CWE-79
AllowedImproper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Abstraction: Base · Status: Stable
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.
68138 vulnerabilities reference this CWE, most recent first.
GHSA-VGJP-CGP8-G7F8
Vulnerability from github – Published: 2024-12-11 00:31 – Updated: 2024-12-11 00:31Adobe Experience Manager versions 6.5.21 and earlier are affected by a DOM-based Cross-Site Scripting (XSS) vulnerability that could allow an attacker to execute arbitrary code in the context of the victim's browser. This issue occurs when data from a malicious source is processed by a web application and subsequently written to the web page without proper sanitization, allowing for the execution of unintended script code or the alteration of the intended user interface. User interaction is required as the victim must visit a malicious page or view a maliciously crafted link.
{
"affected": [],
"aliases": [
"CVE-2024-43738"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-12-10T22:15:10Z",
"severity": "MODERATE"
},
"details": "Adobe Experience Manager versions 6.5.21 and earlier are affected by a DOM-based Cross-Site Scripting (XSS) vulnerability that could allow an attacker to execute arbitrary code in the context of the victim\u0027s browser. This issue occurs when data from a malicious source is processed by a web application and subsequently written to the web page without proper sanitization, allowing for the execution of unintended script code or the alteration of the intended user interface. User interaction is required as the victim must visit a malicious page or view a maliciously crafted link.",
"id": "GHSA-vgjp-cgp8-g7f8",
"modified": "2024-12-11T00:31:25Z",
"published": "2024-12-11T00:31:25Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-43738"
},
{
"type": "WEB",
"url": "https://helpx.adobe.com/security/products/experience-manager/apsb24-69.html"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N",
"type": "CVSS_V3"
}
]
}
GHSA-VGJQ-3M42-W385
Vulnerability from github – Published: 2024-05-14 15:32 – Updated: 2024-05-14 15:32IBM UrbanCode Deploy (UCD) 7.0 through 7.0.5.20, 7.1 through 7.1.2.16, 7.2 through 7.2.3.9, 7.3 through 7.3.2.4, and 8.0 through 8.0.0.1 is vulnerable to cross-site scripting. This vulnerability allows users to embed arbitrary JavaScript code in the Web UI thus altering the intended functionality potentially leading to credentials disclosure within a trusted session. IBM X-Force ID: 285654.
{
"affected": [],
"aliases": [
"CVE-2024-28781"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-05-14T15:14:41Z",
"severity": "MODERATE"
},
"details": "IBM UrbanCode Deploy (UCD) 7.0 through 7.0.5.20, 7.1 through 7.1.2.16, 7.2 through 7.2.3.9, 7.3 through 7.3.2.4, and 8.0 through 8.0.0.1 is vulnerable to cross-site scripting. This vulnerability allows users to embed arbitrary JavaScript code in the Web UI thus altering the intended functionality potentially leading to credentials disclosure within a trusted session. IBM X-Force ID: 285654.",
"id": "GHSA-vgjq-3m42-w385",
"modified": "2024-05-14T15:32:54Z",
"published": "2024-05-14T15:32:53Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-28781"
},
{
"type": "WEB",
"url": "https://exchange.xforce.ibmcloud.com/vulnerabilities/285654"
},
{
"type": "WEB",
"url": "https://www.ibm.com/support/pages/node/7150747"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N",
"type": "CVSS_V3"
}
]
}
GHSA-VGJR-6G84-W5J4
Vulnerability from github – Published: 2022-05-01 23:28 – Updated: 2025-04-09 03:50Multiple cross-site scripting (XSS) vulnerabilities in math-comment-spam-protection.php in the Math Comment Spam Protection 2.1 and earlier plugin for WordPress allow remote attackers to inject arbitrary web script or HTML via the (1) mcsp_opt_msg_no_answer or (2) mcsp_opt_msg_wrong_answer parameter to wp-admin/options-general.php.
