Reject alias-bomb YAML front matter before parsing#26
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YAML front matter is parsed with Yaml::parse(), which resolves anchors and aliases. A few hundred bytes of aliased YAML (a "billion laughs" bomb) expands exponentially: parsing stays cheap, but ParserOutput serializes the result into the parser cache, materializing the full expansion and exhausting memory uncatchably -- reachable by any editor, since Markdown is the default content model everywhere. Add a FrontMatterGuard that inspects only the raw block (never a parsed structure, so its cost stays bounded by the input size) and rejects front matter that uses more than a handful of anchor/alias markers or exceeds a generous size ceiling. Rejected front matter is treated as absent and stripped from the body. Legitimate metadata -- including & and * inside plain scalars and the occasional single-anchor reuse -- still parses unchanged. Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Codecov Report✅ All modified and coverable lines are covered by tests. Additional details and impacted files@@ Coverage Diff @@
## master #26 +/- ##
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+ Coverage 82.37% 82.76% +0.39%
- Complexity 314 323 +9
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Files 33 34 +1
Lines 834 853 +19
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+ Hits 687 706 +19
Misses 147 147 ☔ View full report in Codecov by Harness. 🚀 New features to boost your workflow:
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Authored with Claude Code (
claude-opus-4-8 (max)), directed by Jeroen. Closes a denial-of-service vector in YAML front matter:Yaml::parse()resolves anchors and aliases, so a few hundred bytes of aliased YAML (a "billion laughs" bomb) expands exponentially — parsing stays cheap, butParserOutputserializes the result into the parser cache, materializing the full expansion and exhausting memory uncatchably (reachable by any editor, since Markdown is the default content model everywhere). AFrontMatterGuardinspects only the raw block (never a parsed structure, so its cost stays bounded by input size) and rejects front matter that uses more than a handful of anchor/alias markers — including aliases pinned against a quoted key's colon in JSON-style flow mappings — or exceeds a generous size ceiling; the exact rejected block is stripped so nothing leaks into the body. Legitimate metadata (including&/*inside plain scalars and the occasional single-anchor reuse) still parses unchanged.