GHSA-4fh9-h7wg-q85m CVE-2025-66400
mdast-util-to-hast has unsanitized class attribute
Medium
npm
- Severity
- 6.9 / 10
- Medium · CVSS 4.0
- Exploit chance (EPSS)
- 0.33%
- Chance of exploitation in the next 30 days. Higher than 25.77% of scored vulnerabilities.
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-20 Improper Input Validation
- CWE-915 Improperly Controlled Modification of Dynamically-Determined Object Attributes
- Fix
13.2.1- Upgrade mdast-util-to-hast to this version or later
Description
Impact
Multiple (unprefixed) classnames could be added in markdown source by using character references.
This could make rendered user supplied markdown code elements appear like the rest of the page.
The following markdown:
```js xss
```
Would create <pre><code class="language-js xss"></code></pre>
If your page then applied .xss classes (or listeners in JS), those apply to this element.
For more info see https://github.com/ChALkeR/notes/blob/master/Improper-markup-sanitization.md#unsanitized-class-attribute
Patches
The bug was patched. When using regular semver, run npm install. For exact ranges, make sure to use 13.2.1.
Workarounds
Update.
References
Affected versions
npm
| Package | Vulnerable | Fixed in |
|---|---|---|
| mdast-util-to-hast | >= 13.0.0, < 13.2.1 |
13.2.1 |
| mdast-util-to-hast | >= 13.0.0, < 13.2.1 |
13.2.1 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
mdast-util-to-hast npm → 13.2.1
- npm
npm install mdast-util-to-hast@13.2.1- yarn
yarn add mdast-util-to-hast@13.2.1- pnpm
pnpm add mdast-util-to-hast@13.2.1
Severity breakdown
CVSS 4.0 6.9
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N
- Attack vector
- Network
- Attack complexity
- Low
- Attack requirements
- None
- Privileges required
- None
- User interaction
- None
- Confidentiality (vulnerable system)
- None
- Integrity (vulnerable system)
- Low
- Availability (vulnerable system)
- None
- Confidentiality (subsequent systems)
- None
- Integrity (subsequent systems)
- None
- Availability (subsequent systems)
- None
CVSS 3.1 5.3
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
- Attack vector
- Network
- Attack complexity
- Low
- Privileges required
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- Low
- Availability
- None
Weakness
CWE-20: Improper Input Validation
The product receives input or data, but it does not validate or incorrectly validates that the input has the properties that are required to process the data safely and correctly.
How to prevent it
- Architecture and Design: Consider using language-theoretic security (LangSec) techniques that characterize inputs using a formal language and build "recognizers" for that language. This effectively requires parsing to be a distinct layer that effectively enforces a boundary between raw input and internal data representations, instead of allowing parser code to be scattered throughout the program, where it could be subject to errors or inconsistencies that create weaknesses. [REF-1109] [REF-1110] [REF-1111]
- Architecture and Design: Use an input validation framework such as Struts or the OWASP ESAPI Validation API. Note that using a framework does not automatically address all input validation problems; be mindful of weaknesses that could arise from misusing the framework itself (CWE-1173).
- Architecture and Design, Implementation: Understand all the potential areas where untrusted inputs can enter the product, including but not limited to: 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.
- Implementation: 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.
- 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. Even though client-side checks provide minimal benefits with respect to server-side security, they are still useful. First, they can support intrusion detection. If the server receives input that should have been rejected by the client, then it may be an indication of an attack. Second, client-side error-checking can provide helpful feedback to the user about the expectations for valid input. Third, there may be a reduction in server-side processing time for accidental input errors, although this is typically a small savings.
- Implementation: When your application combines data from multiple sources, perform the validation after the sources have been combined. The individual data elements may pass the validation step but violate the intended restrictions after they have been combined.
- Implementation: Be especially careful to validate all input when invoking code that crosses language boundaries, such as from an interpreted language to native code. This could create an unexpected interaction between the language boundaries. Ensure that you are not violating any of the expectations of the language with which you are interfacing. For example, even though Java may not be susceptible to buffer overflows, providing a large argument in a call to native code might trigger an overflow.
- Implementation: Directly convert your input type into the expected data type, such as using a conversion function that translates a string into a number. After converting to the expected data type, ensure that the input's values fall within the expected range of allowable values and that multi-field consistencies are maintained.
- Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180, CWE-181). Make sure that your application does not inadvertently decode the same input twice (CWE-174). Such errors could be used to bypass allowlist schemes by introducing dangerous inputs after they have been checked. Use libraries such as the OWASP ESAPI Canonicalization control. Consider performing repeated canonicalization until your input does not change any more. This will avoid double-decoding and similar scenarios, but it might inadvertently modify inputs that are allowed to contain properly-encoded dangerous content.
- Implementation: 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.
CWE-915: Improperly Controlled Modification of Dynamically-Determined Object Attributes
The product receives input from an upstream component that specifies multiple attributes, properties, or fields that are to be initialized or updated in an object, but it does not properly control which attributes can be modified.
How to prevent it
- Implementation: If available, use features of the language or framework that allow specification of allowlists of attributes or fields that are allowed to be modified. If possible, prefer allowlists over denylists. For applications written with Ruby on Rails, use the attr_accessible (allowlist) or attr_protected (denylist) macros in each class that may be used in mass assignment.
- Architecture and Design, Implementation: If available, use the signing/sealing features of the programming language to assure that deserialized data has not been tainted. For example, a hash-based message authentication code (HMAC) could be used to ensure that data has not been modified.
- Implementation: For any externally-influenced input, check the input against an allowlist of internal object attributes or fields that are allowed to be modified.
- Implementation, Architecture and Design: Refactor the code so that object attributes or fields do not need to be dynamically identified, and only expose getter/setter functionality for the intended attributes.
References
Advisories
Fixes and patches
Packages
Timeline
- Published
- Last updated by the source
- Latest EPSS score
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-m665-v7pm-7grj zip: Critical Parser Differential & Security Control Bypass via Dual-Header Inconsistencies (Zip Cloaking) Leading to Arbitrary File Overwrite & RCE | Critical | Same weakness, CWE-20 |
| GHSA-g5ff-637f-6q2m LiteLLM: internal_user_viewer arbitrary local file read via `vertex_ai_credentials` | High | Same weakness, CWE-20 |
| GHSA-h3rc-j82p-2c3h vLLM: Untrusted EPS inputs can trigger denial of service or Ghostscript RCE | High | Same weakness, CWE-20 |
| GHSA-8c8m-p3m8-cjg8 Nodemailer: A nested comment ends early in addressparser, releasing the rest of the comment as a recipient | Medium | Same weakness, CWE-20 |
| GHSA-m943-m63m-w62w Nodemailer: A ";" inside a quoted string or comment ends an address group early in addressparser, turning display text into a recipient | Medium | Same weakness, CWE-20 |
| GHSA-85x2-q946-cp5h Nodemailer: A ">" inside a quoted local part ends an angle-addr early in addressparser, delivering to a domain the header does not name | Medium | Same weakness, CWE-20 |
| GHSA-5hx5-vpf9-5wcv pypdf: Unvalidated JPEG image data loading | Low | Same weakness, CWE-20 |
| GHSA-wjr9-j795-jxcr fast-uri vulnerable to host confusion via unchecked WHATWG host canonicalization | Medium | Same weakness, CWE-20 |
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