{"id":"GHSA-8266-84wp-wv5c","summary":"Svelte has a potential mXSS vulnerability due to improper HTML escaping","details":"### Summary\n\nA potential XSS vulnerability exists in Svelte for versions prior to 4.2.19.\n\n### Details\n\nSvelte improperly escapes HTML on server-side rendering. It converts strings according to the following rules:\n\n- If the string is an attribute value:\n    - `\"` -\u003e `"`\n    - `&` -\u003e `&`\n    - Other characters -\u003e No conversion\n- Otherwise:\n    - `\u003c` -\u003e `<`\n    - `&` -\u003e `&`\n    - Other characters -\u003e No conversion\n\nThe assumption is that attributes will always stay as such, but in some situation the final DOM tree rendered on browsers is different from what Svelte expects on server-side rendering. This may be leveraged to perform XSS attacks. More specifically, this can occur when injecting malicious content into an attribute within a `\u003cnoscript\u003e` tag.\n\n### PoC\n\nA vulnerable page (`+page.svelte`):\n```html\n\u003cscript\u003e\nimport { page } from \"$app/stores\"\n\n// user input\nlet href = $page.url.searchParams.get(\"href\") ?? \"https://example.com\";\n\u003c/script\u003e\n\n\u003cnoscript\u003e\n  \u003ca href={href}\u003etest\u003c/a\u003e\n\u003c/noscript\u003e\n```\n\nIf a user accesses the following URL,\n```\nhttp://localhost:4173/?href=\u003c/noscript\u003e\u003cscript\u003ealert(123)\u003c/script\u003e\n```\nthen, `alert(123)` will be executed.\n\n### Impact\n\nXSS, when using an attribute within a noscript tag","aliases":["CVE-2024-45047"],"modified":"2024-08-30T20:01:23Z","published":"2024-08-30T16:49:10Z","database_specific":{"nvd_published_at":"2024-08-30T17:15:15Z","cwe_ids":["CWE-79"],"github_reviewed_at":"2024-08-30T16:49:10Z","severity":"MODERATE","github_reviewed":true},"references":[{"type":"WEB","url":"https://github.com/sveltejs/svelte/security/advisories/GHSA-8266-84wp-wv5c"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2024-45047"},{"type":"WEB","url":"https://github.com/sveltejs/svelte/commit/83e96e044deb5ecbae2af361ae9e31d3e1ac43a3"},{"type":"PACKAGE","url":"https://github.com/sveltejs/svelte"}],"affected":[{"package":{"name":"svelte","ecosystem":"npm","purl":"pkg:npm/svelte"},"ranges":[{"type":"SEMVER","events":[{"introduced":"0"},{"fixed":"4.2.19"}]}],"database_specific":{"source":"https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2024/08/GHSA-8266-84wp-wv5c/GHSA-8266-84wp-wv5c.json"}}],"schema_version":"1.7.3","severity":[{"type":"CVSS_V3","score":"CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N"},{"type":"CVSS_V4","score":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N"}]}