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PostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. Versions prior to 8.5.10 do not escape `</style>` sequences when stringifying CSS ASTs. When user-submitted CSS is parsed and re-stringified for embedding in HTML `<style>` tags, `</style>` in CSS values breaks out of the style context, enabling XSS. Version 8.5.10 fixes the issue.
Read the publisher's advisoryPostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. Versions prior to 8.5.10 do not escape `</style>` sequences when stringifying CSS ASTs. When user-submitted CSS is parsed and re-stringified for embedding in HTML `<style>` tags, `</style>` in CSS values breaks out of the style context, enabling XSS. Version 8.5.10 fixes the issue.
Read the publisher's advisoryPostCSS takes a CSS file and provides an API to analyze and modify its rules by transforming the rules into an Abstract Syntax Tree. Versions prior to 8.5.10 do not escape `</style>` sequences when stringifying CSS ASTs. When user-submitted CSS is parsed and re-stringified for embedding in HTML `<style>` tags, `</style>` in CSS values breaks out of the style context, enabling XSS. Version 8.5.10 fixes the issue.
Read the publisher's advisory# PostCSS: XSS via Unescaped `</style>` in CSS Stringify Output ## Summary PostCSS v8.5.5 (latest) does not escape `</style>` sequences when stringifying CSS ASTs. When user-submitted CSS is parsed and re-stringified for embedding in HTML `<style>` tags, `</style>` in CSS values breaks out of the style context, enabling XSS. ## Proof of Concept ```javascript const postcss = require('postcss'); // Parse user CSS and re-stringify for page embedding const userCSS = 'body { content: "</style><script>alert(1)</script><style>"; }'; const ast = postcss.parse(userCSS); const output = ast.toResult().css; const html = `<style>${output}</style>`; console.log(html); // <style>body { content: "</style><script>alert(1)</script><style>"; }</style> // // Browser: </style> closes the style tag, <script> executes ``` **Tested output** (Node.js v22, postcss v8.5.5): ``` Input: body { content: "</style><script>alert(1)</script><style>"; } Output: body { content: "</style><script>alert(1)</script><style>"; } Contains </style>: true ``` ## Impact Impact non-bundler use cases since bundlers for XSS on their own. Requires some PostCSS plugin to have malware code, which can inject XSS to website. ## Suggested Fix Escape `</style` in all stringified output values: ```javascript output = output.replace(/<\/(style)/gi, '<\\/$1'); ``` ## Credits Discovered and reported by [Sunil Kumar](https://tharvid.in) ([@TharVid](https://github.com/TharVid))
Read the publisher's advisoryVendor product
Shown as published. These rules are not interpreted as NuGet package version ranges.
{
"vendor": "postcss",
"product": "postcss",
"versions": [
{
"version": "< 8.5.10",
"status": "affected"
}
]
}Original source record · Cite this exact observation · Complete original publisher JSON
EUVD source date text has no stated timezone and is retained without inventing a UTC instant. Related bulletin membership is not an alias, common cause or applicability claim. A missing vector with a zero score is treated as unrated. Complete vendor/product and underlying source evidence remains in the original JSON.
datePublished: Apr 24, 2026, 2:27:47 AM
dateUpdated: Apr 24, 2026, 4:23:41 PM
msrc_CVE-2026-41305: PostCSS has XSS via Unescaped </style> in its CSS Stringify Output
CVE-2026-41305
RHSA-2026:56431: Red Hat Security Advisory: Red Hat OpenShift Data Foundation 4.18.27 security, enhancement & bug fix update
CVE-2025-61726 · CVE-2025-61729 · CVE-2025-64718 · CVE-2025-68470 · CVE-2026-1525 · CVE-2026-1526 · CVE-2026-1527 · CVE-2026-2229 · CVE-2026-6321 · CVE-2026-6322 · CVE-2026-6733 · CVE-2026-6734 · CVE-2026-9358 · CVE-2026-9679 · CVE-2026-9697 · CVE-2026-11525 · CVE-2026-12143 · CVE-2026-12151 · CVE-2026-13149 · CVE-2026-13676 · CVE-2026-22036 · CVE-2026-25645 · CVE-2026-33186 · CVE-2026-33349 · CVE-2026-33671 · CVE-2026-33672 · CVE-2026-33750 · CVE-2026-34043 · CVE-2026-34986 · CVE-2026-35469 · CVE-2026-39821 · CVE-2026-40181 · CVE-2026-41305 · CVE-2026-41650 · CVE-2026-41907 · CVE-2026-42342 · CVE-2026-45409 · CVE-2026-45736 · CVE-2026-48779 · CVE-2026-48801 · CVE-2026-53550 · CVE-2026-59869
WID-SEC-W-2026-1654: IBM App Connect Enterprise: Mehrere Schwachstellen
CVE-2021-23337 · CVE-2026-27141 · CVE-2026-4800 · CVE-2026-33750 · CVE-2026-40186 · CVE-2026-40895 · CVE-2026-41305 · CVE-2026-41650 · CVE-2026-42264 · CVE-2026-41242
