic, the destination landing\r\npage is reached, and in this case, Doc102018.doc is downloaded to the victim’s machine.\r\nUsing the same logic in the query, we tried the same approach with GCP App Engine URL as follows:\r\nhttps://accounts.google.com/Logout?continue=https://appengine.google.com/_ah/logout?\r\ncontinue=https%3A%2F%2Ftransef[.]biz%2FDoc102018.doc\r\nhttps://google.com/accounts/Logout?continue=https://appengine.google.com/_ah/logout?\r\ncontinue=https%3A%2F%2Ftransef[.]biz%2FDoc102018.doc\r\nIn all these cases, the GCP App Engine application successfully validated the redirection and delivered the\r\npayload to the victims machine.\r\nSince the appended URL is an unvalidated redirect, the threat actors abused this feature by redirecting a victim to\r\na malicious appended URL hosting the malicious payload.\r\nPDF Decoys – Default Allow policy\r\nGenerally, PDF readers prompt a security warning to the user when the document connects to a website. Once\r\n“remember this action for this site” is checked for a domain, this feature allows any URL within the domain\r\nwithout any prompt.\r\nThe activity illustrating this action is shown in Figure 3.\r\nhttps://www.netskope.com/blog/targeted-attacks-abusing-google-cloud-platform-open-redirection\r\nPage 4 of 10\n\nFigure 3: PDF decoy abusing GCP App Engine URL Redirection\r\nBy taking advantage of the “default allow” action in popular PDF readers, the attacker can easily deploy multiple\r\nattacks without getting the security warning after the first alert. It is also possible that appengine.google.com is\r\nallow listed by the administrators for legitimate reasons. It also only warns the user that it is trying to connect to\r\nappengine.google.com, which looks benign at face value. \r\nMalware using GCP URL Redirection\r\nAll the PDFs involved in this attack downloaded Microsoft Word documents with obfuscated macro code or PDF\r\ndocuments as the second stage payload.\r\nThe PDF decoy detected in our customer instances downloaded a word document named “Doc102018.doc”\r\ncontaining obfuscated macro code. This document was downloaded from the URL https://transef[.]biz.\r\nOn execution, the victim is presented with a message to enable editing and content mode to view the document as\r\nshown in Figure 4.\r\nhttps://www.netskope.com/blog/targeted-attacks-abusing-google-cloud-platform-open-redirection\r\nPage 5 of 10\n\nFigure 4: Message to enable editing and content mode to view the document.\r\nOn enabling the option, the macro gets executed and downloads another stage payload from transef[.]biz/fr.txt.\r\nThe stage payloads are often used by threat actors to ensure a smoother transition and to make an attack harder to\r\ndetect, investigate and mitigate\r\nfr.txt is detonated using Microsoft Connection Manager Profile Installer (csmtp.exe) from the location,\r\n%Appdata%\\Roaming\\Microsoft\\26117.txt as an INF file shown in Figure 5.\r\nhttps://www.netskope.com/blog/targeted-attacks-abusing-google-cloud-platform-open-redirection\r\nPage 6 of 10\n\nFigure 5:  csmtp.exe executing %Appdata%\\Roaming\\Microsoft\\26117.txt\r\nThis technique resembles to the “Squiblydoo” technique, detailed in our previous research of ShortJSRAT.\r\nSquiblydoo is a technique wherein malicious scriptlets are loaded using native Windows applications. This\r\nbypasses application allow listing solutions like Windows Applocker, which allow only approved applications to\r\nload and execute.\r\nAt the time of analysis, the next stage payload “fr.txt” was down and not serving any payload. Though the payload\r\nwas down, we leveraged our Netskope Threat Intelligence to attribute these attacks to an infamous threat actor\r\ngroup named ‘Cobalt Strike’, detailed in an research article by Cisco Talos.\r\nThe ‘Cobalt Strike group’ has a reputation of targeting financial and Banking firms using several Tactics,\r\nTechniques and Procedures   (TTPs), using malware like the high-profile Carbanak malware. This group is also\r\nknown to heavily use a the software Cobalt Strike in its arsenal. The Cobalt Strike software is a white-hat tool for\r\nperforming security assessments that replicates the tactics and techniques of an advanced adversary in a network.\r\nThough the mastermind of the group was arrested on March 26th, 2018 by Europol, there are still some targeted\r\nattacks executed by the group. Based on the timeline of the emails sent to the potential targets we expect the group\r\nhttps://www.netskope.com/blog/targeted-attacks-abusing-google-cloud-platform-open-redirection\r\nPage 7 of 10\n\nto be actively carrying out attacks.