CWE-83
AllowedImproper Neutralization of Script in Attributes in a Web Page
Abstraction: Variant · Status: Draft
The product does not neutralize or incorrectly neutralizes "javascript:" or other URIs from dangerous attributes within tags, such as onmouseover, onload, onerror, or style.
42 vulnerabilities reference this CWE, most recent first.
GHSA-RHJ6-R49H-5932
Vulnerability from github – Published: 2026-06-18 15:04 – Updated: 2026-06-18 15:04TL;DR
This vulnerability affects Kirby sites that use the writer field in any blueprint.
It was possible to include a scripting link as the target of a link (or email link). This link target would then be clickable by the user who entered it.
A successful attack commonly requires knowledge of the content structure by the attacker as well as social engineering of a user with access to the Panel. The attack cannot be automated.
In Kirby's default configuration, the vulnerability is limited to self-XSS and cannot directly affect other users or visitors of the site. Panel plugins that are directly using the <k-writer> component may also be affected by stored XSS if they don't sanitize the resulting HTML before saving it to the content.
This vulnerability is of high severity for affected sites.
Introduction
Cross-site scripting (XSS) is a type of vulnerability that allows attackers to execute any kind of JavaScript code inside the Panel session of the same or other users. In the Panel, a harmful script can, for example, trigger requests to Kirby's API with the permissions of the victim.
Self cross-site scripting (self-XSS) typically involves a user inadvertently executing malicious code within their own context, often through social engineering techniques. This can occur when a user is tricked into pasting and executing malicious JavaScript code into the browser's developer console, address bar or form fields.
In a stored XSS attack, the malicious payload is saved into the content data and has the potential to affect other users or site visitors.
Such vulnerabilities are critical if you might have potential attackers in your group of authenticated Panel users. They can escalate their privileges if they get access to the Panel session of an admin user. Depending on your site, other JavaScript-powered attacks are possible.
Affected components
The writer field allows users to input formatted text, including links to arbitrary URLs and email addresses. Its link and email marks are therefore a target for XSS attacks.
As the vulnerability is in the writer mark components, it also affects all uses of the <k-writer> component in Panel plugins.
Impact
In affected releases, the link and email marks did not prevent XSS payloads from being submitted to the writer field's content data:
- The
linkmark allowed users to enter JavaScript URLs using the "custom" URL type. These URLs would already be sanitized by the backend before storing the malicious link in the content file. However, the link may be clicked by the same user who entered it before the content is saved. - The
emailmark was also vulnerable to injected JavaScript URLs. However, it was not possible to perform the attack via the Panel user interface due to email validation. The attack needed to be performed via a side channel such as the browser console.
The vulnerability allows attackers to inject malicious links into content. If the authenticated user clicked such a link before saving the content, the malicious script code would then be executed in their browser.
Patches
The problem has been patched in Kirby 4.9.4 and Kirby 5.4.4. Please update to one of these or a later version to fix the vulnerability.
