CISA published a Malware Analysis Report (MAR) with analysis and associated detection signatures on files related to Microsoft SharePoint vulnerabilities:
Cyber threat actors have chained CVE-2025-49704 and CVE-2025-49706 (in an exploit chain publicly known as “ToolShell”) to gain unauthorized access to on-premises SharePoint servers. CISA analyzed six files including two Dynamic Link-Library (.DLL), one cryptographic key stealer, and three web shells. Cyber threat actors could leverage this malware to steal cryptographic keys and execute a Base64-encoded PowerShell command to fingerprint host system and exfiltrate data.
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Summary
Description
CISA received six files related to Microsoft SharePoint vulnerabilities: CVE-2025-49704 [CWE-94: Code Injection], CVE-2025-49706 [CWE-287: Improper Authentication], CVE-2025-53770 [CWE-502: Deserialization of Trusted Data], and CVE-2025-53771 [CWE-287: Improper Authentication]. According to Microsoft, cyber threat actors have chained CVE-2025-49706 (a network spoofing vulnerability) and CVE-2025-49704 (a remote code execution (RCE) vulnerability) in an exploit chain known as “ToolShell” to gain unauthorized access to on-premise SharePoint servers. Microsoft has not confirmed exploitation of CVE-2025-53771; however, CISA assesses exploitation is likely because it can be chained with CVE-2025-53770 to bypass previously disclosed vulnerabilities CVE-2025-49704 and CVE-2025-49706.
The analysis includes two Base64 encoded .NET Dynamic-link Library (DLL) binaries and four Active Server Page Extended [ASPX] files. The decoded DLLs are designed to retrieve machine key settings within an ASP[.]NET application’s configuration and add the retrieved machine key values to the Hypertext Transfer Protocol (HTTP) response header.
The first ASPX file is used to retrieve and output machine key information from an ASP[.]NET application’s configuration. The next ASPX file contains a command-line instruction used to execute a PowerShell command. The PowerShell command is designed to Base64 decode and install a malicious ASPX webshell on disk. The webshell is used to handle various web-related operations, including setting and retrieving HTTP cookies, command execution and uploading files. The remaining two ASPX webshells are used to execute a command using PowerShell on the server.
############ README ############### ## Edit rules and queries as needed for your hunt and based on your environment. ## Ensure your EDR/SIEM instance has enough memory to run these AND/OR condition based queries. May take longer to run than conventional Sigma rule query. ## Do not edit “logsource-product:” unless you are editing this rule to meet specific logsources/fields and know your environment. ## TLP GREEN + Please use local installation of Sigma to convert this rule. ## TLP CLEAR may convert rules using online converter of choice. ###################################
title: Detects ToolShell CVE-2025-53770 Exploitation IOCs and Activity incident: 251133.r1 tlp: CLEAR id: aba8967f-6613-47a8-87d1-e5d7aae31e9b status: test description: Detects ToolShell CVE-2025-53770 Exploitation of SharePoint servers. Previous related CVEs are CVE-2025-49706 and CVE-2025-49704. CVE-2025-53770 is new and stealthy webshell called SharpyShell, that extracts and leaks cryptographic secrets from the SharePoint server using a simple GET request. references: – https://www.cisa.gov/news-events/alerts/2025/07/20/microsoft-releases-guidance-exploitation-sharepoint-vulnerability-cve-2025-53770 – https://research.eye.security/sharepoint-under-siege/ – https://x.com/codewhitesec/status/1944743478350557232/photo/1 – 251132.r1 author: CISA Code & Media Analysis date: 2025-07-21 modified: 2025-07-22 tags: – cve.2025.53770 logsource: product: cma detection: keywords: – ’92bb4ddb98eeaf11fc15bb32e71d0a63256a0ed826a03ba293ce3a8bf057a514′ – ‘107.191.58.76’ – ‘104.238.159.149’ – ‘96.9.125.147’ – ‘Mozilla/5.0+(Windows+NT+10.0;+Win64;+x64;+rv:120.0)+Gecko/20100101+Firefox/120.0 /_layouts/SignOut.aspx’ – ‘-EncodedCommand JABiAGEAcwBlADYANABTAHQAcgBpAG4AZwAgAD0’ – ‘TEMPLATELAYOUTSspinstall0.aspx’ – ‘/_layouts/15/ToolPane.aspx DisplayMode=Edit’ – ‘/_layouts/15/spinstall0.aspx’ – ‘spinstall’ – ‘yoserial’
