{"answers":{"affected":"2 open source packages ship an affected version, including league/commonmark. It affects 1 product.","exploited":"There is no known exploitation of CVE-2026-86431 in the wild and no public exploit code.","fix":"Upgrade league/commonmark to 2.9.1 or later.","what":"CVE-2026-86431 is a medium-severity cross-site scripting vulnerability in thephpleague commonmark, published on 7 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim."},"fix_prompt":"Check this codebase for CVE-2026-86431 and fix it if it is affected.\n\nWhat it is: CVE-2026-86431 is a medium-severity cross-site scripting vulnerability in thephpleague commonmark, published on 7 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.\nExploitation: There is no known exploitation of CVE-2026-86431 in the wild and no public exploit code.\n\nAffected packages and fixed versions:\n- league/commonmark (Packagist): affected from 2.7.0; fixed in 2.9.1\n- league/commonmark (Packagist): affected from 2.7.0; fixed in 2.9.1\n\nTask:\n1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.\n2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.\n3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.\n4. Run the tests and summarise what changed and why.\n5. If nothing in the project is affected, say so and change nothing.\n\nReference: https://insights.sbomify.com/CVE-2026-86431/ (Markdown: https://insights.sbomify.com/CVE-2026-86431/index.md)","id":"CVE-2026-86431","markdown":"https://insights.sbomify.com/CVE-2026-86431/index.md","name":"CVE-2026-86431","record":{"aliases":["DEBIAN-CVE-2026-86431","GHSA-f8fg-pg57-v4j8","GHSA-m24x-mf52-x8gc","UBUNTU-CVE-2026-86431"],"analysis":{"component_type":"library","fix_type":"upgrade","impacts":["code_execution"],"network_reachable":"yes","non_default_config":true,"product_category":"PHP Markdown library","requires_auth":"none","summary":"Attackers can inject malicious scripts into rendered HTML by bypassing attribute filters in the commonmark library's AttributesExtension.","user_interaction":"not_required","vuln_class":"xss"},"analysis_generated_by":"qwen3.8-flash-next","assigner":"VulnCheck","cpe":[{"product":"commonmark","vendor":"thephpleague"}],"cvss":{"score":6.9,"severity":"medium","source":"cna","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:N/SC:L/SI:L/SA:N","version":"4.0"},"cwes":[{"id":"CWE-79","name":"Improper Neutralization of Input During Web Page Generation"}],"description":"league/commonmark (thephpleague/commonmark) versions \u003e= 2.7.0 and \u003c 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.","ecosystems":["Packagist"],"exploits":{"exploitdb":0,"first_seen":null,"github_poc":0,"max_poc_stars":null,"metasploit":0,"nuclei":0,"refs":[],"tier":"none_known"},"has_fix":true,"headline":"commonmark before 2.9.1 XSS via AttributesExtension form feed bypass","id":"CVE-2026-86431","indexable":true,"kev":null,"kind":"cve","links":{"ecosystem":"Packagist","product":null,"products":[],"type":"xss","year":"2026"},"n_packages":2,"n_references":3,"next":{"headline":"commonmark 2.0.0 before 2.8.4 Denial of Service via XML","id":"CVE-2026-86432"},"packages":[{"ecosystem":"Packagist","fixed":["2.9.1"],"introduced":["2.7.0"],"last_affected":[],"package":"league/commonmark","purl":null,"source":"GHSA-f8fg-pg57-v4j8"},{"ecosystem":"Packagist","fixed":["2.9.1"],"introduced":["2.7.0"],"last_affected":[],"package":"league/commonmark","purl":"pkg:composer/league/commonmark","source":"GHSA-f8fg-pg57-v4j8"}],"prev":{"headline":"league/commonmark before 2.9.1 Denial of Service via parsing","id":"CVE-2026-86430"},"products":["commonmark"],"published":"2026-09-07","related":[{"cvss_score":8.7,"headline":"commonmark 1.5.0 before 2.10.0 Denial of Service via Attributes","id":"CVE-2026-86428","kev_date_added":null,"published":"2026-09-07"},{"cvss_score":8.7,"headline":"commonmark before 2.9.1 Denial of Service via SmartPunct and Attributes","id":"CVE-2026-86429","kev_date_added":null,"published":"2026-09-07"},{"cvss_score":8.7,"headline":"league/commonmark before 2.9.1 Denial of Service via parsing","id":"CVE-2026-86430","kev_date_added":null,"published":"2026-09-07"},{"cvss_score":6.3,"headline":"league/commonmark has an embed extension allowed_domains bypass","id":"CVE-2026-33347","kev_date_added":null,"published":"2026-03-24"},{"cvss_score":6.1,"headline":"Moderate severity vulnerability that affects league/commonmark","id":"CVE-2019-10010","kev_date_added":null,"published":"2019-03-24"},{"cvss_score":6.1,"headline":"PHP League CommonMark vulnerable to Cross-Site Scripting (XSS)","id":"CVE-2018-20583","kev_date_added":null,"published":"2018-12-30"}],"sources":[{"class":"attribution","licence":"CVE Terms of Use (MITRE)","name":"CVE List","prefix":"CVE"},{"class":"attribution","licence":"CC BY 4.0","name":"GitHub Advisory Database","prefix":"GHSA"},{"class":"attribution","licence":"US public information, NVD API terms","name":"NVD"},{"class":"attribution","licence":"CWE Terms of Use","name":"CWE (MITRE)"},{"class":"attribution","licence":"FIRST CVSS licence","name":"CVSS (FIRST)"}],"ssvc":{"automatable":"yes","exploitation":"none","technical_impact":"partial"},"state":"PUBLISHED","updated":"2026-10-08","vendors":["thephpleague"]},"summary":"Attackers can inject malicious scripts into rendered HTML by bypassing attribute filters in the commonmark library's AttributesExtension.","url":"https://insights.sbomify.com/CVE-2026-86431/"}