CVE-2026-9358: Postcss selector parser Denial of Service Vulnerability
LOWCVE-2026-9358 is a LOW (CVSS 4.3) denial of service vulnerability (CWE-404: Improper Resource Shutdown or Release) affecting Postcss selector parser libraries in the npm ecosystem. The issue involves postcss-selector-parser allows denial of service through uncontrolled ast recursion. Remediation is available by upgrading affected packages to version 6.1.3, 7.1.3.
CVE-2026-9358 at a Glance
Security Impact
CVSS: 4.3
The security impact metrics below are parsed directly from the CVSS v3.1 vector string (CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L).
How to Fix CVE-2026-9358
To remediate this vulnerability, upgrade all affected Postcss selector parser dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.
npm install postcss-selector-parser@6.1.3npm install postcss-selector-parser@7.1.3Run the following command in your project directory to verify that all resolved dependencies use the patched release:
npm ls postcss-selector-parserHow to Check if You Are Affected
To determine whether your Node.js application is affected by CVE-2026-9358, inspect your project dependencies using npm:
npm ls postcss-selector-parserAnalyze the terminal output to locate any version of Postcss selector parser in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 6.1.3), your application is affected.
Note: The npm ls postcss-selector-parser command inspects dependencies declared in your package.json and lockfile; it does not perform automated runtime dynamic scanning.
Technical Details
Vulnerability Mechanism & Technical Analysis
This vulnerability is classified under CWE-404: Improper Resource Shutdown or Release, where the product does not release or incorrectly releases a resource before it is made available for re-use. In Postcss selector parser, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.
Source Advisory Statement
CVE-2026-9358 Affected Postcss selector parser Versions
2 component(s)| Product / Package | Ecosystem | Affected Versions | Fixed Version |
|---|---|---|---|
|
postcss-selector-parser
|
npm |
≥ 6.1.0
< 6.1.3
|
6.1.3
|
|
postcss-selector-parser
|
npm |
≥ 7.1.0
< 7.1.3
|
7.1.3
|
References
Frequently Asked Questions
What is CVE-2026-9358?
Which Postcss selector parser versions are affected?
What version fixes CVE-2026-9358?
Is postcss-selector-parser affected?
What is the CVSS score of CVE-2026-9358?
What CWE is associated with CVE-2026-9358?
How can I check npm dependencies for CVE-2026-9358?
Machine-readable OSV JSON
OSV v1.5 Schema
{
"schema_version" : "1.4.0",
"id" : "GHSA-w9m9-85wc-3x92",
"modified" : "2026-09-01T15:45:54Z",
"published" : "2026-05-26T13:30:30Z",
"aliases" : [ "CVE-2026-9358" ],
"summary" : "postcss-selector-parser allows denial of service through uncontrolled AST recursion",
"details" : "A vulnerability was determined in postcss-selector-parser before 6.1.3 and 7.1.1. Affected is the function toString of the file src/selectors/container.js of the component AST Serialization. Executing a manipulation can lead to uncontrolled recursion. It is possible to launch the attack remotely. The exploit has been publicly disclosed and may be utilized. The vendor explains, that according to his definition \"DoS on server-side on user-generated CSS is low risk for us (since most users compile own CSS with PostCSS).\"",
"severity" : [ {
"type" : "CVSS_V3",
"score" : "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:L"
}, {
"type" : "CVSS_V4",
"score" : "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:P"
} ],
"affected" : [ {
"package" : {
"ecosystem" : "npm",
"name" : "postcss-selector-parser"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "6.1.0"
}, {
"fixed" : "6.1.3"
} ]
} ]
}, {
"package" : {
"ecosystem" : "npm",
"name" : "postcss-selector-parser"
},
"ranges" : [ {
"type" : "ECOSYSTEM",
"events" : [ {
"introduced" : "7.1.0"
}, {
"fixed" : "7.1.3"
} ]
} ]
} ],
"references" : [ {
"type" : "ADVISORY",
"url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-9358"
}, {
"type" : "WEB",
"url" : "https://github.com/postcss/postcss-selector-parser/commit/5bc698cef66f8abd12610dc623e5d67cbc0f869d"
}, {
"type" : "WEB",
"url" : "https://github.com/postcss/postcss-selector-parser/commit/e37c5b0b785b165e27508d2489fdec8e0f18b10a"
}, {
"type" : "WEB",
"url" : "https://gist.github.com/bx33661/581e3a38134601c04e19b4dfc9b459b9"
}, {
"type" : "PACKAGE",
"url" : "https://github.com/postcss/postcss-selector-parser"
}, {
"type" : "WEB",
"url" : "https://github.com/postcss/postcss-selector-parser/releases/tag/6.1.3"
}, {
"type" : "WEB",
"url" : "https://github.com/postcss/postcss-selector-parser/releases/tag/7.1.3"
}, {
"type" : "WEB",
"url" : "https://vuldb.com/cve/CVE-2026-9358"
}, {
"type" : "WEB",
"url" : "https://vuldb.com/submit/813080"
}, {
"type" : "WEB",
"url" : "https://vuldb.com/vuln/365321"
}, {
"type" : "WEB",
"url" : "https://vuldb.com/vuln/365321/cti"
} ],
"database_specific" : {
"cwe_ids" : [ "CWE-404" ],
"severity" : "LOW",
"github_reviewed" : true,
"github_reviewed_at" : "2026-09-01T15:45:53Z",
"nvd_published_at" : "2026-05-24T06:16:37Z"
}
}