condition: keywords or keywords_1 and keywords_2 and keywords_3 or keywords_4 and keywords_5 and keywords_6 or keywords_7 and keywords_8 or keywords_9 and keywords_10 and keywords_11 and keywords_12 and keywords_13 and keywords_14 and keywords_15 and keywords_16 or keywords_17 and keywords_18 and keywords_19 and keywords_20 and keywords_21 or keywords_22 and keywords_23 and keywords_24 and keywords_25 or keywords_26 and keywords_27 and keywords_28
falsepositives: – Rate of FP moderate with some strings. – Use this rule in an infected environment/logs. – Analyst may need to make adjustments to the query as required. level: critical
############ README ############### ## Edit rules and queries as needed for your hunt and based on your environment. ## Ensure your EDR/SIEM instance has enough memory to run these AND/OR condition based queries. May take longer to run than conventional Sigma rule query. ## Do not edit “logsource-product:” unless you are editing this rule to meet specific logsources/fields and know your environment. ## TLP GREEN + Please use local installation of Sigma to convert this rule. ## TLP CLEAR may convert rules using online converter of choice. ###################################
condition: keywords_1 and keywords_2 and keywords_3 and keywords_4 and keywords_5 and keywords_6 or keywords_7 and keywords_8 and keywords_9 and keywords_10 and keywords_11 or keywords_12 and keywords_13 and keywords_14 or keywords_15 and keywords_16 or keywords_17 and keywords_18 and keywords_19
falsepositives: – Rate of FP low-moderate with some strings. – Use this rule in an infected environment/logs. – Analyst may need to make adjustments to the query as required. level: critical
This artifact is a 64-bit .NET DLL that contains a class named “E” (Figure 2) used to extract and concatenate machine key configuration settings within an ASP[.]NET application’s configuration. The file uses reflection to access the “MachineKeySection” from the “System.Web” assembly, which contains cryptographic keys used for validation and decryption in ASP[.]NET. The file uses reflection to get and invoke the “GetApplicationConfig” method of the “MachineKeySection” class to retrieve the “machineKey” configuration, which holds the actual key values. The file constructs a string containing the “ValidationKey”, “Validation”, “DecryptionKey”, “Decryption”, and “CompatibilityMode” properties of the “machineKeySection” and adds it as a custom header named “X-TXT-NET” to the HTTP response.
Screenshots
Figure 2 – Screenshot of the decompiled .NET assembly within a class named “E” used to extract the machine key configuration.
############ README ############### ## Edit rules and queries as needed for your hunt and based on your environment. ## Ensure your EDR/SIEM instance has enough memory to run these AND/OR condition based queries. May take longer to run than conventional Sigma rule query. ## Do not edit “logsource-product:” unless you are editing this rule to meet specific logsources/fields and know your environment. ## TLP GREEN + Please use local installation of Sigma to convert this rule. ## TLP CLEAR may convert rules using online converter of choice. ###################################
condition: keywords or keywords_1 and keywords_2 and keywords_3 or keywords_4 and keywords_5 and keywords_6 or keywords_7 and keywords_8 and keywords_9 or keywords_10 and keywords_11 and keywords_12 and keywords_13 and keywords_14 or keywords_15 and keywords_16 and keywords_17 and keywords_18 and keywords_19 and keywords_20 and keywords_21 or keywords_22 and keywords_23
falsepositives: – Rate of FP low-moderate with some strings. – Use this rule in an infected environment/logs. – Analyst may need to make adjustments to the query as required. level: critical
ssdeep Matches
No matches found.