{
"affected": [],
"aliases": [
"CVE-2008-0204"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2008-01-10T00:46:00Z",
"severity": "MODERATE"
},
"details": "Multiple cross-site scripting (XSS) vulnerabilities in math-comment-spam-protection.php in the Math Comment Spam Protection 2.1 and earlier plugin for WordPress allow remote attackers to inject arbitrary web script or HTML via the (1) mcsp_opt_msg_no_answer or (2) mcsp_opt_msg_wrong_answer parameter to wp-admin/options-general.php.",
"id": "GHSA-vgjr-6g84-w5j4",
"modified": "2025-04-09T03:50:10Z",
"published": "2022-05-01T23:28:22Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2008-0204"
},
{
"type": "WEB",
"url": "http://lists.grok.org.uk/pipermail/full-disclosure/2008-January/059439.html"
},
{
"type": "WEB",
"url": "http://securityreason.com/securityalert/3539"
},
{
"type": "WEB",
"url": "http://websecurity.com.ua/1576"
},
{
"type": "WEB",
"url": "http://www.securityfocus.com/archive/1/485786/100/0/threaded"
}
],
"schema_version": "1.4.0",
"severity": []
}
GHSA-VGJV-QPVM-QJX7
Vulnerability from github – Published: 2024-02-20 21:30 – Updated: 2024-08-06 18:30Cross Site Scripting vulnerability in the sanitize function in Enhancesoft osTicket 1.18.0 allows a remote attacker to escalate privileges via a crafted support ticket.
{
"affected": [],
"aliases": [
"CVE-2023-46967"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2024-02-20T21:15:07Z",
"severity": "MODERATE"
},
"details": "Cross Site Scripting vulnerability in the sanitize function in Enhancesoft osTicket 1.18.0 allows a remote attacker to escalate privileges via a crafted support ticket.",
"id": "GHSA-vgjv-qpvm-qjx7",
"modified": "2024-08-06T18:30:48Z",
"published": "2024-02-20T21:30:25Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2023-46967"
},
{
"type": "WEB",
"url": "https://www.sonarsource.com/blog/pitfalls-of-desanitization-leaking-customer-data-from-osticket"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
"type": "CVSS_V3"
}
]
}
GHSA-VGM8-MVFH-RJ89
Vulnerability from github – Published: 2025-08-21 18:31 – Updated: 2025-12-22 21:30Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') vulnerability in markdown-it allows Cross-Site Scripting (XSS). This vulnerability is associated with program files lib/renderer.mjs.
This issue affects markdown-it: 14.1.0.
{
"affected": [],
"aliases": [
"CVE-2025-7969"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-08-21T17:15:32Z",
"severity": "MODERATE"
},
"details": "Improper Neutralization of Input During Web Page Generation (XSS or \u0027Cross-site Scripting\u0027) vulnerability in markdown-it allows Cross-Site Scripting (XSS). This vulnerability is associated with program files lib/renderer.mjs.\n\nThis issue affects markdown-it: 14.1.0.",
"id": "GHSA-vgm8-mvfh-rj89",
"modified": "2025-12-22T21:30:31Z",
"published": "2025-08-21T18:31:29Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-7969"
},
{
"type": "WEB",
"url": "https://github.com/markdown-it/markdown-it/issues/1122"
},
{
"type": "WEB",
"url": "https://fluidattacks.com/advisories/fito"
},
{
"type": "WEB",
"url": "https://github.com/markdown-it/markdown-it"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
"type": "CVSS_V3"
},
{
"score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
"type": "CVSS_V4"
}
]
}
GHSA-VGMF-PG9P-7HRX
Vulnerability from github – Published: 2025-04-15 12:30 – Updated: 2026-04-01 18:34Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') vulnerability in RSTheme RS Elements Elementor Addon allows Stored XSS. This issue affects RS Elements Elementor Addon: from n/a through 1.1.5.
