CWE-116
Allowed-with-ReviewImproper Encoding or Escaping of Output
Abstraction: Class · Status: Draft
The product prepares a structured message for communication with another component, but encoding or escaping of the data is either missing or done incorrectly. As a result, the intended structure of the message is not preserved.
614 vulnerabilities reference this CWE, most recent first.
GHSA-XRJ6-CWW5-QM75
Vulnerability from github – Published: 2022-10-04 00:00 – Updated: 2022-10-06 00:00phpipam v1.5.0 was discovered to contain a header injection vulnerability via the component /admin/subnets/ripe-query.php.
{
"affected": [],
"aliases": [
"CVE-2022-41443"
],
"database_specific": {
"cwe_ids": [
"CWE-116"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2022-10-03T16:15:00Z",
"severity": "CRITICAL"
},
"details": "phpipam v1.5.0 was discovered to contain a header injection vulnerability via the component /admin/subnets/ripe-query.php.",
"id": "GHSA-xrj6-cww5-qm75",
"modified": "2022-10-06T00:00:57Z",
"published": "2022-10-04T00:00:23Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2022-41443"
},
{
"type": "WEB",
"url": "https://gist.github.com/enferas/7acd9636cc221bbf61d51425ab91ef01"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
"type": "CVSS_V3"
}
]
}
GHSA-XVP8-3MHV-424C
Vulnerability from github – Published: 2026-03-02 19:35 – Updated: 2026-03-05 22:49Summary
The <base> tag passes through the default Cleaner configuration. While page_structure=True removes html, head, and title tags, there is no specific handling for <base>, allowing an attacker to inject it and hijack relative links on the page.
Details
The <base> tag is not currently in the page_structure kill set. Even though the specification says <base> must be inside <head>, browsers accept <base> tags outside of the head.
If an attacker injects a <base> tag, it changes the base URL for all relative URLs on the page (links, images, scripts) to a domain controlled by the attacker.
PoC
from lxml_html_clean import clean_html
# The base tag is preserved in the output
result = clean_html('<base href="http://evil.com/"><a href="/account">Account</a>')
print(result)
# Output: <div><base href="http://evil.com/">...<a href="/account">Account</a></div>
Impact
The injection of a <base> tag allows an attacker to hijack the resolution of all relative URLs on the page. This results in three critical attack vectors:
- Phishing & Redirection: Attackers can redirect user navigation (e.g.,
<a href="/login">) and form submissions (e.g.,<form action="/auth">) to an attacker-controlled domain, effectively stealing credentials or sensitive data without the user realizing they have left the legitimate site. - Cross-Site Scripting (XSS): If the victim application loads JavaScript files using relative paths (e.g.,
<script src="assets/app.js">), the browser will attempt to fetch the script from the attacker's domain. This upgrades the vulnerability from HTML injection to full Stored XSS. - Defacement: Relative references to images (
<img>) and stylesheets (<link>) will be loaded from the attacker's server, allowing for UI redressing or defacement.
{
"affected": [
{
"database_specific": {
"last_known_affected_version_range": "\u003c= 0.4.3"
},
"package": {
"ecosystem": "PyPI",
"name": "lxml-html-clean"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "0.4.4"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2026-28350"
],
"database_specific": {
"cwe_ids": [
"CWE-116"
],
"github_reviewed": true,
"github_reviewed_at": "2026-03-02T19:35:52Z",
"nvd_published_at": "2026-03-05T20:16:16Z",
"severity": "MODERATE"
},
"details": "### Summary\nThe `\u003cbase\u003e` tag passes through the default `Cleaner` configuration. While `page_structure=True` removes `html`, `head`, and `title` tags, there is no specific handling for `\u003cbase\u003e`, allowing an attacker to inject it and hijack relative links on the page.\n\n### Details\nThe `\u003cbase\u003e` tag is not currently in the `page_structure` kill set. Even though the specification says `\u003cbase\u003e` must be inside `\u003chead\u003e`, browsers accept `\u003cbase\u003e` tags outside of the head.\n\nIf an attacker injects a `\u003cbase\u003e` tag, it changes the base URL for all relative URLs on the page (links, images, scripts) to a domain controlled by the attacker.