In all of the mentioned releases, we have added more robust validation against dangerous URL schemes that are entered in the affected writer marks.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 4.9.3"
},
"package": {
"ecosystem": "Packagist",
"name": "getkirby/cms"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "4.9.4"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 5.4.3"
},
"package": {
"ecosystem": "Packagist",
"name": "getkirby/cms"
},
"ranges": [
{
"events": [
{
"introduced": "5.0.0-alpha.1"
},
{
"fixed": "5.4.4"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-49276"
],
"database_specific": {
"cwe_ids": [
"CWE-83"
],
"github_reviewed": true,
"github_reviewed_at": "2026-06-18T15:04:41Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "### TL;DR\n\nThis vulnerability affects Kirby sites that use the writer field in any blueprint.\n\nIt was possible to include a scripting link as the target of a link (or email link). This link target would then be clickable by the user who entered it.\n\nA successful attack commonly requires knowledge of the content structure by the attacker as well as social engineering of a user with access to the Panel. The attack *cannot* be automated.\n\nIn Kirby\u0027s default configuration, the vulnerability is limited to self-XSS and *cannot* directly affect other users or visitors of the site. Panel plugins that are directly using the `\u003ck-writer\u003e` component may also be affected by stored XSS if they don\u0027t sanitize the resulting HTML before saving it to the content.\n\n**This vulnerability is of high severity for affected sites.**\n\n----\n\n### Introduction\n\nCross-site scripting (XSS) is a type of vulnerability that allows attackers to execute any kind of JavaScript code inside the Panel session of the same or other users. In the Panel, a harmful script can, for example, trigger requests to Kirby\u0027s API with the permissions of the victim.\n\n*Self* cross-site scripting (self-XSS) typically involves a user inadvertently executing malicious code within their own context, often through social engineering techniques. This can occur when a user is tricked into pasting and executing malicious JavaScript code into the browser\u0027s developer console, address bar or form fields.\n\nIn a *stored* XSS attack, the malicious payload is saved into the content data and has the potential to affect other users or site visitors.\n\nSuch vulnerabilities are critical if you might have potential attackers in your group of authenticated Panel users. They can escalate their privileges if they get access to the Panel session of an admin user. Depending on your site, other JavaScript-powered attacks are possible.\n\n### Affected components\n\nThe `writer` field allows users to input formatted text, including links to arbitrary URLs and email addresses. Its `link` and `email` marks are therefore a target for XSS attacks.\n\nAs the vulnerability is in the writer mark components, it also affects all uses of the `\u003ck-writer\u003e` component in Panel plugins.\n\n### Impact\n\nIn affected releases, the `link` and `email` marks did not prevent XSS payloads from being submitted to the writer field\u0027s content data:\n\n- The `link` mark allowed users to enter JavaScript URLs using the \"custom\" URL type. These URLs would already be sanitized by the backend before storing the malicious link in the content file. However, the link may be clicked by the same user who entered it before the content is saved.\n- The `email` mark was also vulnerable to injected JavaScript URLs. However, it was not possible to perform the attack via the Panel user interface due to email validation. The attack needed to be performed via a side channel such as the browser console.\n\nThe vulnerability allows attackers to inject malicious links into content. If the authenticated user clicked such a link before saving the content, the malicious script code would then be executed in their browser.\n\n### Patches\n\nThe problem has been patched in [Kirby 4.9.4](https://github.com/getkirby/kirby/releases/tag/4.9.4) and [Kirby 5.4.4](https://github.com/getkirby/kirby/releases/tag/5.4.4). Please update to one of these or a [later version](https://github.com/getkirby/kirby/releases) to fix the vulnerability.\n\nIn all of the mentioned releases, we have added more robust validation against dangerous URL schemes that are entered in the affected writer marks.",
"id": "GHSA-rhj6-r49h-5932",
"modified": "2026-06-18T15:04:41Z",
"published": "2026-06-18T15:04:41Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/getkirby/kirby/security/advisories/GHSA-rhj6-r49h-5932"
},
{
"type": "PACKAGE",
"url": "https://github.com/getkirby/kirby"
},
{
"type": "WEB",
"url": "https://github.com/getkirby/kirby/releases/tag/4.9.4"
},
{
"type": "WEB",
"url": "https://github.com/getkirby/kirby/releases/tag/5.4.4"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:A/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N",
"type": "CVSS_V4"
}
],
"summary": "Kirby: Self cross-site scripting (self-XSS) in the writer field"
}
GHSA-VF6R-87Q4-2VJF
Vulnerability from github – Published: 2024-08-05 19:49 – Updated: 2025-05-15 21:26Summary
The navigateTo function attempts to blockthe javascript: protocol, but does not correctly use API's provided by unjs/ufo. This library also contains parsing discrepancies.
Details
The function first tests to see if the specified URL has a protocol. This uses the unjs/ufo package for URL parsing. This function works effectively, and returns true for a javascript: protocol.
After this, the URL is parsed using the parseURL function. This function will refuse to parse poorly formatted URLs. Parsing javascript:alert(1) returns null/"" for all values.
Next, the protocol of the URL is then checked using the isScriptProtocol function. This function simply checks the input against a list of protocols, and does not perform any parsing.
The combination of refusing to parse poorly formatted URLs, and not performing additional parsing means that script checks fail as no protocol can be found. Even if a protocol was identified, whitespace is not stripped in the parseURL implementation, bypassing the isScriptProtocol checks.
