Common Weakness Enumeration
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.
66712 vulnerabilities reference this CWE, most recent first.
CVE-2026-33979 (GCVE-0-2026-33979)
Vulnerability from cvelistv5 – Published: 2026-03-27 21:29 – Updated: 2026-03-31 14:29
VLAI
EPSS
VEX
Title
Express XSS Sanitizer: allowedTags/allowedAttributes bypass leads to permissive sanitization (XSS risk)
Summary
Express XSS Sanitizer is Express 4.x and 5.x middleware which sanitizes user input data (in req.body, req.query, req.headers and req.params) to prevent Cross Site Scripting (XSS) attack. A vulnerability has been identified in versions prior to 2.0.2 where restrictive sanitization configurations are silently ignored. In version 2.0.2, the validation logic has been updated to respect explicitly provided empty configurations. Now, if allowedTags or allowedAttributes are provided (even if empty), they are passed directly to sanitize-html without being overridden.
Severity
8.2 (High)
SSVC
Exploitation: poc
Automatable: yes
Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
Assigner
References
3 references
| URL | Tags |
|---|---|
| https://github.com/AhmedAdelFahim/express-xss-san… | x_refsource_CONFIRM |
| https://github.com/AhmedAdelFahim/express-xss-san… | x_refsource_MISC |
| https://github.com/AhmedAdelFahim/express-xss-san… | x_refsource_MISC |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| AhmedAdelFahim | express-xss-sanitizer |
Affected:
< 2.0.2
|
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CVE-2026-33978 (GCVE-0-2026-33978)
Vulnerability from cvelistv5 – Published: 2026-04-01 16:11 – Updated: 2026-04-01 19:07
VLAI
EPSS
VEX
Title
Notesnook: Stored XSS in mobile share editor via unescaped web clip title metadata
Summary
Notesnook is a note-taking app focused on user privacy & ease of use. Prior to version 3.3.17, a stored XSS vulnerability exists in the mobile share / web clip flow because attacker-controlled clip metadata is concatenated into HTML without escaping and then rendered with innerHTML inside the mobile share editor WebView. An attacker can control the shared title metadata (for example through Android/iOS share metadata such as TITLE / SUBJECT, or through link-preview title data) and inject HTML such as </a><img src=x onerror=...>. When the victim opens the Notesnook share flow and selects Web clip, the payload is inserted into the generated HTML and executed in the mobile editor WebView. This issue has been patched in version 3.3.17.
Severity
5.4 (Medium)
SSVC
Exploitation: poc
Automatable: no
Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
- CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Assigner
References
3 references
| URL | Tags |
|---|---|
| https://github.com/streetwriters/notesnook/securi… | x_refsource_CONFIRM |
| https://github.com/streetwriters/notesnook/commit… | x_refsource_MISC |
| https://github.com/streetwriters/notesnook/releas… | x_refsource_MISC |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| streetwriters | notesnook |
Affected:
< 3.3.17
|
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CVE-2026-33976 (GCVE-0-2026-33976)
Vulnerability from cvelistv5 – Published: 2026-03-27 21:26 – Updated: 2026-04-03 03:55
VLAI
EPSS
VEX
Title
Notesnook vulnerable to RCE via stored XSS in Web Clipper rendering
Summary
Notesnook is a note-taking app. Prior to version 3.3.11 on Web/Desktop and 3.3.17 on Android/iOS, a stored XSS in the Web Clipper rendering flow can be escalated to remote code execution in the desktop app. The root cause is that the clipper preserves attacker-controlled attributes from the source page’s root element and stores them inside web-clip HTML. When the clip is later opened, Notesnook renders that HTML into a same-origin, unsandboxed iframe using `contentDocument.write(...)`. Event-handler attributes such as `onload`, `onclick`, or `onmouseover` execute in the Notesnook origin. In the desktop app, this becomes RCE because Electron is configured with `nodeIntegration: true` and `contextIsolation: false`. Version 3.3.11 Web/Desktop and 3.3.17 on Android/iOS patch the issue.