{
"affected": [],
"aliases": [
"CVE-2025-26745"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-04-15T12:15:19Z",
"severity": "MODERATE"
},
"details": "Improper Neutralization of Input During Web Page Generation (\u0027Cross-site Scripting\u0027) vulnerability in RSTheme RS Elements Elementor Addon allows Stored XSS. This issue affects RS Elements Elementor Addon: from n/a through 1.1.5.",
"id": "GHSA-vgmf-pg9p-7hrx",
"modified": "2026-04-01T18:34:41Z",
"published": "2025-04-15T12:30:24Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-26745"
},
{
"type": "WEB",
"url": "https://patchstack.com/database/wordpress/plugin/rselements-lite/vulnerability/wordpress-rs-elements-elementor-addon-plugin-1-1-5-stored-cross-site-scripting-xss-vulnerability?_s_id=cve"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L",
"type": "CVSS_V3"
}
]
}
GHSA-VGMH-PFX7-6657
Vulnerability from github – Published: 2026-07-14 18:32 – Updated: 2026-07-14 18:32Improper neutralization of input during web page generation ('cross-site scripting') in Microsoft Office SharePoint allows an authorized attacker to perform spoofing over a network.
{
"affected": [],
"aliases": [
"CVE-2026-55020"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2026-07-14T18:18:12Z",
"severity": "MODERATE"
},
"details": "Improper neutralization of input during web page generation (\u0027cross-site scripting\u0027) in Microsoft Office SharePoint allows an authorized attacker to perform spoofing over a network.",
"id": "GHSA-vgmh-pfx7-6657",
"modified": "2026-07-14T18:32:32Z",
"published": "2026-07-14T18:32:32Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-55020"
},
{
"type": "WEB",
"url": "https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-55020"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:U/C:L/I:L/A:N",
"type": "CVSS_V3"
}
]
}
GHSA-VGP4-2FC4-QFF2
Vulnerability from github – Published: 2026-08-12 14:40 – Updated: 2026-08-12 14:40Impact
Authenticated Backend Users with the backend.manage_editor ("Manage editor settings") permission can provide custom styles through Settings → Editor Settings → Markup Styles that are compiled through the LESS CSS parser and rendered on every backend page. Previously, the compiled output was not sanitized, which could have allowed a stored XSS attack.
Although this is a valid security issue, it's important to note that its severity is relatively low. To exploit the vulnerability, an attacker would already need to have trusted access to the Winter CMS backend with a specific administrative permission. The Winter CMS maintainers recommend that the backend.manage_editor permission only be granted to trusted administrators and developers.
A related issue exists in the custom CSS field at Settings → Customize Backend → Styles (backend.manage_branding permission), which uses the same rendering mechanism and is addressed separately.
All users are advised to update to the latest version to ensure their systems remain secure.
Patches
This issue has been patched in v1.2.13. The renderCss() method now applies strip_tags() to compiled CSS output before returning it.
Workarounds
Apply https://github.com/wintercms/winter/commit/d28f0b9474af79cfaa80eeb9d691f7a7c4469720 manually if unable to upgrade to v1.2.13.
