CVE-2021-27671 is a medium-severity (CVSS 6.1) Cross-site Scripting (XSS) vulnerability in comrak. A fix is available for comrak — see the affected versions and patch details below.
Cross site scripting in comrak
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
comrakReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
An issue was discovered in the comrak crate before 0.9.1 for Rust. Cross site scripting (XSS) can occur because the protection mechanism for data: and javascript: URIs is case-sensitive, allowing (for example) Data: to be used in an attack.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | comrak | all versions | 0.9.1cargo update -p comrak --precise 0.9.1 |
Affected Products
comrakcomrak_projectDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for comrak, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update comrak to 0.9.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-27671 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2021-27671 in your dependencies?
Find it across crates.io, including transitive dependencies.