Incomplete Denylist to Cross-Site Scripting Affecting league/commonmark package, versions >=1.5.0, <2.9.0
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-PHP-LEAGUECOMMONMARK-18600665
- published9 Aug 2026
- disclosed6 Aug 2026
- creditUnknown
Introduced: 6 Aug 2026
NewCVE-2026-71478 (opens in a new tab)How to fix?
Upgrade league/commonmark to version 2.9.0 or higher.
Overview
league/commonmark is a PHP-based Markdown parser which supports the full CommonMark spec. It is based on the CommonMark JS reference implementation.
Affected versions of this package are vulnerable to Incomplete Denylist to Cross-Site Scripting via the filterAttributes process. An attacker can execute arbitrary JavaScript in the context of the victim's browser by embedding control bytes within a javascript: URL in the href or src attribute, which bypasses the unsafe-link filter and is executed when a user interacts with the crafted link. This is only exploitable if the AttributesExtension is enabled and allow_unsafe_links is set to false.