Resources
- CVE-2025-61674 (identical vulnerability in October CMS, patched in v3.7.13 and v4.0.12)
{
"affected": [
{
"package": {
"ecosystem": "Packagist",
"name": "winter/wn-backend-module"
},
"ranges": [
{
"events": [
{
"introduced": "1.2.10"
},
{
"fixed": "1.2.13"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-32258"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": true,
"github_reviewed_at": "2026-08-12T14:40:38Z",
"nvd_published_at": null,
"severity": "HIGH"
},
"details": "### Impact \n \nAuthenticated Backend Users with the `backend.manage_editor` (\"Manage editor settings\") permission can provide custom styles through **Settings \u2192 Editor Settings \u2192 Markup Styles** that are compiled through the LESS CSS parser and rendered on every backend page. Previously, the compiled output was not sanitized, which could have allowed a stored XSS attack.\n\nAlthough this is a valid security issue, it\u0027s important to note that its severity is relatively low. To exploit the vulnerability, an attacker would already need to have trusted access to the Winter CMS backend with a specific administrative permission. The Winter CMS maintainers recommend that the `backend.manage_editor` permission only be granted to trusted administrators and developers.\n\nA related issue exists in the custom CSS field at **Settings \u2192 Customize Backend \u2192 Styles** (`backend.manage_branding` permission), which uses the same rendering mechanism and is addressed separately.\n\nAll users are advised to update to the latest version to ensure their systems remain secure.\n\n### Patches\n\nThis issue has been patched in v1.2.13. The `renderCss()` method now applies `strip_tags()` to compiled CSS output before returning it.\n\n### Workarounds\n\nApply [https://github.com/wintercms/winter/commit/d28f0b9474af79cfaa80eeb9d691f7a7c4469720](https://github.com/wintercms/winter/commit/d28f0b9474af79cfaa80eeb9d691f7a7c4469720) manually if unable to upgrade to v1.2.13.\n\n### Resources\n\n- CVE-2025-61674 (identical vulnerability in October CMS, patched in v3.7.13 and v4.0.12)",
"id": "GHSA-vgp4-2fc4-qff2",
"modified": "2026-08-12T14:40:38Z",
"published": "2026-08-12T14:40:38Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/wintercms/winter/security/advisories/GHSA-vgp4-2fc4-qff2"
},
{
"type": "WEB",
"url": "https://github.com/wintercms/winter/commit/d28f0b9474af79cfaa80eeb9d691f7a7c4469720"
},
{
"type": "PACKAGE",
"url": "https://github.com/wintercms/winter"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:H/I:H/A:N",
"type": "CVSS_V3"
}
],
"summary": "Winter: Stored XSS through Editor Settings custom styles"
}
GHSA-VGP5-9G3F-VWJ2
Vulnerability from github – Published: 2022-05-17 01:29 – Updated: 2025-04-11 04:17Cross-site scripting (XSS) vulnerability in KBKP Software HostBill before 2013-12-14 allows remote attackers to inject arbitrary web script or HTML via unspecified vectors.
{
"affected": [],
"aliases": [
"CVE-2013-7188"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2013-12-20T23:55:00Z",
"severity": "MODERATE"
},
"details": "Cross-site scripting (XSS) vulnerability in KBKP Software HostBill before 2013-12-14 allows remote attackers to inject arbitrary web script or HTML via unspecified vectors.",
"id": "GHSA-vgp5-9g3f-vwj2",
"modified": "2025-04-11T04:17:18Z",
"published": "2022-05-17T01:29:38Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2013-7188"
},
{
"type": "WEB",
"url": "https://blog.rack911.com/security-advisories/hostbill-xss-admin-hijack-security-vulnerability-r911-0099"
},
{
"type": "WEB",
"url": "https://exchange.xforce.ibmcloud.com/vulnerabilities/89750"
},
{
"type": "WEB",
"url": "http://extras.hostbillapp.com/security-advisory-hostbill-version-2013-12-14"
},
{
"type": "WEB",
"url": "http://hostbillapp.com/changelog"
},
{
"type": "WEB",
"url": "http://osvdb.org/101030"
},
{
"type": "WEB",
"url": "http://secunia.com/advisories/56124"
}
],
"schema_version": "1.4.0",
"severity": []
}
GHSA-VGP5-QC33-722H
Vulnerability from github – Published: 2022-11-25 21:30 – Updated: 2025-04-29 15:31Book Store Management System v1.0 was discovered to contain a cross-site scripting (XSS) vulnerability in /bsms_ci/index.php/book. This vulnerability allows attackers to execute arbitrary web scripts or HTML via a crafted payload injected into the book_title parameter.