\r\nPDF Decoys – Emails and potential targets\r\nBased on our threat intelligence research, more than 20 other banking, government and financial institutions were\r\ntargeted with the same attack via phishing emails sent by the attackers posing as legitimate customers of those\r\ninstitutions. There were no discernable geographic patterns in organizations targeted — the targets were\r\ndistributed worldwide. Some of the targets include:\r\nMetrobank Philippines\r\nPrime Commercial Bank Ltd, Nepal\r\nBancNet Online\r\nBanque du Caire, or “Bank of Cairo”\r\nItaú International Investment\r\nMinistry of External Affairs, India\r\nYapıKredi\r\nBank of Alexandria\r\nOmniPay, Asia\r\nBancosol\r\nTravelex foreign exchange business\r\nStandard Bank, South Africa\r\nMCB: Mauritius Commercial Bank\r\nExtraco Bank\r\nBank Albilad\r\nAccuity\r\nSKB Bank, Russia\r\nRGS Bank, Russia\r\nSome of the most commonly used email domains and email address by the threat actor are as follows\r\npace.edu\r\njk01814n@pace.edu\r\nulaval.ca\r\nbenoit.filion.2@ulaval.ca\r\nalexandre.custeau.1@ulaval.ca\r\ndominique.denis-berube.1@ulaval.ca\r\nmetacase.eu\r\nhelpdesk@metacase.eu\r\nivywise.com\r\nadrienne@ivywise.com\r\nebf.eu.com\r\ninfo@ebf.eu.com\r\nsec@ebf.eu.com\r\nr.evans@ebf.eu.com\r\nhttps://www.netskope.com/blog/targeted-attacks-abusing-google-cloud-platform-open-redirection\r\nPage 8 of 10\n\nAlthough the emails were sent to the targets from the threat actor, there is a possibility that these email address\r\nmight be a spoofed with a forged sender.\r\nAn example of emails sent from the email address jk01814n@pace.edu, to a list of 6 potential targets as shown in\r\nFigure 6.\r\nFigure 6: Emails sent to potential targets from jk01814n@pace.edu\r\nConclusion\r\nOur research initially started with the discovery of GCP URL abuse triggering detections across 42 customers in\r\nthe banking and finance sector. Our in-house systems and Netskope Threat Intelligence Framework connected the\r\ndots and seamlessly aided us in tying the attacks to the infamous ‘Cobalt Strike’ threat actor group.\r\nURL redirection mechanisms / features are widely used and abused by threat actors to deceive victims into\r\nbelieving the malicious file is being delivered from a trusted source. The usage of themed PDF decoys with\r\nenticing emails is a perfect choice since the payload seems to be originating from a trusted source and popular\r\nPDF viewers enable users to easily allow list domains.\r\nhttps://www.netskope.com/blog/targeted-attacks-abusing-google-cloud-platform-open-redirection\r\nPage 9 of 10\n\nUsers can recognize URL redirection abuse by hovering the mouse over all hyperlinks before connecting to the\r\nURL. Enterprises should educate their users to recognize AWS, Azure, and GCP URLs, so they can discern\r\nmalicious sites from official sites.\r\nNetskope Advanced Threat Protection, with its unique cloud vantage point and multi-layered threat detection and\r\nremediation capabilities, offers customers a cloud scale platform that understands, and responds to such attacks,\r\npreventing them from spreading in your cloud environments. \r\nNetskope Threat Research Labs will continue to monitor the developments of ‘Cobalt Strike’ threat actor group.\r\nRecommendations\r\nNetskope recommends the following  to combat cloud-based phishing campaigns:\r\nAlways check the domain of the link. Know the domains typically used when you login to sensitive\r\nservices. Additionally, be able to identify common object store domains. This knowledge will help you\r\ndifferentiate between well-crafted phishing / malware sites and official sites.\r\nDeploy a real-time visibility and control solution to monitor activities across sanctioned and unsanctioned\r\ncloud accounts.\r\nGet comprehensive threat and malware detection for IaaS, SaaS, PaaS, and the web with real-time, multi-layered threat detection and remediation to prevent your organization from unknowingly spreading similar\r\nthreats.\r\nActively track usage of unsanctioned cloud apps and enforce DLP policies to control files and data entering\r\nand leaving your corporate environment\r\nWarn users against opening untrusted attachments, regardless of their extensions or filenames.\r\nWarn users to avoid executing any file unless they are very sure that they are benign.