Answer in brief
CVE-2026-86431 records a Medium severity (CVSS 6.9) vulnerability in commonmark before 2.9.1 XSS via AttributesExtension form feed bypass. The current sources do not mark it as known exploited. The current feed maps league/commonmark (composer), thephpleague/commonmark (generic), league/commonmark (packagist). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 6.9. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps league/commonmark (composer), thephpleague/commonmark (generic), league/commonmark (packagist). Check affected ranges and fixed versions before updating.
| Product | Affected versions | Fixed versions |
|---|---|---|
| cpe:2.3:a:thephpleague:commonmark:*:*:*:*:*:*:*:* | Not reported | Not reported |
| Package | Affected range | Fixed version |
|---|---|---|
| league/commonmarkcomposer | >=2.7.0,<2.9.1 | 2.9.1 |
| thephpleague/commonmarkgeneric | >=2.7.0 <2.9.1 | 2.9.1 |
| league/commonmarkpackagist | >=2.7.0 <2.9.1 | 2.9.1 |
Published upstream
Sep 7, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Oct 8, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Sep 1, 2026
league/commonmark (thephpleague/commonmark) versions >= 2.7.0 and < 2.9.1 contain a cross-site scripting vulnerability in the AttributesExtension. Prefixing an attribute name with a single U+000C form feed byte (e.g. {\x0Conclick="alert(1)"}) bypasses the AttributesHelper::filterAttributes() 'on*' event-handler filter because PHP's trim() does not strip U+000C, causing the attribute to be written verbatim into the output where browsers parse it as a genuine event handler. The same prefix also defeats the allow_unsafe_links check, allowing javascript: URIs through href/src attributes even when allow_unsafe_links is false. Exploitation requires processing untrusted Markdown with the AttributesExtension enabled; the injected script executes when the rendered HTML is viewed. Fixed in 2.9.1.
Quoted source text, attributed separately from HOL analysis.