PE Metadata
Compile Date
2025-07-22 08:33:22+00:00
Import Hash
dae02f32a21e03ce65412f6e56942daa
File Description
Internal Name
osvmhdfl.dll
Legal Copyright
Original Filename
osvmhdfl.dll
Product Version
0.0.0.0
PE Sections
MD5
Name
Raw Size
Entropy
2a11da5809d47c180a7aa559605259b5
header
512
2.545281
531ff1038e010be3c55de9cf1f212b56
.text
4608
4.532967
ef6793ef1a2f938cddc65b439e44ea07
.rsrc
1024
2.170401
403090c0870bb56c921d82a159dca5a3
.reloc
512
0.057257
Packers/Compilers/Cryptors
Microsoft Visual C# / Basic .NET
Description
This artifact is a 32-bit .NET DLL that contains a class named “E” (Figure 3) used to retrieve system and environment information, along with the machine key configuration settings (Figure 3). This class file is designed to iterate through and collect environment variables as well as retrieve and format .NET and system properties below:
–Begin System Properties– Number of logical drives Drive letters Computer name Full path of the system directory Current directory Processor count System uptime (milliseconds since start) Username Operating system version .NET version –End System Properties–
The file uses reflection to access the “MachineKeySection” from the “System.Web” assembly, which contains cryptographic keys used for validation and decryption in ASP[.]NET. The file uses reflection to invoke the “GetApplicationConfig” method of the “MachineKeySection” class to retrieve the “machineKey” configuration, which holds the actual key values. The file constructs a string containing the “ValidationKey”, “Validation”, “DecryptionKey”, “Decryption”, and “CompatibilityMode” properties of the “machineKeySection”. The gathered information and the “MachineKeySection” details are formatted into a string before written to the HTTP response (current.Response object).
Screenshots
Figure 3 – Screenshot of the decompiled .NET assembly that contains a class named “E” used to retrieve and display system and environment information, along with the machine key configuration settings.
rule CISA_251132_03 : steals_authentication_credentials exfiltrates_data { meta: author = “CISA Code & Media Analysis” incident = “251132” date = “2025-07-21” last_modified = “20250724_721” actor = “n/a” family = “n/a” capabilities = “steals-authentication-credentials exfiltrates-data” malware_type = “unknown” tool_type = “unknown” description = “Detects aspx payload samples” sha256_1 = “92bb4ddb98eeaf11fc15bb32e71d0a63256a0ed826a03ba293ce3a8bf057a514” strings: $s0 = { 4C 6F 61 64 28 22 53 79 73 74 65 6D 2E 57 65 62 } $s1 = { 43 6F 6E 66 69 67 75 72 61 74 69 6F 6E 2E 4D 61 63 68 69 6E 65 4B 65 79 53 65 63 74 69 6F 6E } $s2 = { 52 65 73 70 6F 6E 73 65 2E 57 72 69 74 65 } $s3 = { 63 67 2E 56 61 6C 69 64 61 74 69 6F 6E 4B 65 79 2B 22 7C 22 } $s4 = { 2B 63 67 2E 56 61 6C 69 64 61 74 69 6F 6E 2B } $s5 = { 2B 63 67 2E 44 65 63 72 79 70 74 69 6F 6E 4B 65 79 2B } $s6 = { 2B 63 67 2E 44 65 63 72 79 70 74 69 6F 6E 2B } $s7 = { 2B 63 67 2E 43 6F 6D 70 61 74 69 62 69 6C 69 74 79 4D 6F 64 65 } condition: all of them }
SIGMA Rule
No associated rule.
ssdeep Matches
No matches found.
Description
This artifact is a malicious ASPX file used to retrieve and output machine key information from the “MachineKeySection” of the System[.]Web[.]Configuration namespace (Figure 4). This file uses reflection to dynamically load the “System.Web” assembly and access the “MachineKeySection” class within “System.Web.Configuration”. The file invokes “GetApplicationConfig” to retrieve the “MachineKeySection” object and writes its properties including, ValidationKey, Validation, DecryptionKey, Decryption, and CompatibilityMode to the HTTP response using the “Response.Write()” method.
Screenshots
Figure 4 – Screenshot of the contents of the ASPX file used to extract configuration information from the machine key section of a web application’s Web.config file.
