CVE-2026-46637
Twig: HTML-output filters in twig/* extras incorrectly declared `is_safe => ['all']`
Description
### Description Several 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. Affected filters: - `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><img src=x onerror=alert(1)></code>` becomes `` `<img src=x onerror=alert(1)>` ``, which renders live when interpolated into an HTML page. - `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). - `inline_css` (`twig/cssinliner-extra`) emits HTML with inlined styles. Same constraint as `markdown_to_html`. In 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. ### Resolution - `html_to_markdown` no longer claims to be safe in any escaping context; its plain-text output is now autoescaped for the surrounding context. - `markdown_to_html` and `inline_css` are now declared `is_safe => ['html']`, asserting only what they actually guarantee. ### Credits Twig 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`.
Affected packages (3)
- Debian/php-twigfrom 0
- Packagist/twig/cssinliner-extrafrom 0, < 3.26.0
- Packagist/twig/markdown-extrafrom 0, < 3.26.0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 4.0 | — | CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:N/SC:L/SI:L/SA:N/E:U |
References (6)
- ADVISORYhttps://security-tracker.debian.org/tracker/CVE-2026-46637
- PATCHhttps://github.com/twigphp/Twig
- WEBhttps://github.com/FriendsOfPHP/security-advisories/blob/master/twig/cssinliner-extra/CVE-2026-46637.yaml
- WEBhttps://github.com/FriendsOfPHP/security-advisories/blob/master/twig/markdown-extra/CVE-2026-46637.yaml
- WEBhttps://github.com/twigphp/Twig/security/advisories/GHSA-jv8m-2544-3pg3
- WEBhttps://symfony.com/cve-2026-46637