\n\n### PoC\n```python\nfrom lxml_html_clean import clean_html\n\n# The base tag is preserved in the output\nresult = clean_html(\u0027\u003cbase href=\"http://evil.com/\"\u003e\u003ca href=\"/account\"\u003eAccount\u003c/a\u003e\u0027)\nprint(result)\n# Output: \u003cdiv\u003e\u003cbase href=\"http://evil.com/\"\u003e...\u003ca href=\"/account\"\u003eAccount\u003c/a\u003e\u003c/div\u003e\n```\n\n### Impact\nThe injection of a `\u003cbase\u003e` tag allows an attacker to hijack the resolution of **all** relative URLs on the page. This results in three critical attack vectors:\n\n1. **Phishing \u0026 Redirection:** Attackers can redirect user navigation (e.g., `\u003ca href=\"/login\"\u003e`) and form submissions (e.g., `\u003cform action=\"/auth\"\u003e`) to an attacker-controlled domain, effectively stealing credentials or sensitive data without the user realizing they have left the legitimate site.\n2. **Cross-Site Scripting (XSS):** If the victim application loads JavaScript files using relative paths (e.g., `\u003cscript src=\"assets/app.js\"\u003e`), the browser will attempt to fetch the script from the attacker\u0027s domain. This upgrades the vulnerability from HTML injection to full Stored XSS.\n3. **Defacement:** Relative references to images (`\u003cimg\u003e`) and stylesheets (`\u003clink\u003e`) will be loaded from the attacker\u0027s server, allowing for UI redressing or defacement.",
"id": "GHSA-xvp8-3mhv-424c",
"modified": "2026-03-05T22:49:24Z",
"published": "2026-03-02T19:35:52Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/fedora-python/lxml_html_clean/security/advisories/GHSA-xvp8-3mhv-424c"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2026-28350"
},
{
"type": "WEB",
"url": "https://github.com/fedora-python/lxml_html_clean/commit/9c5612ca33b941eec4178abf8a5294b103403f34"
},
{
"type": "PACKAGE",
"url": "https://github.com/fedora-python/lxml_html_clean"
}
],
"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"
}
],
"summary": "lxml-html-clean has \u003cbase\u003e tag injection through default Cleaner configuration"
}
GHSA-XW2R-F8XV-C8XP
Vulnerability from github – Published: 2023-08-09 14:37 – Updated: 2023-08-09 14:37Impact
xss injection through isCleanHTML method
Patches
1.7.8.10 8.0.5 8.1.1
Found by
Aleksey Solovev (Positive Technologies)
Workarounds
References
{
"affected": [
{
"package": {
"ecosystem": "Packagist",
"name": "prestashop/prestashop"
},
"ranges": [
{
"events": [
{
"introduced": "8.1.0"
},
{
"fixed": "8.1.1"
}
],
"type": "ECOSYSTEM"
}
],
"versions": [
"8.1.0"
]
},
{
"package": {
"ecosystem": "Packagist",
"name": "prestashop/prestashop"
},
"ranges": [
{
"events": [
{
"introduced": "8.0.0"
},
{
"fixed": "8.0.5"
}
],
"type": "ECOSYSTEM"
}
]
},
{
"package": {
"ecosystem": "Packagist",
"name": "prestashop/prestashop"
},
"ranges": [
{
"events": [
{
"introduced": "0"
},
{
"fixed": "1.7.8.10"
}
],
"type": "ECOSYSTEM"
}
]
}
],
"aliases": [
"CVE-2023-39527"
],
"database_specific": {
"cwe_ids": [
"CWE-116"
],
"github_reviewed": true,
"github_reviewed_at": "2023-08-09T14:37:16Z",
"nvd_published_at": "2023-08-07T21:15:10Z",
"severity": "HIGH"
},
"details": "### Impact\nxss injection through `isCleanHTML` method\n\n### Patches\n1.7.8.10\n8.0.5\n8.1.1\n\n### Found by\nAleksey Solovev (Positive Technologies)\n\n### Workarounds\n\n### References\n",
"id": "GHSA-xw2r-f8xv-c8xp",
"modified": "2023-08-09T14:37:16Z",
"published": "2023-08-09T14:37:16Z",
"references": [
{
"type": "WEB",
"url": "https://github.com/PrestaShop/PrestaShop/security/advisories/GHSA-xw2r-f8xv-c8xp"
},
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2023-39527"
},
{
"type": "WEB",
"url": "https://github.com/PrestaShop/PrestaShop/commit/afc14f8eaa058b3e6a20ac43e033ee2656fb88b4"
},
{
"type": "PACKAGE",
"url": "https://github.com/PrestaShop/PrestaShop"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:H/A:H",
"type": "CVSS_V3"
}
],
"summary": "PrestaShop XSS injection through Validate::isCleanHTML method"
}
GHSA-XWC2-PV6J-7344
Vulnerability from github – Published: 2025-03-19 06:31 – Updated: 2025-03-19 06:31Improper encoding or escaping of output vulnerability in the webapi component in Synology BeeStation Manager (BSM) before 1.1-65374, Synology DiskStation Manager (DSM) before 6.2.4-25556-8, 7.1.1-42962-7, 7.2-64570-4, 7.2.1-69057-6 and 7.2.2-72806-1 and Synology Unified Controller (DSMUC) before 3.1.4-23079 allows remote attackers to read limited files via unspecified vectors.