This artifact contains command-line instruction used to execute a PowerShell command (Figure 5). The PowerShell command decodes a Base64 encoded string into a Unicode Transformation Format-8 (UTF-8) string. The decoded content is then written to a file named “info3.aspx” (675a10e87c24….) located at c:progra~1\common~1micros~1webser~1l16templatelayouts. The output file is encoded using UTF8.
Screenshots
Figure 5 – Screenshot of the contents of the file containing command-line instruction used to execute a PowerShell command.
This artifact is a malicious ASP[.]NET web page (.aspx) that contains ASP[.]NET code embedded within an HTML structure. This file is a webshell installed by “info3.aspx” (9340bf73782….). The file handles various operations based on submitted form data or HTTP cookies. The file contains HTML code used to create forms. The forms allow the Threat Actor (TA) to enter a password and submit it using a “Login” button, enter a command into a text field, which can then be executed by clicking an “Execute” button, and upload files that includes two input fields: one for selecting a file (type=”file”) and another for text input (type=”text”) (Figure 7).
The password form element is configured for POST method and the input field is named “nYOmkVTYH2”. If the HTML form with a password is received from the TA via an HTTP POST request, the file checks if the submission form field parameter named “nYOmkVTYH2” is not null or empty. If the parameter is present and not empty, the file sets an HTTP Cookie named “wY1DC6wH4u” with a value from the form field “nYOmkVTYH2” and sets the HTTP Cookie expiration date to four days from the current time. This cookie is then added to the response. The file verifies if the HTTP cookie exists in the current HTTP request. If the cookie exists, its value is concatenated with a long hard-coded string “D&Fri2k&x5dMISTnaFq@ssyKk@rEM!98KzSKWpL4Nc8NvaA9AKdJVOtfdJ45FvbyYHxTql6kkc%qOZevc*hu^M#l#LrlNo9!7KLf”. This combined string is then hashed using SHA512. The computed hash is converted to a Base64 string and compared against a predefined Base64 encoded string “9gYs0W/reXzR+KO6J/zP6naMU9AQwZCwhmXuPyGeY2VwMkxNGBZaJQAxGS6GvQZJLSAPk8LT0PgJVU1kQQJd2zW9w==” (Figure 6). This process determines whether a user or request is authorized.
The command form element is configured for POST method and the input field is named “GTaRkhJ9wz”. If the HTML form with a command is received from the TA via an HTTP POST request, the file checks if the submission form field parameter named “GTaRkhJ9wz” is not null or empty. If the parameter is present and not empty, the file creates a new process to execute a command-line utility “cmd.exe”. The file redirects standard input, output, and error streams to capture the results of the executed command. The code writes the value of the “GTaRkhJ9wz” form parameter to the process’s standard input, executing the value as a command, and then writes “exit” to terminate the process (Figure 6).
The file upload form element is configured for POST method and “enctype”=”multipart/form-data” to handle file uploads. It includes an input type=”file” for selecting a file (input field named “0z3H8H8ato”) and an input type=”text” for providing a destination path or filename ( input field named “7KAjlfecWF”). If the HTML form for file upload is received from the TA, the file checks if the submission form field parameter named “7KAjlfecWF” (intended to be the file path or name) is not null or empty. The file retrieves the uploaded file through the “0z3H8H8atO” input using “HttpContext.Current[.]Request[.]Files[“Oz3H8H8ato”]”. If the file exists and has content (content length is greater than zero), the file saves the uploaded file using the path provided in the “7KAjlfecWF” field. Upon successful upload, the “InnerText” of an element named “Result” is set to “uploaded”, indicating the file has been saved. If an error occurs during the process, the file captures the exception and displays its details in “Result.InnerText” (Figure 6). The file displays server-side generated output or messages to the TA.
Screenshots
Figure 6 – Screenshot of the code snippet designed for handling various web-related operations, including setting and retrieving HTTP cookies, calculating a SHA512 hash of a request form value, starting an external cmd process and capturing its output, handling uploaded files from a request.
