{"description":"Trending threats, MITRE ATT\u0026CK coverage, and detection metadata. Fed continuously.","feed_url":"https://feed.craftedsignal.io/tags/postcss/feed.json","home_page_url":"https://feed.craftedsignal.io/","items":[{"_cs_actors":[],"_cs_cpes":[],"_cs_cves":[],"_cs_exploited":false,"_cs_has_poc":false,"_cs_poc_references":[],"_cs_products":["PostCSS (\u003c= 8.5.17)"],"_cs_severities":["high"],"_cs_tags":["path-traversal","information-disclosure","postcss","nodejs","ghsa"],"_cs_type":"advisory","_cs_vendors":[],"content_html":"\u003cp\u003eA significant path traversal vulnerability, identified as GHSA-r28c-9q8g-f849, has been discovered in PostCSS, a popular CSS processing tool, affecting versions up to 8.5.17. This flaw stems from the tool's default behavior of auto-detecting and attempting to load \u0026quot;previous source maps\u0026quot; specified in \u003ccode\u003e/*# sourceMappingURL=... */\u003c/code\u003e comments within CSS text. An attacker can manipulate these comments with directory traversal sequences (e.g., \u003ccode\u003e../../../\u003c/code\u003e) or absolute paths to bypass intended directory restrictions, coercing PostCSS into reading arbitrary \u003ccode\u003e.map\u003c/code\u003e files from the filesystem. If the application then returns the processed \u003ccode\u003eresult.map\u003c/code\u003e (a common practice in build pipelines), the attacker can extract sensitive information contained within the \u003ccode\u003esourcesContent\u003c/code\u003e field of these disclosed \u003ccode\u003e.map\u003c/code\u003e files. This vulnerability requires no authentication and can be triggered by submitting specially crafted CSS to any service that processes untrusted CSS with PostCSS without explicitly setting the \u003ccode\u003emap: false\u003c/code\u003e option.\u003c/p\u003e\n\u003ch2 id=\"attack-chain\"\u003eAttack Chain\u003c/h2\u003e\n\u003col\u003e\n\u003cli\u003eAn attacker identifies a service that accepts user-submitted CSS and processes it using PostCSS, leveraging its default \u003ccode\u003epostcss().process()\u003c/code\u003e behavior.\u003c/li\u003e\n\u003cli\u003eThe attacker crafts a malicious CSS input containing a \u003ccode\u003e/*# sourceMappingURL=../../../../some/other/app/dist/bundle.js.map */\u003c/code\u003e comment.\u003c/li\u003e\n\u003cli\u003eThe service invokes \u003ccode\u003epostcss().process()\u003c/code\u003e on the attacker's CSS, with the \u003ccode\u003emap\u003c/code\u003e option left at its default (true).\u003c/li\u003e\n\u003cli\u003eDuring processing, PostCSS's \u003ccode\u003eloadMap()\u003c/code\u003e function attempts to resolve the \u003ccode\u003esourceMappingURL\u003c/code\u003e annotation.\u003c/li\u003e\n\u003cli\u003eThe \u003ccode\u003epath.join()\u003c/code\u003e operation, combined with \u003ccode\u003eloadFile()\u003c/code\u003e, processes the traversal sequence, allowing access to \u003ccode\u003e.map\u003c/code\u003e files outside the intended directory.\u003c/li\u003e\n\u003cli\u003ePostCSS successfully reads the arbitrary \u003ccode\u003e.map\u003c/code\u003e file (e.g., \u003ccode\u003ebundle.js.map\u003c/code\u003e) from the server's filesystem.\u003c/li\u003e\n\u003cli\u003eThe \u003ccode\u003esourcesContent\u003c/code\u003e field from the read \u003ccode\u003e.map\u003c/code\u003e file, which often contains actual source code, is merged into the \u003ccode\u003eresult.map\u003c/code\u003e object generated by PostCSS.\u003c/li\u003e\n\u003cli\u003eThe vulnerable service, following typical build pipeline behavior, outputs or returns the \u003ccode\u003eresult.map\u003c/code\u003e to the attacker, leading to the disclosure of sensitive file contents.\u003c/li\u003e\n\u003c/ol\u003e\n\u003ch2 id=\"impact\"\u003eImpact\u003c/h2\u003e\n\u003cp\u003eThis vulnerability leads to the disclosure of contents from arbitrary \u003ccode\u003e.map\u003c/code\u003e files accessible by the PostCSS process's privileges on the filesystem. The impact is significant as \u003ccode\u003e.map\u003c/code\u003e files frequently contain embedded source code and project structure information which, if exposed, can reveal intellectual property, internal logic, or aid in further attacks. Any application processing untrusted CSS without explicitly disabling source map generation (via \u003ccode\u003emap: false\u003c/code\u003e) is vulnerable. No authentication or user interaction beyond submitting the malicious CSS is required. The specific number of victims is unknown, but given PostCSS's widespread use in web development, a large number of applications could be at risk.\u003c/p\u003e\n\u003ch2 id=\"recommendation\"\u003eRecommendation\u003c/h2\u003e\n\u003cul\u003e\n\u003cli\u003eUpgrade PostCSS to version 8.5.18 or later as soon as patches become available to remediate the path traversal vulnerability documented in GHSA-r28c-9q8g-f849.\u003c/li\u003e\n\u003cli\u003eFor immediate mitigation or if upgrading is not feasible, configure any application processing untrusted CSS with PostCSS to explicitly set the \u003ccode\u003emap: false\u003c/code\u003e option in the \u003ccode\u003epostcss().process()\u003c/code\u003e call. This prevents PostCSS from attempting to load source maps and nullifies the exploitation vector described in this brief.\u003c/li\u003e\n\u003cli\u003eReview the application's handling of \u003ccode\u003eresult.map\u003c/code\u003e to ensure that if source maps are legitimately generated, they are not inadvertently exposed to untrusted entities.\u003c/li\u003e\n\u003c/ul\u003e\n","date_modified":"2026-07-24T16:32:37Z","date_published":"2026-07-24T16:32:37Z","id":"https://feed.craftedsignal.io/briefs/2026-07-postcss-path-traversal-source-map/","summary":"A path traversal vulnerability (GHSA-r28c-9q8g-f849) in PostCSS versions up to 8.5.17 allows an unauthenticated attacker to disclose arbitrary `.map` file contents from a vulnerable server by crafting a `sourceMappingURL` comment in user-submitted CSS, leading to sensitive information exposure if the processed output is returned.","title":"PostCSS Path Traversal Vulnerability via Source Map Auto-Loading","url":"https://feed.craftedsignal.io/briefs/2026-07-postcss-path-traversal-source-map/"}],"language":"en","title":"CraftedSignal Threat Feed - Postcss","version":"https://jsonfeed.org/version/1.1"}