Certain special protocols are identified at the top of parseURL. Inserting a newline or tab into this sequence will block the special protocol check, and bypass the latter checks.
PoC
POC - https://stackblitz.com/edit/nuxt-xss-navigateto?file=app.vue
Attempt payload X, then attempt payload Y.
Impact
XSS, access to cookies, make requests on user's behalf.
Recommendations
As always with these bugs, the URL constructor provided by the browser is always the safest method of parsing a URL.
Given the cross-platform requirements of nuxt/ufo a more appropriate solution is to make parsing consistent between functions, and to adapt parsing to be more consistent with the WHATWG URL specification.
Note
I've reported this vulnerability here as it is unclear if this is a bug in ufo or a misuse of the ufo library.
This ONLY has impact after SSR has occurred, the javascript: protocol within a location header does not trigger XSS.
{
"affected": [
{
"package": {
"ecosystem": "npm",
"name": "nuxt"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "3.12.4"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2024-34343"
],
"database_specific": {
"cwe_ids": [
"CWE-79",
"CWE-83"
],
"github_reviewed": true,
"github_reviewed_at": "2024-08-05T19:49:22Z",
"nvd_published_at": "2024-08-05T21:15:38Z",
"severity": "MODERATE"
},
"details": "### Summary\nThe `navigateTo` function attempts to blockthe `javascript:` protocol, but does not correctly use API\u0027s provided by `unjs/ufo`. This library also contains parsing discrepancies.\n\n### Details\nThe function first tests to see if the specified [URL has a protocol](https://github.com/nuxt/nuxt/blob/fa9d43753d25fc2e8c3107f194b2bab6d4ebcb9a/packages/nuxt/src/app/composables/router.ts#L142). This uses the [unjs/ufo](https://github.com/unjs/ufo) package for URL parsing. This function works effectively, and returns true for a `javascript:` protocol.\n\nAfter this, the URL is parsed using the [`parseURL`](https://github.com/unjs/ufo/blob/e970686b2acae972136f478732450f6a2f1ab5e5/src/parse.ts#L47) function. This function will refuse to parse poorly formatted URLs. Parsing `javascript:alert(1)` returns null/\"\" for all values. \n\nNext, the protocol of the URL is then checked using the [`isScriptProtocol`](https://github.com/unjs/ufo/blob/e970686b2acae972136f478732450f6a2f1ab5e5/src/utils.ts#L74) function. This function simply checks the input against a list of protocols, and does not perform any parsing. \n\nThe combination of refusing to parse poorly formatted URLs, and not performing additional parsing means that script checks fail as no protocol can be found. Even if a protocol was identified, whitespace is not stripped in the `parseURL` implementation, bypassing the `isScriptProtocol` checks. \n\nCertain special protocols are identified at the top of [`parseURL`](https://github.com/unjs/ufo/blob/e970686b2acae972136f478732450f6a2f1ab5e5/src/parse.ts#L49). Inserting a newline or tab into this sequence will block the special protocol check, and bypass the latter checks. \n\n### PoC\nPOC - https://stackblitz.com/edit/nuxt-xss-navigateto?file=app.vue\n\nAttempt payload X, then attempt payload Y.\n\n### Impact\nXSS, access to cookies, make requests on user\u0027s behalf. \n\n### Recommendations\nAs always with these bugs, the `URL` constructor provided by the browser is always the safest method of parsing a URL. \n\nGiven the cross-platform requirements of nuxt/ufo a more appropriate solution is to make parsing consistent between functions, and to adapt parsing to be more consistent with the [WHATWG URL specification](https://url.spec.whatwg.org/).\n\n### Note\nI\u0027ve reported this vulnerability here as it is unclear if this is a bug in ufo or a misuse of the ufo library.\n\nThis ONLY has impact after SSR has occurred, the `javascript:` protocol within a location header does not trigger XSS.",
"id": "GHSA-vf6r-87q4-2vjf",
"modified": "2025-05-15T21:26:45Z",
"published": "2024-08-05T19:49:22Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/nuxt/nuxt/security/advisories/GHSA-vf6r-87q4-2vjf"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-34343"
},
{
"type": "PACKAGE",
"url": "https://github.com/nuxt/nuxt"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N",
"type": "CVSS_V4"
}
],
"summary": "nuxt vulnerable to Cross-site Scripting in navigateTo if used after SSR"
}
Mitigation
Carefully check each input parameter against a rigorous positive specification (allowlist) defining the specific characters and format allowed. All input should be neutralized, not just parameters that the user is supposed to specify, but all data in the request, including tag attributes, hidden fields, cookies, headers, the URL itself, and so forth. A common mistake that leads to continuing XSS vulnerabilities is to validate only fields that are expected to be redisplayed by the site. We often encounter data from the request that is reflected by the application server or the application that the development team did not anticipate. Also, a field that is not currently reflected may be used by a future developer. Therefore, validating ALL parts of the HTTP request is recommended.