{
"affected": [],
"aliases": [
"CVE-2022-45225"
],
"database_specific": {
"cwe_ids": [
"CWE-79"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2022-11-25T20:15:00Z",
"severity": "MODERATE"
},
"details": "Book Store Management System v1.0 was discovered to contain a cross-site scripting (XSS) vulnerability in /bsms_ci/index.php/book. This vulnerability allows attackers to execute arbitrary web scripts or HTML via a crafted payload injected into the book_title parameter.",
"id": "GHSA-vgp5-qc33-722h",
"modified": "2025-04-29T15:31:18Z",
"published": "2022-11-25T21:30:26Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2022-45225"
},
{
"type": "WEB",
"url": "https://medium.com/%40just0rg/book-store-management-system-1-0-unrestricted-input-leads-to-xss-74506d42492e"
},
{
"type": "WEB",
"url": "https://medium.com/@just0rg/book-store-management-system-1-0-unrestricted-input-leads-to-xss-74506d42492e"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N",
"type": "CVSS_V3"
}
]
}
Mitigation MIT-4
Strategy: Libraries or Frameworks
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid [REF-1482].
- Examples of libraries and frameworks that make it easier to generate properly encoded output include Microsoft's Anti-XSS library, the OWASP ESAPI Encoding module, and Apache Wicket.
Mitigation
- Understand the context in which your data will be used and the encoding that will be expected. This is especially important when transmitting data between different components, or when generating outputs that can contain multiple encodings at the same time, such as web pages or multi-part mail messages. Study all expected communication protocols and data representations to determine the required encoding strategies.
- For any data that will be output to another web page, especially any data that was received from external inputs, use the appropriate encoding on all non-alphanumeric characters.
- Parts of the same output document may require different encodings, which will vary depending on whether the output is in the:
- etc. Note that HTML Entity Encoding is only appropriate for the HTML body.
- Consult the XSS Prevention Cheat Sheet [REF-724] for more details on the types of encoding and escaping that are needed.
- HTML body
- Element attributes (such as src="XYZ")
- URIs
- JavaScript sections
- Cascading Style Sheets and style property
Mitigation MIT-6
Strategy: Attack Surface Reduction
Understand all the potential areas where untrusted inputs can enter your software: parameters or arguments, cookies, anything read from the network, environment variables, reverse DNS lookups, query results, request headers, URL components, e-mail, files, filenames, databases, and any external systems that provide data to the application. Remember that such inputs may be obtained indirectly through API calls.
Mitigation MIT-15
For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks entirely. Then, these modified values would be submitted to the server.
Mitigation MIT-27
Strategy: Parameterization
If available, use structured mechanisms that automatically enforce the separation between data and code. These mechanisms may be able to provide the relevant quoting, encoding, and validation automatically, instead of relying on the developer to provide this capability at every point where output is generated.
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.
Mitigation MIT-5
Strategy: Input Validation
- Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
- When performing input validation, consider all potentially relevant properties, including length, type of input, the full range of acceptable values, missing or extra inputs, syntax, consistency across related fields, and conformance to business rules. As an example of business rule logic, "boat" may be syntactically valid because it only contains alphanumeric characters, but it is not valid if the input is only expected to contain colors such as "red" or "blue."
- Do not rely exclusively on looking for malicious or malformed inputs. This is likely to miss at least one undesirable input, especially if the code's environment changes. This can give attackers enough room to bypass the intended validation. However, denylists can be useful for detecting potential attacks or determining which inputs are so malformed that they should be rejected outright.
- When dynamically constructing web pages, use stringent allowlists that limit the character set based on the expected value of the parameter in the request. All input should be validated and cleansed, not just parameters that the user is supposed to specify, but all data in the request, including 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. It is common to see 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.
