{"id":"CVE-2026-46637","aliases":["GHSA-jv8m-2544-3pg3"],"url":"https://o3.security/vulnerability/CVE-2026-46637","summary":"Twig: HTML-output filters in twig/* extras incorrectly declared `is_safe => ['all']`","details":"### Description\n\nSeveral filters in the `twig/*` extras packages are registered with `is_safe => ['all']`, which tells Twig's autoescaper to treat their output as safe in every context (`html`, `js`, `css`, `url`, ...). The output of these filters is plain text or HTML markup, neither of which is safe in every escaping context.\n\nAffected filters:\n\n- `html_to_markdown` (`twig/markdown-extra`) emits plain Markdown text. `league/html-to-markdown` decodes HTML entities when producing code spans and fenced blocks, so an attacker-controlled `<code>&lt;img src=x onerror=alert(1)&gt;</code>` becomes `` `<img src=x onerror=alert(1)>` ``, which renders live when interpolated into an HTML page.\n- `markdown_to_html` (`twig/markdown-extra`) emits HTML. Safe in an HTML context but not in JS, CSS or URL contexts (e.g. when interpolated into an inline `<script>` block).\n- `inline_css` (`twig/cssinliner-extra`) emits HTML with inlined styles. Same constraint as `markdown_to_html`.\n\nIn all three cases, `is_safe => ['all']` causes the autoescaper to emit the output verbatim in any context, even when the developer never wrote `|raw`. In a context such as a JS string or a URL parameter, this produces unescaped HTML and is exploitable as XSS.\n\n### Resolution\n\n- `html_to_markdown` no longer claims to be safe in any escaping context; its plain-text output is now autoescaped for the surrounding context.\n- `markdown_to_html` and `inline_css` are now declared `is_safe => ['html']`, asserting only what they actually guarantee.\n\n### Credits\n\nTwig would like to thank Claude Mythos Preview (via Project Glasswing) for reporting the issue and providing the fix for `html_to_markdown` and `markdown_to_html` in `twig/markdown-extra`, and Christophe Coevoet for extending the audit to `inline_css` in `twig/cssinliner-extra`.","published":"2026-07-14T21:25:20.141Z","modified":"2026-08-12T03:51:30.391618696Z","cvss":null,"epss":{"score":0.00305,"percentile":0.23236,"asOf":"2026-09-16"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"Packagist","name":"twig/markdown-extra","fixedVersion":"3.26.0"},{"ecosystem":"Packagist","name":"twig/cssinliner-extra","fixedVersion":"3.26.0"}],"fix":{"url":"https://github.com/twigphp/Twig/commit/84982072c79a7417b0d158a401d91344f3658299","label":"twigphp/Twig@8498207"},"references":[{"type":"WEB","url":"https://github.com/twigphp/Twig/releases/tag/v3.26.0"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/46xxx/CVE-2026-46637.json"},{"type":"ADVISORY","url":"https://github.com/twigphp/Twig/security/advisories/GHSA-jv8m-2544-3pg3"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2026-46637"},{"type":"FIX","url":"https://github.com/twigphp/Twig/commit/84982072c79a7417b0d158a401d91344f3658299"},{"type":"FIX","url":"https://github.com/twigphp/Twig/commit/e36489d3521ecbfc08bdcc61294302557035f14a"},{"type":"WEB","url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/twig/cssinliner-extra/CVE-2026-46637.yaml"},{"type":"WEB","url":"https://github.com/FriendsOfPHP/security-advisories/blob/master/twig/markdown-extra/CVE-2026-46637.yaml"},{"type":"PACKAGE","url":"https://github.com/twigphp/Twig"},{"type":"WEB","url":"https://symfony.com/cve-2026-46637"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-08-12T03:51:30.391618696Z"}}