Figure 7 – Screenshot of the form that allows the TA to enter a password and submit it using a “Login” button, to enter a command, which can then be executed by clicking an “Execute” button, and a field for uploading files, featuring a file input (type=”file”) and a text input, both submitted using an “Upload” button.
This artifact is a malicious ASPX file with a “Page_Load” event handler that constructs and executes a command using PowerShell on the server (Figure 8). Upon execution, the file takes a Base64-encoded string from a form parameter named “p”. The Base64 encoded string is decoded and Exclusively-OR (XOR) decrypted using a hard-coded XOR key “68901a394a76dc5064fba96b862665ee596b1a1468bdc618157d7cca0130902e”. The output of the XOR decrypted bytes are converted to a Unicode Transformation Format-8 (UTF-8) string and then Base64 encoded. The Base64 encoded string is passed as an argument to the PowerShell process “powershell.exe” using the “-EncodedCommand flag”. The file redirects the standard output of the PowerShell process and reads it into a variable “o”, which is then written back to the HTTP response.
Screenshots
Figure 8 – Screenshot of the contents of the ASPX file.
This artifact is a malicious ASPX file with a “Page_Load” event handler that constructs and executes a command using PowerShell on the server (Figure 9). Upon execution, the file constructs a PowerShell command that decodes a Base64 string from the request form parameter “p”. The decoded string is decrypted using the XOR function with the hard-coded key “a859f0208777462899df67b3d81a7b8b”. The decrypted bytes (command) is executed using a PowerShell command. The standard output of the executed PowerShell command is converted to a UTF-8 string, then encrypted using the XOR function with the same hard-coded key. The encrypted bytes data is Base64 encoded before written to the HTTP response using “Response.Write”.
Screenshots
Figure 9 – Screenshot of the contents of the ASPX file.
CISA recommends that users and administrators consider using the following best practices to strengthen the security posture of their organization’s systems. Any configuration changes should be reviewed by system owners and administrators prior to implementation to avoid unwanted impacts.
Maintain up-to-date antivirus signatures and engines.
Keep operating system patches up-to-date.
Disable File and Printer sharing services. If these services are required, use strong passwords or Active Directory authentication.
Restrict users’ ability (permissions) to install and run unwanted software applications. Do not add users to the local administrators group unless required.
Enforce a strong password policy and implement regular password changes.
Exercise caution when opening e-mail attachments even if the attachment is expected and the sender appears to be known.
Enable a personal firewall on agency workstations, configured to deny unsolicited connection requests.
Disable unnecessary services on agency workstations and servers.
Scan for and remove suspicious e-mail attachments; ensure the scanned attachment is its “true file type” (i.e., the extension matches the file header).
Monitor users’ web browsing habits; restrict access to sites with unfavorable content.
Exercise caution when using removable media (e.g., USB thumb drives, external drives, CDs, etc.).
Scan all software downloaded from the Internet prior to executing.
Maintain situational awareness of the latest threats and implement appropriate Access Control Lists (ACLs).
Additional information on malware incident prevention and handling can be found in National Institute of Standards and Technology (NIST) Special Publication 800-83, “Guide to Malware Incident Prevention & Handling for Desktops and Laptops”.
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Document FAQ
What is a MIFR? A Malware Initial Findings Report (MIFR) is intended to provide organizations with malware analysis in a timely manner. In most instances this report will provide initial indicators for computer and network defense. To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.
What is a MAR? A Malware Analysis Report (MAR) is intended to provide organizations with more detailed malware analysis acquired via manual reverse engineering. To request additional analysis, please contact CISA and provide information regarding the level of desired analysis.
Can I edit this document? This document is not to be edited in any way by recipients. All comments or questions related to this document should be directed to the CISA at 1-888-282-0870 or CISA Service Desk.
Can I submit malware to CISA? Malware samples can be submitted via the methods below:
For larger files (over 100MB), please reach out to CISA for instructions.
CISA encourages you to report any suspicious activity, including cybersecurity incidents, possible malicious code, software vulnerabilities, and phishing-related scams. Reporting forms can be found on CISA’s homepage at www.cisa.gov.
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