SID 1:59881

Rule Category

SERVER-OTHER -- Snort has detected traffic exploiting vulnerabilities in a server in the network.

Alert Message

SERVER-OTHER Citrix FileShare remote file inclusion attempt

Rule Explanation

This rule looks for a directory traversal in the http_uri at the vulnerable URL while attempting to validate that the service targeted could actually be exploited. This is a rule against the RCE, not the DOS.

What To Look For

This rule is triggered by a malicious HTTP message target Citrix FileShare for RCE.

Known Usage

Attacks/Scans seen in the wild

False Positives

No known false positives

Contributors

Cisco Talos Intelligence Group

Rule Groups

MITRE::ATT&CK Framework::Enterprise::Initial Access::Exploit Public-Facing Application

Adversaries may attempt to take advantage of a weakness in an Internet-facing computer or program using software, data, or commands in order to cause unintended or unanticipated behavior. The weakness in the system can be a bug, a glitch, or a design vulnerability. These applications are often websites, but can include databases (like SQL), standard services (like SMB or SSH), network device administration and management protocols (like SNMP and Smart Install), and any other applications with Internet accessible open sockets, such as web servers and related services.

MITRE::ATT&CK Framework::Enterprise::Initial Access::External Remote Services

Adversaries may leverage external-facing remote services to initially access and/or persist within a network. Remote services such as VPNs, Citrix, and other access mechanisms allow users to connect to internal enterprise network resources from external locations. There are often remote service gateways that manage connections and credential authentication for these services.

CVE

CVE-2021-22941

Additional Links

support.citrix.com/article/CTX328123

Rule Vulnerability

Remote File Inclusion

Remote File Inclusion (RFI) attacks occur when a webserver takes a file crafted by an attacker as input and runs or stores it in an unsafe manner. For instance, the webserver could accept an image file that is actually code, then call it to execute after uploading. RFI attacks happen on web applications that dynamically include external files or scripts. A successful RFI can lead to data leaks, remote code execution, or cross site scripting. Avoid dynamic inclusion of user input files, or whitelist files that may be included. Keep the PHP allow_url_include option set to off; this will not protect against Local File Inclusion attacks.

CVE Additional Information

This product uses data from the NVD API but is not endorsed or certified by the NVD.

CVE-2021-22941

Loading description

MITRE ATT&CK Framework

Tactic: Initial Access

Technique: Exploit Public-Facing Application

For reference, see the MITRE ATT&CK vulnerability types here: https://attack.mitre.org