Summary

The WMS specification defines an sld=<url> parameter for GetMap, GetLegendGraphic and GetFeatureInfo operations for user supplied "dynamic styling". Enabling the use of dynamic styles, without also configuring URL checks, provides the opportunity for Service Side Request Forgery. It is possible to use this for "Blind SSRF" on the WMS endpoint to steal NetNTLMv2 hashes via file requests to malicious servers.

Details

This vulnerability requires:

WMS Settings dynamic styling being enabled Security URL checks to be disabled, or to be enabled and allowing file:\\ access

Impact

This vulnerability can be used to steal user NetNTLMv2 hashes which could be relayed or cracked externally to gain further access.

Mitigation

The ability to reference an external URL location is defined by the WMS standard GetMap, GetFeatureInfo and GetLegendGraphic operations. These operations are defined by an Industry and International standard and cannot be redefined by the GeoServer application in isolation.

To disable dynamic styling on GeoServer 2.10.3 and GeoServer 2.11.1:

1. Navigate to Services > WMS Settings page 2. Locate Dynamic styling heading 3. Select the Disable usage of SLD and SLDBODY parameters in GET requests and user styles in POST checkbox.

Resolution

To allow dynamic styling safely on GeoServer 2.22.5 and GeoServer 2.23.2:

1. Navigate to Security > URL Checks 2. Enable URL Checks are enabled setting 3. Check the user manual for examples of how to trust specific locations: ^https://styles\.server\.net/cartography/.$ 4. Enable dynamic styling on the Services > WMS Settings page, deselect the Disable usage of SLD and SLDBODY parameters in GET requests and user styles in POST checkbox.

Use of dynamic styling safely is on by default in GeoServer 2.24.0.

References

Disabling usage of dynamic styling in GetMap, GetFeatureInfo and GetLegendGraphic requests URL Checks

GeoServer is an open source software server written in Java that allows users to share and edit geospatial data. The GeoServer security mechanism can perform an unchecked JNDI lookup, which in turn can be used to perform class deserialization and result in arbitrary code execution. The same can happen while configuring data stores with data sources located in JNDI, or while setting up the disk quota mechanism. In order to perform any of the above changes, the attack needs to have obtained admin rights and use either the GeoServer GUI, or its REST API. The lookups are going to be restricted in GeoServer 2.21.0, 2.20.4, 1.19.6. Users unable to upgrade should restrict access to the geoserver/web and geoserver/rest via a firewall and ensure that the GeoWebCache is not remotely accessible.