- Note that proper output encoding, escaping, and quoting is the most effective solution for preventing XSS, although input validation may provide some defense-in-depth. This is because it effectively limits what will appear in output. Input validation will not always prevent XSS, especially if you are required to support free-form text fields that could contain arbitrary characters. For example, in a chat application, the heart emoticon ("<3") would likely pass the validation step, since it is commonly used. However, it cannot be directly inserted into the web page because it contains the "<" character, which would need to be escaped or otherwise handled. In this case, stripping the "<" might reduce the risk of XSS, but it would produce incorrect behavior because the emoticon would not be recorded. This might seem to be a minor inconvenience, but it would be more important in a mathematical forum that wants to represent inequalities.
- Even if you make a mistake in your validation (such as forgetting one out of 100 input fields), appropriate encoding is still likely to protect you from injection-based attacks. As long as it is not done in isolation, input validation is still a useful technique, since it may significantly reduce your attack surface, allow you to detect some attacks, and provide other security benefits that proper encoding does not address.
- Ensure that you perform input validation at well-defined interfaces within the application. This will help protect the application even if a component is reused or moved elsewhere.
Mitigation MIT-21
Strategy: Enforcement by Conversion
When the set of acceptable objects, such as filenames or URLs, is limited or known, create a mapping from a set of fixed input values (such as numeric IDs) to the actual filenames or URLs, and reject all other inputs.
Mitigation MIT-29
Strategy: Firewall
Use an application firewall that can detect attacks against this weakness. It can be beneficial in cases in which the code cannot be fixed (because it is controlled by a third party), as an emergency prevention measure while more comprehensive software assurance measures are applied, or to provide defense in depth [REF-1481].
Mitigation MIT-16
Strategy: Environment Hardening
When using PHP, configure the application so that it does not use register_globals. During implementation, develop the application so that it does not rely on this feature, but be wary of implementing a register_globals emulation that is subject to weaknesses such as CWE-95, CWE-621, and similar issues.
CAPEC-209: XSS Using MIME Type Mismatch
An adversary creates a file with scripting content but where the specified MIME type of the file is such that scripting is not expected. The adversary tricks the victim into accessing a URL that responds with the script file. Some browsers will detect that the specified MIME type of the file does not match the actual type of its content and will automatically switch to using an interpreter for the real content type. If the browser does not invoke script filters before doing this, the adversary's script may run on the target unsanitized, possibly revealing the victim's cookies or executing arbitrary script in their browser.
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.
CAPEC-591: Reflected XSS
This type of attack is a form of Cross-Site Scripting (XSS) where a malicious script is "reflected" off a vulnerable web application and then executed by a victim's browser. The process starts with an adversary delivering a malicious script to a victim and convincing the victim to send the script to the vulnerable web application.
CAPEC-592: Stored XSS
An adversary utilizes a form of Cross-site Scripting (XSS) where a malicious script is persistently "stored" within the data storage of a vulnerable web application as valid input.
CAPEC-63: Cross-Site Scripting (XSS)
An adversary embeds malicious scripts in content that will be served to web browsers. The goal of the attack is for the target software, the client-side browser, to execute the script with the users' privilege level. An attack of this type exploits a programs' vulnerabilities that are brought on by allowing remote hosts to execute code and scripts. Web browsers, for example, have some simple security controls in place, but if a remote attacker is allowed to execute scripts (through injecting them in to user-generated content like bulletin boards) then these controls may be bypassed. Further, these attacks are very difficult for an end user to detect.
CAPEC-85: AJAX Footprinting
This attack utilizes the frequent client-server roundtrips in Ajax conversation to scan a system. While Ajax does not open up new vulnerabilities per se, it does optimize them from an attacker point of view. A common first step for an attacker is to footprint the target environment to understand what attacks will work. Since footprinting relies on enumeration, the conversational pattern of rapid, multiple requests and responses that are typical in Ajax applications enable an attacker to look for many vulnerabilities, well-known ports, network locations and so on. The knowledge gained through Ajax fingerprinting can be used to support other attacks, such as XSS.