Mitigation MIT-30.1
Strategy: Output Encoding
- Use and specify an output encoding that can be handled by the downstream component that is reading the output. Common encodings include ISO-8859-1, UTF-7, and UTF-8. When an encoding is not specified, a downstream component may choose a different encoding, either by assuming a default encoding or automatically inferring which encoding is being used, which can be erroneous. When the encodings are inconsistent, the downstream component might treat some character or byte sequences as special, even if they are not special in the original encoding. Attackers might then be able to exploit this discrepancy and conduct injection attacks; they even might be able to bypass protection mechanisms that assume the original encoding is also being used by the downstream component.
- The problem of inconsistent output encodings often arises in web pages. If an encoding is not specified in an HTTP header, web browsers often guess about which encoding is being used. This can open up the browser to subtle XSS attacks.
Mitigation MIT-43
With Struts, write all data from form beans with the bean's filter attribute set to true.
Mitigation MIT-31
Strategy: Attack Surface Reduction
To help mitigate XSS attacks against the user's session cookie, set the session cookie to be HttpOnly. In browsers that support the HttpOnly feature (such as more recent versions of Internet Explorer and Firefox), this attribute can prevent the user's session cookie from being accessible to malicious client-side scripts that use document.cookie. This is not a complete solution, since HttpOnly is not supported by all browsers. More importantly, XmlHttpRequest and other powerful browser technologies provide read access to HTTP headers, including the Set-Cookie header in which the HttpOnly flag is set.
CAPEC-243: XSS Targeting HTML Attributes
An adversary inserts commands to perform cross-site scripting (XSS) actions in HTML attributes. Many filters do not adequately sanitize attributes against the presence of potentially dangerous commands even if they adequately sanitize tags. For example, dangerous expressions could be inserted into a style attribute in an anchor tag, resulting in the execution of malicious code when the resulting page is rendered. If a victim is tricked into viewing the rendered page the attack proceeds like a normal XSS attack, possibly resulting in the loss of sensitive cookies or other malicious activities.
CAPEC-244: XSS Targeting URI Placeholders
An attack of this type exploits the ability of most browsers to interpret "data", "javascript" or other URI schemes as client-side executable content placeholders. This attack consists of passing a malicious URI in an anchor tag HREF attribute or any other similar attributes in other HTML tags. Such malicious URI contains, for example, a base64 encoded HTML content with an embedded cross-site scripting payload. The attack is executed when the browser interprets the malicious content i.e., for example, when the victim clicks on the malicious link.
CAPEC-588: DOM-Based XSS
This type of attack is a form of Cross-Site Scripting (XSS) where a malicious script is inserted into the client-side HTML being parsed by a web browser. Content served by a vulnerable web application includes script code used to manipulate the Document Object Model (DOM). This script code either does not properly validate input, or does not perform proper output encoding, thus creating an opportunity for an adversary to inject a malicious script launch a XSS attack. A key distinction between other XSS attacks and DOM-based attacks is that in other XSS attacks, the malicious script runs when the vulnerable web page is initially loaded, while a DOM-based attack executes sometime after the page loads. Another distinction of DOM-based attacks is that in some cases, the malicious script is never sent to the vulnerable web server at all. An attack like this is guaranteed to bypass any server-side filtering attempts to protect users.