Severity
9.7 (Critical)
SSVC
Exploitation: poc
Automatable: no
Technical Impact: total
CISA Coordinator (v2.0.3)
CWE
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://github.com/streetwriters/notesnook/securi… | x_refsource_CONFIRM |
Impacted products
2 products
| Vendor | Product | Version | |
|---|---|---|---|
| streetwriters | Notesnook Web/Desktop |
Affected:
< 3.3.11
|
|
| streetwriters | Notesnook iOS/Android |
Affected:
< 3.3.17
|
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CVE-2026-33955 (GCVE-0-2026-33955)
Vulnerability from cvelistv5 – Published: 2026-03-27 21:27 – Updated: 2026-04-03 13:02
VLAI
EPSS
VEX
Title
Notesnook vulnerable to RCE via stored XSS in Note History diff viewer
Summary
Notesnook is a note-taking app. Prior to version 3.3.11 on Web/Desktop, a cross-site scripting vulnerability stored in the note history comparison viewer can escalate to remote code execution in a desktop application. The issue is triggered when an attacker-controlled note header is displayed using `dangerouslySetInnerHTML` without secure handling. When combined with the full backup and restore feature in the desktop application, this becomes remote code execution because Electron is configured with `nodeIntegration: true` and `contextIsolation: false`. Version 3.3.11 patches the issue.
Severity
8.6 (High)
SSVC
Exploitation: poc
Automatable: no
Technical Impact: total
CISA Coordinator (v2.0.3)
CWE
Assigner
References
1 reference
| URL | Tags |
|---|---|
| https://github.com/streetwriters/notesnook/securi… | x_refsource_CONFIRM |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| streetwriters | Notesnook Web/Desktop |
Affected:
< 3.3.11
|
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CVE-2026-33941 (GCVE-0-2026-33941)
Vulnerability from cvelistv5 – Published: 2026-03-27 21:13 – Updated: 2026-07-15 01:05
VLAI
EPSS
VEX
Title
Handlebars.js has JavaScript Injection in CLI Precompiler via Unescaped Names and Options
Summary
Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, the Handlebars CLI precompiler (`bin/handlebars` / `lib/precompiler.js`) concatenates user-controlled strings — template file names and several CLI options — directly into the JavaScript it emits, without any escaping or sanitization. An attacker who can influence template filenames or CLI arguments can inject arbitrary JavaScript that executes when the generated bundle is loaded in Node.js or a browser. Version 4.7.9 fixes the issue. Some workarounds are available. First, validate all CLI inputs before invoking the precompiler. Reject filenames and option values that contain characters with JavaScript string-escaping significance (`"`, `'`, `;`, etc.). Second, use a fixed, trusted namespace string passed via a configuration file rather than command-line arguments in automated pipelines. Third, run the precompiler in a sandboxed environment (container with no write access to sensitive paths) to limit the impact of successful exploitation. Fourth, audit template filenames in any repository or package that is consumed by an automated build pipeline.
Severity
8.3 (High)
SSVC
Exploitation: poc
Automatable: no
Technical Impact: total
CISA Coordinator (v2.0.3)
CWE
Assigner
References
8 references
| URL | Tags |
|---|---|
| https://github.com/handlebars-lang/handlebars.js/… | x_refsource_CONFIRM |
| https://github.com/handlebars-lang/handlebars.js/… | x_refsource_MISC |
| https://github.com/handlebars-lang/handlebars.js/… | x_refsource_MISC |
| https://access.redhat.com/security/cve/CVE-2026-33941 | vdb-entryx_refsource_REDHAT |
| https://bugzilla.redhat.com/show_bug.cgi?id=2452524 | issue-trackingx_refsource_REDHAT |
| https://security.access.redhat.com/data/csaf/v2/v… | x_sadp-csaf-vex |
| https://access.redhat.com/errata/RHSA-2026:34342 | vendor-advisoryx_refsource_REDHAT |
| https://access.redhat.com/errata/RHSA-2026:10175 | vendor-advisoryx_refsource_REDHAT |
Impacted products
14 products
| Vendor | Product | Version | |
|---|---|---|---|
| handlebars-lang | handlebars.js |
Affected:
>= 4.0.0, < 4.7.9
|
|
| Red Hat | Cluster Observability Operator 1.5.0 |
Unaffected:
1782839279 , < *
(rpm)
cpe:/a:redhat:cluster_observability_operator:1.5::el9 |
|
| Red Hat | Cluster Observability Operator 1.5.0 |
Unaffected:
1782840539 , < *
(rpm)
cpe:/a:redhat:cluster_observability_operator:1.5::el9 |
|
| Red Hat | Cluster Observability Operator 1.5.0 |
Unaffected:
1782839996 , < *
(rpm)
