VulnerabilityPublished 12 Mar 2026

CVE-2026-3990: CesiumGS CesiumJS · Cross-site Scripting

Affects CesiumGS CesiumJSSource CVE Database V5

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Mentioned vulnerabilities

CVE-2023-48094

Public exploit available · CVSS 5.3 Medium.

Data as of 30 Oct 2026, 11:52 UTC

CVSS 4.0 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.2% chance of exploitation in 30 days – higher than 20% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:P

Base metrics

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: None
Privileges Required: None
User Interaction: Passive
Vulnerable system confidentiality: None
Vulnerable system integrity: Low
Vulnerable system availability: None
Subsequent system confidentiality: None
Subsequent system integrity: None
Subsequent system availability: None

Threat metrics

Exploit Maturity: POC

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, up to and including the entire Internet. Such a vulnerability is often termed “remotely exploitable” and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: None: The successful attack does not depend on the deployment and execution conditions of the vulnerable system. The attacker can expect to be able to reach the vulnerability and execute the exploit under all or most instances of the vulnerability.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: Passive: Successful exploitation of this vulnerability requires limited interaction by the targeted user with the vulnerable system and the attacker’s payload. These interactions would be considered involuntary and do not require that the user actively subvert protections built into the vulnerable system.
Vulnerable system confidentiality: None: There is no loss of confidentiality within the Vulnerable System.
Vulnerable system integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact to the Vulnerable System.
Vulnerable system availability: None: There is no impact to availability within the Vulnerable System.
Subsequent system confidentiality: None: There is no loss of confidentiality within the Subsequent System or all confidentiality impact is constrained to the Vulnerable System.
Subsequent system integrity: None: There is no loss of integrity within the Subsequent System or all integrity impact is constrained to the Vulnerable System.
Subsequent system availability: None: There is no impact to availability within the Subsequent System or all availability impact is constrained to the Vulnerable System.
Exploit Maturity: POC: Based on threat intelligence sources each of the following must apply: · Proof-of-concept is publicly available · No knowledge of reported attempts to exploit this vulnerability · No knowledge of publicly available solutions used to simplify attempts to exploit the vulnerability

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 12 Mar 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
CVSS exploit maturity: proof of concept public
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), CVSS vector, the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Affected software

Product	Affected	Fixed in
CesiumGSCesiumJS	Affected =1.137	Fixed in–
GitHubcesiumgs/cesium`pkg:github/cesiumgs/cesium`Other threats	Affected =1.137	Fixed in–

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Immediately review all deployments of CesiumJS to determine if the Apps/Sandcastle/standalone.html demo file is exposed to end users or integrated into production environments.
If the demo application is not required, remove or restrict access to the Sandcastle directory and standalone.html file to prevent exposure.
Implement strict input validation and output encoding on any parameters, especially the 'c' argument, to neutralize potential script injection vectors.
Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers accessing the application.
Monitor web server logs for suspicious requests targeting the vulnerable parameter and unusual user activity indicative of exploitation attempts.
Consider isolating or sandboxing the demo application environment to limit the impact of any potential compromise.
Stay alert for any vendor updates or community patches addressing this vulnerability and apply them promptly.
Educate users about the risks of interacting with untrusted links or inputs within CesiumJS-based applications.
If feasible, contribute to or engage with the CesiumGS community to encourage official remediation or clarification regarding the vulnerability status.

Description

A security flaw has been discovered in CesiumGS CesiumJS up to 1.137.0. Affected by this issue is some unknown functionality of the file Apps/Sandcastle/standalone.html. The manipulation of the argument c results in cross site scripting. The attack can be launched remotely. The exploit has been released to the public and may be used for attacks. The presence of this vulnerability remains uncertain at this time. The vendor was contacted early about this disclosure but did not respond in any way. According to CVE-2023-48094, "the vendor's position is that Apps/Sandcastle/standalone.html is part of the CesiumGS/cesium GitHub repository, but is demo code that is not part of the CesiumJS JavaScript library product."

Impact

The primary impact of CVE-2026-3990 is the potential for attackers to execute arbitrary JavaScript in the context of users interacting with the vulnerable Sandcastle demo application. This can lead to theft of sensitive information such as session cookies, user credentials, or other confidential data accessible via the browser. Additionally, attackers could perform actions on behalf of the user, manipulate the user interface, or deliver further malicious payloads. Although the vulnerability is confined to demo code, organizations that expose this component publicly or integrate it into their environments risk compromising user trust and data integrity. The lack of vendor response and patch increases the window of exposure. The vulnerability does not affect system availability directly but can undermine confidentiality and integrity. Given CesiumJS's use in geospatial visualization, mapping, and defense-related applications, exploitation could have broader implications if attackers leverage this vector to gain footholds or pivot to other systems. The medium severity score reflects moderate risk, but the ease of remote exploitation and public exploit availability elevate the threat level for affected deployments.

Summary

CVE-2026-3990 is a cross-site scripting vulnerability identified in CesiumGS CesiumJS versions up to 1.137.0. The issue resides specifically in the Apps/Sandcastle/standalone.html file, which is part of the CesiumGS GitHub repository but considered demo code rather than part of the core CesiumJS library product. The vulnerability arises from improper handling of the 'c' argument, allowing an attacker to inject malicious scripts that execute in the context of a victim's browser. This flaw can be exploited remotely without requiring authentication, though it does require user interaction to trigger the malicious payload. The vendor has not responded to the disclosure and has not released a patch, citing the affected file as non-production demo code. The vulnerability has a CVSS 4.0 base score of 5.3, reflecting medium severity, with attack vector being network-based, low attack complexity, no privileges or user interaction required for initial access, but user interaction needed to trigger the XSS. The impact primarily affects confidentiality and integrity by enabling script injection, which can lead to session hijacking, credential theft, or execution of arbitrary code within the victim's browser session. While no known exploits in the wild have been reported, the public availability of exploit code increases the risk of opportunistic attacks. Organizations using CesiumJS should assess whether they expose the vulnerable demo application or incorporate the affected file in their deployments and take appropriate measures to mitigate risk.

References

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