WID-SEC-W-2026-3046: IBM Concert: Mehrere Schwachstellen
CVE-2019-19921 · CVE-2021-23337 · CVE-2024-3651 · CVE-2024-39338 · CVE-2024-45590 · CVE-2025-13465 · CVE-2025-15284 · CVE-2025-15599 · CVE-2025-22874 · CVE-2025-47273 · CVE-2025-47907 · CVE-2025-52881 · CVE-2025-53643 · CVE-2025-55184 · CVE-2025-58056 · CVE-2025-58188 · CVE-2025-58189 · CVE-2025-61723 · CVE-2025-61730 · CVE-2025-64649 · CVE-2025-64756 · CVE-2025-67221 · CVE-2025-68121 · CVE-2025-68146 · CVE-2026-0540 · CVE-2026-2327 · CVE-2026-23490 · CVE-2026-23897 · CVE-2026-2391 · CVE-2026-23949 · CVE-2026-24486 · CVE-2026-25528 · CVE-2026-25547 · CVE-2026-25639 · CVE-2026-25990 · CVE-2026-26007 · CVE-2026-26019 · CVE-2026-26996 · CVE-2026-27142 · CVE-2026-27212 · CVE-2026-27699 · CVE-2026-27903 · CVE-2026-27904 · CVE-2026-28684 · CVE-2026-29063 · CVE-2026-29181 · CVE-2026-2950 · CVE-2026-31808 · CVE-2026-31900 · CVE-2026-32274 · CVE-2026-32288 · CVE-2026-32597 · CVE-2026-32630 · CVE-2026-32887 · CVE-2026-32952 · CVE-2026-33186 · CVE-2026-33532 · CVE-2026-33750 · CVE-2026-33814 · CVE-2026-33816 · CVE-2026-33916 · CVE-2026-34043 · CVE-2026-34073 · CVE-2026-34077 · CVE-2026-3520 · CVE-2026-35469 · CVE-2026-35515 · CVE-2026-3627 · CVE-2026-39823 · CVE-2026-39825 · CVE-2026-39826 · CVE-2026-39892 · CVE-2026-39984 · CVE-2026-40175 · CVE-2026-40179 · CVE-2026-40181 · CVE-2026-40190 · CVE-2026-40347 · CVE-2026-41066 · CVE-2026-41182 · CVE-2026-41238 · CVE-2026-41239 · CVE-2026-41240 · CVE-2026-41305 · CVE-2026-41324 · CVE-2026-41425 · CVE-2026-41481 · CVE-2026-41488 · CVE-2026-41602 · CVE-2026-41636 · CVE-2026-42151 · CVE-2026-42154 · CVE-2026-42198 · CVE-2026-42211 · CVE-2026-42338 · CVE-2026-42342 · CVE-2026-42561 · CVE-2026-42577 · CVE-2026-43870 · CVE-2026-44405 · CVE-2026-44431 · CVE-2026-44432 · CVE-2026-44486 · CVE-2026-44487 · CVE-2026-44488 · CVE-2026-44492 · CVE-2026-44494 · CVE-2026-44496 · CVE-2026-44728 · CVE-2026-4539 · CVE-2026-45409 · CVE-2026-45736 · CVE-2026-46625 · CVE-2026-4800 · CVE-2026-4923 · CVE-2026-4926 · CVE-2026-7246 · CVE-2026-8723
RHSA-2026:56928: Red Hat Security Advisory: Red Hat OpenShift Data Foundation 4.22.2 security, enhancement & bug fix update
CVE-2026-6321 · CVE-2026-6322 · CVE-2026-9358 · CVE-2026-33671 · CVE-2026-33672 · CVE-2026-33750 · CVE-2026-40181 · CVE-2026-41305 · CVE-2026-41650 · CVE-2026-41907 · CVE-2026-42338 · CVE-2026-44665 · CVE-2026-45149 · CVE-2026-45736
RHSA-2026:86618: Red Hat Security Advisory: New container image: rhceph-9.2
CVE-2023-46159 · CVE-2024-47866 · CVE-2024-48916 · CVE-2024-55565 · CVE-2025-12816 · CVE-2025-15599 · CVE-2025-26791 · CVE-2025-30156 · CVE-2025-50181 · CVE-2025-50182 · CVE-2025-58754 · CVE-2025-59343 · CVE-2025-62718 · CVE-2025-66030 · CVE-2025-66035 · CVE-2025-66412 · CVE-2025-69873 · CVE-2026-0540 · CVE-2026-21441 · CVE-2026-22610 · CVE-2026-25639 · CVE-2026-26996 · CVE-2026-27903 · CVE-2026-27904 · CVE-2026-27970 · CVE-2026-32141 · CVE-2026-33228 · CVE-2026-33671 · CVE-2026-33672 · CVE-2026-33891 · CVE-2026-33894 · CVE-2026-33895 · CVE-2026-33896 · CVE-2026-39865 · CVE-2026-40175 · CVE-2026-40895 · CVE-2026-41238 · CVE-2026-41239 · CVE-2026-41240 · CVE-2026-41305 · CVE-2026-42033 · CVE-2026-42034 · CVE-2026-42035 · CVE-2026-42036 · CVE-2026-42037 · CVE-2026-42038 · CVE-2026-42039 · CVE-2026-42040 · CVE-2026-42041 · CVE-2026-42042 · CVE-2026-42043 · CVE-2026-42044 · CVE-2026-50152 · CVE-2026-58224
No normalized affected-package data is projected for this source revision. The original publisher record may contain additional product and version evidence; this does not establish that a package is unaffected.
Original source record · Cite this exact observation · Complete original publisher JSON
NVD analysis and CPE criteria are source context, not proof that a package or your environment is affected. Complete affected data, logical configurations and SSVC are retained in the original JSON.
Source analysis status: Deferred
Weakness classifications: CWE-79
published: 2026-04-24T03:16:11.547
lastModified: 2026-06-17T10:46:28.700
No normalized affected-package data is projected for this source revision. The original publisher record may contain additional product and version evidence; this does not establish that a package is unaffected.
Original source record · Cite this exact observation · Complete original publisher JSON
npm
SEMVER · introduced 0 → fixed 8.5.10
Original source record · Cite this exact observation · Complete original publisher JSON