cpe:/a:redhat:cluster_observability_operator:1.5::el9 |
|
| Red Hat | Red Hat OpenShift Dev Spaces 3.27 |
Unaffected:
1776744110 , < *
(rpm)
cpe:/a:redhat:openshift_devspaces:3.27::el9 |
|
| Red Hat | Cryostat 4 |
cpe:/a:redhat:cryostat:4 |
|
| Red Hat | Logging Subsystem for Red Hat OpenShift |
cpe:/a:redhat:logging:5 |
|
| Red Hat | Red Hat Data Grid 8 |
cpe:/a:redhat:jboss_data_grid:8 |
|
| Red Hat | Red Hat Enterprise Linux 10 |
cpe:/o:redhat:enterprise_linux:10 |
|
| Red Hat | Red Hat Enterprise Linux 7 |
cpe:/o:redhat:enterprise_linux:7 |
|
| Red Hat | Red Hat Enterprise Linux 8 |
cpe:/o:redhat:enterprise_linux:8 |
|
| Red Hat | Red Hat Enterprise Linux 9 |
cpe:/o:redhat:enterprise_linux:9 |
|
| Red Hat | Red Hat OpenShift AI (RHOAI) |
cpe:/a:redhat:openshift_ai |
|
| Red Hat | Red Hat Process Automation 7 |
cpe:/a:redhat:jboss_enterprise_bpms_platform:7 |
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CVE-2026-33933 (GCVE-0-2026-33933)
Vulnerability from cvelistv5 – Published: 2026-03-25 23:40 – Updated: 2026-03-26 14:23
VLAI
EPSS
VEX
Title
Reflected XSS via Unescaped contextName Parameter in Custom Template Editor
Summary
OpenEMR is a free and open source electronic health records and medical practice management application. Starting in version 7.0.2.1 and prior to version 8.0.0.3, a reflected cross-site scripting (XSS) vulnerability in the custom template editor allows an attacker to execute arbitrary JavaScript in an authenticated staff member's browser session by sending them a crafted URL. The attacker does not need an OpenEMR account. Version 8.0.0.3 patches the issue.
Severity
6.1 (Medium)
SSVC
Exploitation: poc
Automatable: no
Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
- CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://github.com/openemr/openemr/security/advis… | x_refsource_CONFIRM |
| https://github.com/openemr/openemr/commit/d5c8d49… | x_refsource_MISC |
| https://github.com/openemr/openemr/commit/de9b6eb… | x_refsource_MISC |
| https://github.com/openemr/openemr/releases/tag/v… | x_refsource_MISC |
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CVE-2026-33932 (GCVE-0-2026-33932)
Vulnerability from cvelistv5 – Published: 2026-03-25 23:37 – Updated: 2026-03-30 14:56
VLAI
EPSS
VEX
Title
OpenEMR has Stored XSS in CCDA Preview via Unsanitized linkHtml Attributes
Summary
OpenEMR is a free and open source electronic health records and medical practice management application. Prior to version 8.0.0.3, a stored cross-site scripting vulnerability in the CCDA document preview allows an attacker who can upload or send a CCDA document to execute arbitrary JavaScript in a clinician's browser session when the document is previewed. The XSL stylesheet sanitizes attributes for all other narrative elements but not for `linkHtml`, allowing `href="javascript:..."` and event handler attributes to pass through unchanged. Version 8.0.0.3 patches the issue.
Severity
7.6 (High)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
- CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Assigner
References
3 references
| URL | Tags |
|---|---|
| https://github.com/openemr/openemr/security/advis… | x_refsource_CONFIRM |
| https://github.com/openemr/openemr/commit/95e6078… | x_refsource_MISC |
| https://github.com/openemr/openemr/releases/tag/v… | x_refsource_MISC |
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CVE-2026-33916 (GCVE-0-2026-33916)
Vulnerability from cvelistv5 – Published: 2026-03-27 21:00 – Updated: 2026-03-30 15:41
VLAI
EPSS
VEX
Title
Handlebars.js has Prototype Pollution Leading to XSS through Partial Template Injection
Summary
Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, `resolvePartial()` in the Handlebars runtime resolves partial names via a plain property lookup on `options.partials` without guarding against prototype-chain traversal. When `Object.prototype` has been polluted with a string value whose key matches a partial reference in a template, the polluted string is used as the partial body and rendered without HTML escaping, resulting in reflected or stored XSS. Version 4.7.9 fixes the issue. Some workarounds are available. Apply `Object.freeze(Object.prototype)` early in application startup to prevent prototype pollution. Note: this may break other libraries, and/or use the Handlebars runtime-only build (`handlebars/runtime`), which does not compile templates and reduces the attack surface.
