GHSA-7fh5-64p2-3v2j CVE-2023-44270

PostCSS line return parsing error

Medium npm

Severity: 5.3 / 10; Medium · CVSS 3.1
Exploit chance (EPSS): 0.97%; Chance of exploitation in the next 30 days. Higher than 62.03% of scored vulnerabilities.
Known exploited: No; Not in CISA's catalog
Weakness: CWE-74 Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection'); CWE-144 Improper Neutralization of Line Delimiters
Fix: 8.4.31; Upgrade postcss to this version or later

Description

An issue was discovered in PostCSS before 8.4.31. It affects linters using PostCSS to parse external Cascading Style Sheets (CSS). There may be \r discrepancies, as demonstrated by @font-face{ font:(\r/*);} in a rule.

This vulnerability affects linters using PostCSS to parse external untrusted CSS. An attacker can prepare CSS in such a way that it will contains parts parsed by PostCSS as a CSS comment. After processing by PostCSS, it will be included in the PostCSS output in CSS nodes (rules, properties) despite being originally included in a comment.

Affected versions

npm

Package	Vulnerable	Fixed in
postcss	`< 8.4.31`	`8.4.31`
postcss	`< 8.4.31`	`8.4.31`

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.

postcss npm → `8.4.31`

npm

npm install postcss@8.4.31

yarn

yarn add postcss@8.4.31

pnpm

pnpm add postcss@8.4.31

Severity breakdown

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-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

The product constructs all or part of a command, data structure, or record using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify how it is parsed or interpreted when it is sent to a downstream component.

How to prevent it

Requirements: Programming languages and supporting technologies might be chosen which are not subject to these issues.
Implementation: Utilize an appropriate mix of allowlist and denylist parsing to filter control-plane syntax from all input.

CWE-144: Improper Neutralization of Line Delimiters

The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could be interpreted as line delimiters when they are sent to a downstream component.

How to prevent it

Developers should anticipate that line delimiters will be injected/removed/manipulated in the input vectors of their product. Use an appropriate combination of denylists and allowlists to ensure only valid, expected and appropriate input is processed by the system.
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.
Implementation: While it is risky to use dynamically-generated query strings, code, or commands that mix control and data together, sometimes it may be unavoidable. Properly quote arguments and escape any special characters within those arguments. The most conservative approach is to escape or filter all characters that do not pass an extremely strict allowlist (such as everything that is not alphanumeric or white space). If some special characters are still needed, such as white space, wrap each argument in quotes after the escaping/filtering step. Be careful of argument injection (CWE-88).
Implementation: Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174). Such errors could be used to bypass allowlist validation schemes by introducing dangerous inputs after they have been checked.

References

Advisories

Fixes and patches

github.com/postcss/postcss/commit/58cc860b4c1707510c9cd1bc1fa30b423a9ad6c5

Packages

github.com/postcss/postcss

Timeline

Sep 29, 2023 Published
Sep 10, 2026 Last updated by the source
Oct 31, 2026 Latest EPSS score

Advisory	Severity	Why it's related
GHSA-fxqj-rqcc-2cmp PostCSS: incomplete fix of GHSA-6g55-p6wh-862q — attacker-controlled sourceMappingURL reads arbitrary .map files when `from` is unset	Medium	Also affects postcss
GHSA-r28c-9q8g-f849 PostCSS: Path Traversal in Previous Source Map Auto-Loading (sourceMappingURL) leads to Arbitrary .map File Disclosure	High	Also affects postcss
GHSA-6g55-p6wh-862q PostCSS: Arbitrary file read and information disclosure via attacker-controlled sourceMappingURL in CSS comments	Critical	Also affects postcss
GHSA-qx2v-qp2m-jg93 PostCSS has XSS via Unescaped </style> in its CSS Stringify Output	Medium	Also affects postcss
GHSA-566m-qj78-rww5 Regular Expression Denial of Service in postcss	High	Also affects postcss
GHSA-hwj9-h5mp-3pm3 Regular Expression Denial of Service in postcss	Medium	Also affects postcss
GHSA-j8rh-479h-cp32 Axios: Header Injection via Inherited headers After Minimal Interceptor	Medium	Same weakness, CWE-74
GHSA-4hqw-qxg8-jxx2 Axios: Fetch Adapter Header Injection via Inherited FormData getHeaders	Medium	Same weakness, CWE-74

Credits: DCKcode

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