{
"affected": [],
"aliases": [
"CVE-2024-50629"
],
"database_specific": {
"cwe_ids": [
"CWE-116"
],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-03-19T06:15:15Z",
"severity": "MODERATE"
},
"details": "Improper encoding or escaping of output vulnerability in the webapi component in Synology BeeStation Manager (BSM) before 1.1-65374, Synology DiskStation Manager (DSM) before 6.2.4-25556-8, 7.1.1-42962-7, 7.2-64570-4, 7.2.1-69057-6 and 7.2.2-72806-1 and Synology Unified Controller (DSMUC) before 3.1.4-23079 allows remote attackers to read limited files via unspecified vectors.",
"id": "GHSA-xwc2-pv6j-7344",
"modified": "2025-03-19T06:31:54Z",
"published": "2025-03-19T06:31:54Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2024-50629"
},
{
"type": "WEB",
"url": "https://www.synology.com/en-global/security/advisory/Synology_SA_24_20"
},
{
"type": "WEB",
"url": "https://www.synology.com/en-global/security/advisory/Synology_SA_24_23"
}
],
"schema_version": "1.4.0",
"severity": [
{
"score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N",
"type": "CVSS_V3"
}
]
}
Mitigation MIT-4.3
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.
- For example, consider using the ESAPI Encoding control [REF-45] or a similar tool, library, or framework. These will help the programmer encode outputs in a manner less prone to error.
- Alternately, use built-in functions, but consider using wrappers in case those functions are discovered to have a vulnerability.
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.
- For example, stored procedures can enforce database query structure and reduce the likelihood of SQL injection.
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.
Mitigation
In some cases, input validation may be an important strategy when output encoding is not a complete solution. For example, you may be providing the same output that will be processed by multiple consumers that use different encodings or representations. In other cases, you may be required to allow user-supplied input to contain control information, such as limited HTML tags that support formatting in a wiki or bulletin board. When this type of requirement must be met, use an extremely strict allowlist to limit which control sequences can be used. Verify that the resulting syntactic structure is what you expect. Use your normal encoding methods for the remainder of the input.
Mitigation
Use input validation as a defense-in-depth measure to reduce the likelihood of output encoding errors (see CWE-20).
Mitigation
Fully specify which encodings are required by components that will be communicating with each other.
Mitigation
When exchanging data between components, ensure that both components are using the same character encoding. Ensure that the proper encoding is applied at each interface. Explicitly set the encoding you are using whenever the protocol allows you to do so.
CAPEC-104: Cross Zone Scripting
An attacker is able to cause a victim to load content into their web-browser that bypasses security zone controls and gain access to increased privileges to execute scripting code or other web objects such as unsigned ActiveX controls or applets. This is a privilege elevation attack targeted at zone-based web-browser security.
CAPEC-73: User-Controlled Filename
An attack of this type involves an adversary inserting malicious characters (such as a XSS redirection) into a filename, directly or indirectly that is then used by the target software to generate HTML text or other potentially executable content. Many websites rely on user-generated content and dynamically build resources like files, filenames, and URL links directly from user supplied data. In this attack pattern, the attacker uploads code that can execute in the client browser and/or redirect the client browser to a site that the attacker owns. All XSS attack payload variants can be used to pass and exploit these vulnerabilities.
CAPEC-81: Web Server Logs Tampering
Web Logs Tampering attacks involve an attacker injecting, deleting or otherwise tampering with the contents of web logs typically for the purposes of masking other malicious behavior. Additionally, writing malicious data to log files may target jobs, filters, reports, and other agents that process the logs in an asynchronous attack pattern. This pattern of attack is similar to "Log Injection-Tampering-Forging" except that in this case, the attack is targeting the logs of the web server and not the application.
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.