Severity
4.7 (Medium)
SSVC
Exploitation: poc
Automatable: no
Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
Assigner
References
3 references
| URL | Tags |
|---|---|
| https://github.com/handlebars-lang/handlebars.js/… | x_refsource_CONFIRM |
| https://github.com/handlebars-lang/handlebars.js/… | x_refsource_MISC |
| https://github.com/handlebars-lang/handlebars.js/… | x_refsource_MISC |
Impacted products
1 product
| Vendor | Product | Version | |
|---|---|---|---|
| handlebars-lang | handlebars.js |
Affected:
>= 4.0.0, < 4.7.9
|
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CVE-2026-33912 (GCVE-0-2026-33912)
Vulnerability from cvelistv5 – Published: 2026-03-25 22:51 – Updated: 2026-03-26 14:24
VLAI
EPSS
VEX
Title
OpenEMR has reflected XSS in ajax_download.php via reportID parameter
Summary
OpenEMR is a free and open source electronic health records and medical practice management application. Prior to version 8.0.0.3, an authenticated attacker could craft a malicious form that, when submitted by a victim, executes arbitrary JavaScript in the victim's browser session. Version 8.0.0.3 patches the issue.
Severity
5.4 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
- CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Assigner
References
4 references
| URL | Tags |
|---|---|
| https://github.com/openemr/openemr/security/advis… | x_refsource_CONFIRM |
| https://github.com/openemr/openemr/commit/24dd47c… | x_refsource_MISC |
| https://github.com/openemr/openemr/commit/ae2a9e5… | x_refsource_MISC |
| https://github.com/openemr/openemr/releases/tag/v… | x_refsource_MISC |
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CVE-2026-33911 (GCVE-0-2026-33911)
Vulnerability from cvelistv5 – Published: 2026-03-25 22:44 – Updated: 2026-03-26 15:02
VLAI
EPSS
VEX
Title
OpenEMR vulnerable to reflected XSS in graphs.php via title parameter
Summary
OpenEMR is a free and open source electronic health records and medical practice management application. Prior to version 8.0.0.3, the POST parameter `title` is reflected back in a JSON response built with `json_encode()`. Because the response is served with a `text/html` Content-Type, the browser interprets injected HTML/script tags rather than treating the output as JSON. An authenticated attacker can craft a request that executes arbitrary JavaScript in a victim's session. Version 8.0.0.3 contains a fix.
Severity
5.4 (Medium)
SSVC
Exploitation: none
Automatable: no
Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
- CWE-79 - Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting')
Assigner
References
3 references
| URL | Tags |
|---|---|
| https://github.com/openemr/openemr/security/advis… | x_refsource_CONFIRM |
| https://github.com/openemr/openemr/commit/64e8bef… | x_refsource_MISC |
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"scope": "CHANGED",
"userInteraction": "REQUIRED",
"vectorString": "CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N",
"version": "3.1"
}
}
],
"problemTypes": [
{
"descriptions": [
{
"cweId": "CWE-79",
"description": "CWE-79: Improper Neutralization of Input During Web Page Generation (\u0027Cross-site Scripting\u0027)",
"lang": "en",
"type": "CWE"
}
]
}
],
"providerMetadata": {
"dateUpdated": "2026-03-25T22:44:13.107Z",
"orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
"shortName": "GitHub_M"
},
"references": [
{
"name": "https://github.com/openemr/openemr/security/advisories/GHSA-wwhf-6cvc-6766",
"tags": [
"x_refsource_CONFIRM"
],
"url": "https://github.com/openemr/openemr/security/advisories/GHSA-wwhf-6cvc-6766"
},
{
"name": "https://github.com/openemr/openemr/commit/64e8befa0a49f85dd5e2a85c91f3f8b9e565896f",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/openemr/openemr/commit/64e8befa0a49f85dd5e2a85c91f3f8b9e565896f"
},
{
"name": "https://github.com/openemr/openemr/releases/tag/v8_0_0_3",
"tags": [
"x_refsource_MISC"
],
"url": "https://github.com/openemr/openemr/releases/tag/v8_0_0_3"
}
],
"source": {
"advisory": "GHSA-wwhf-6cvc-6766",
"discovery": "UNKNOWN"
},
"title": "OpenEMR vulnerable to reflected XSS in graphs.php via title parameter"
}
},
"cveMetadata": {
"assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
"assignerShortName": "GitHub_M",
"cveId": "CVE-2026-33911",
"datePublished": "2026-03-25T22:44:13.107Z",
"dateReserved": "2026-03-24T15:41:47.492Z",
"dateUpdated": "2026-03-26T15:02:49.257Z",
"state": "PUBLISHED"
},
"dataType": "CVE_RECORD",
"dataVersion": "5.2"
}
Mitigation MIT-4
Architecture and Design
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
Implementation
Architecture and Design
- 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
Architecture and Design
Implementation
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
Architecture and Design
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
Architecture and Design
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
Implementation
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
Implementation
With Struts, write all data from form beans with the bean's filter attribute set to true.
Mitigation MIT-31
Implementation
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
Implementation
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
Architecture and Design
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
Operation
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
Operation
Implementation
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.