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`.
How to fix CVE-2026-46637
To remediate CVE-2026-46637, upgrade the affected package to a fixed version below.
- —no fix listed
- —upgrade to 3.26.0 or later
- —upgrade to 3.26.0 or later
Is CVE-2026-46637 being exploited?
No exploitation signal available. Neither CISA KEV nor a current EPSS score has been published for CVE-2026-46637.