What is CVE-2026-71478?
league/commonmark is a PHP library for parsing and rendering CommonMark Markdown. From 1.5.0 until 2.9.0, the AttributesExtension's href and src unsafe-link filter can be bypassed by embedding control bytes, such as a tab, carriage return, line feed, or leading C0 control character, in a javascript: URL that browsers discard before parsing the scheme, causing the browser to still execute the script even when the unsafe-link filter is enabled. This issue is fixed in 2.9.0.
The record classifies CVE-2026-71478 under weakness classes CWE-79, CWE-86, CWE-692. Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs no prior authentication, needs a user to take an action first. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 60 days ago.
Severity and exploitation probability
- CVSS v3.1 base score
- 6.1 — MEDIUM
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N - EPSS (FIRST)
- 0.2% probability of exploitation in the next 30 days, higher than 10.0% of all scored CVEs
- CISA KEV
- Not listed in the CISA Known Exploited Vulnerabilities catalog
- Threadlinqs priority
- 3.5/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- Published
- 2026-08-06, last modified 2026-08-07
Is CVE-2026-71478 being exploited?
It currently carries a trending score of 32 in the Threadlinqs vulnerability feed.
Affected products and versions
- thephpleague: commonmark
Affected software packages:
composer:league/commonmark— patched in 2.9.0
How to fix CVE-2026-71478
Fixed versions are recorded for 1 package: composer:league/commonmark 2.9.0. No vendor patch reference has been recorded for CVE-2026-71478 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.
Threat activity tracking CVE-2026-71478
No threat campaign in the Threadlinqs corpus currently references CVE-2026-71478, in its CVE list or as an indicator. The linkage is recomputed from the live corpus on every daily ingest, so this section fills in as soon as a tracked campaign cites the identifier.
Sources
Enriched from CVE.org, FIRST EPSS, GitHub Security Advisories, NVD. Last verified by Threadlinqs on . This product uses the NVD API but is not endorsed or certified by the NVD.