\r\nUn-check the option “Remember this action for this site for all PDF documents” in the PDF reader\r\nsoftware, even if the site appears to be something legitimate, like appengine.google.com\r\nHover your mouse over all hyperlinks to confirm them before clicking on the link.\r\nActively track URL links added to the “Always Allow” list in PDF reader software\r\nKeep systems and antivirus updated with the latest releases and patches.\r\nSource: https://www.netskope.com/blog/targeted-attacks-abusing-google-cloud-platform-open-redirection\r\nhttps://www.netskope.com/blog/targeted-attacks-abusing-google-cloud-platform-open-redirection\r\nPage 10 of 10", "extraction_quality": 1, "language": "EN", "sources": [ "MITRE" ], "references": [ "https://www.netskope.com/blog/targeted-attacks-abusing-google-cloud-platform-open-redirection" ], "report_names": [ "targeted-attacks-abusing-google-cloud-platform-open-redirection" ], "threat_actors": [ { "id": "c9617bb6-45c8-495e-9759-2177e61a8e91", "created_at": "2022-10-25T15:50:23.405039Z", "updated_at": "2026-04-10T02:00:05.387643Z", "deleted_at": null, "main_name": "Carbanak", "aliases": [ "Carbanak", "Anunak" ], "source_name": "MITRE:Carbanak", "tools": [ "Carbanak", "Mimikatz", "PsExec", "netsh" ], "source_id": "MITRE", "reports": null }, { "id": "9de1979b-40fc-44dc-855d-193edda4f3b8", "created_at": "2025-08-07T02:03:24.92723Z", "updated_at": "2026-04-10T02:00:03.755516Z", "deleted_at": null, "main_name": "GOLD LOCUST", "aliases": [ "Anunak", "Carbanak", "Carbon Spider ", "FIN7 ", "Silicon " ], "source_name": "Secureworks:GOLD LOCUST", "tools": [ "Carbanak" ], "source_id": "Secureworks", "reports": null }, { "id": "610a7295-3139-4f34-8cec-b3da40add480", "created_at": "2023-01-06T13:46:38.608142Z", "updated_at": "2026-04-10T02:00:03.03764Z", "deleted_at": null, "main_name": "Cobalt", "aliases": [ "Cobalt Group", "Cobalt Gang", "GOLD KINGSWOOD", "COBALT SPIDER", "G0080", "Mule Libra" ], "source_name": "MISPGALAXY:Cobalt", "tools": [], "source_id": "MISPGALAXY", "reports": null }, { "id": "bb8702c5-52ac-4359-8409-998a7cc3eeaf", "created_at": "2023-01-06T13:46:38.405479Z", "updated_at": "2026-04-10T02:00:02.961112Z", "deleted_at": null, "main_name": "FIN7", "aliases": [ "ATK32", "G0046", "G0008", "Sangria Tempest", "ELBRUS", "GOLD NIAGARA", "Coreid", "Carbanak", "Carbon Spider", "JokerStash", "CARBON SPIDER" ], "source_name": "MISPGALAXY:FIN7", "tools": [], "source_id": "MISPGALAXY", "reports": null }, { "id": "ed3810b7-141a-4ed0-8a01-6a972b80458d", "created_at": "2022-10-25T16:07:23.443259Z", "updated_at": "2026-04-10T02:00:04.602946Z", "deleted_at": null, "main_name": "Carbanak", "aliases": [ "Anunak", "Carbanak", "Carbon Spider", "ELBRUS", "G0008", "Gold Waterfall", "Sangria Tempest" ], "source_name": "ETDA:Carbanak", "tools": [ "AVE_MARIA", "Agentemis", "AmmyyRAT", "Antak", "Anunak", "Ave Maria", "AveMariaRAT", "BABYMETAL", "BIRDDOG", "Backdoor Batel", "Batel", "Bateleur", "BlackMatter", "Boostwrite", "Cain \u0026 Abel", "Carbanak", "Cl0p", "Cobalt Strike", "CobaltStrike", "DNSMessenger", "DNSRat", "DNSbot", "DRIFTPIN", "DarkSide", "FOXGRABBER", "FlawedAmmyy", "HALFBAKED", "JS Flash", "KLRD", "MBR Eraser", "Mimikatz", "Nadrac", "Odinaff", "POWERPIPE", "POWERSOURCE", "PsExec", "SQLRAT", "Sekur", "Sekur RAT", "SocksBot", "SoftPerfect Network Scanner", "Spy.Agent.ORM", "TEXTMATE", "TeamViewer", "TiniMet", "TinyMet", "Toshliph", "VB Flash", "WARPRISM", "avemaria", "cobeacon" ], "source_id": "ETDA", "reports": null }, { "id": "f4f16213-7a22-4527-aecb-b964c64c2c46", "created_at": "2024-06-19T02:03:08.090932Z", "updated_at": "2026-04-10T02:00:03.6289Z", "deleted_at": null, "main_name": "GOLD NIAGARA", "aliases": [ "Calcium ", "Carbanak", "Carbon Spider ", "FIN7 ", "Navigator ", "Sangria Tempest ", "TelePort Crew " ], "source_name": "Secureworks:GOLD NIAGARA", "tools": [ "Bateleur", "Carbanak", "Cobalt Strike", "DICELOADER", "DRIFTPIN", "GGLDR", "GRIFFON", "JSSLoader", "Meterpreter", "OFFTRACK", "PILLOWMINT", "POWERTRASH", "SUPERSOFT", "TAKEOUT", "TinyMet" ], "source_id": "Secureworks", "reports": null } ], "ts_created_at": 1775438972, "ts_updated_at": 1775791873, "ts_creation_date": 0, "ts_modification_date": 0, "files": { "pdf": "https://archive.orkl.eu/9d984e4a349304d5241f00ef7bea4afe618aac99.pdf", "text": "https://archive.orkl.eu/9d984e4a349304d5241f00ef7bea4afe618aac99.txt", "img": "https://archive.orkl.eu/9d984e4a349304d5241f00ef7bea4afe618aac99.jpg" } }