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RSS status feed does not set content type, leading to a Stored XSS in Public Status Page RSS Feed via CDATA escaped Monitor Name IF USING AN UNSECURE CLIENT

Low
louislam published GHSA-9fg7-wgm7-57fh Feb 8, 2026

Package

uptime-kuma

Affected versions

>= 2.0.0 && <= 2.0.2

Patched versions

2.1.0

Description

Summary

The RSS feed for public status pages returns a default text/html content type instead of a safe RSS/XML content type. Monitor names are already CDATA-escaped, so the content itself is safe. However, serving the feed as text/html can cause browsers to interpret it incorrectly, potentially exposing users to cross-site scripting if the feed is embedded in a web context.

Description

Monitor names are stored safely and rendered within CDATA sections in RSS feed items. The feed is generated dynamically and returned using response.send(). Because no explicit content type is set, the response defaults to text/html.

While the content is already escaped, serving it as HTML can cause browsers to parse the feed incorrectly, possibly leading to script execution in certain contexts, such as embedded feed readers or if the feed is opened directly in a browser. Setting the correct RSS/XML content type ensures browsers interpret the feed safely and reduces risk.

Affected Code

// server/model/status_page.js
response.send(await StatusPage.renderRSS(statusPage, slug));
// No Content-Type override (defaults to text/html)

Impact

  • Incorrect content type can lead to unsafe rendering in some browsers or feed readers
  • Low likelihood of XSS due to CDATA escaping, but setting a proper type mitigates potential risk
  • Affects anyone consuming the RSS feed in a browser context

Severity is assessed as Low, since user content is already escaped and the risk requires a specific client behavior.

Recommended Fix

  • Explicitly set the content type to a safe RSS/XML type:
response.type('application/rss+xml');
  • Ensure all user-controlled content remains properly escaped in CDATA sections
  • Optionally, apply a Content Security Policy (CSP) to further mitigate browser risks

CWE

  • CWE-116 – Improper Encoding or Escaping of Output

References

  • OWASP XSS Prevention Cheat Sheet – CDATA in XML/RSS
  • RFC 822 / RSS Security Considerations

Credits

Reported by: Bugbunny.ai

Severity

Low

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 Passive
Vulnerable System Impact Metrics
Confidentiality None
Integrity None
Availability None
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:P/VC:N/VI:N/VA:N/SC:N/SI:N/SA:N

CVE ID

No known CVE

Weaknesses

Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')

The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. Learn more on MITRE.

Credits