Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessAuthenticate as privileged content author
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DeliverySubmit HTML with whitespace-obfuscated data: URI
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ExploitBypass InputFilter cleanAttribute sanitization
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ExecutionStore payload in content
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PersistVictim views page, script executes in their session
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ImpactHijack session or act as victim
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A05:2025 - Injection
ASVS 5.0
V1 - Encoding and Sanitization Output encoding, context-aware escaping
MITRE ATT&CK
2 techniques across 2 tactics: Initial Access, Execution The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | Exploitation requires an authenticated account with high enough privilege to submit HTML content that is processed by Joomla's InputFilter (PR:H), such as a content author/editor role, and requires a victim to subsequently view the stored content (UI:P). The specific trigger is an HTML data: URI in an attribute value padded with whitespace characters that circumvent the cleanAttribute cleanup routine. Limiting factors: it is not exploitable by anonymous/unauthenticated users, it depends on the victim rendering the injected content, and it affects only Joomla CMS 1.5.0-5.4.8 / 6.0.0-6.1.3 and the joomla_framework_filter_package; sites restricting HTML-authoring privileges are materially less exposed. |
| Impact | This is a stored XSS filter bypass in Joomla's InputFilter (cleanAttribute), which is meant to strip dangerous HTML data: URIs but can be evaded with injected whitespace. The vendor CVSS 4.0 vector (AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:L) scores 7.1 and, notably, carries the exploit-maturity metric E:P, indicating the vendor considers a proof-of-concept level of exploitability to exist - though no standalone POC link is provided in the intelligence. The vector's PR:H means exploitation requires an authenticated, high-privilege content author, and UI:P means a victim must view the injected content, both of which meaningfully constrain real-world abuse versus a drive-by unauthenticated XSS. There is NO CISA KEV listing and NO EPSS score in the provided data, so there is no evidence of active or widespread exploitation; this reads as a real-but-bounded issue rather than an urgent internet-wide threat. The vendor's VC:H/VI:H (high confidentiality/integrity) is more aggressive than a typical XSS rating and reflects worst-case session/admin-account compromise; an independent CVSS 3.1 assessment lands lower (~6.9, C:L/I:L). Key gap to verify: the CVSS 4.0 vector supplies no SSVC automatable/technical-impact fields and no NVD 3.1 vector, so exploitation-status confidence rests solely on the vendor's E:P maturity flag. |
| Exploit ScenarioDerived | An authenticated Joomla user with content-authoring privileges submits an article or HTML field containing an HTML data: URI padded with whitespace characters that slip past InputFilter's cleanAttribute sanitization. When a victim - typically an administrator or another user - views the stored content, the malicious script executes in their browser session. The vendor's E:P (proof-of-concept) exploit-maturity flag suggests demonstration code for the bypass technique is known, though no public POC link is provided. |
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Alert meAnalysisAIv1 – Sep 29, 2026
Stored cross-site scripting (XSS) in Joomla CMS allows an authenticated user with HTML-authoring privileges - such as a content author or editor - to slip HTML data: URIs past the InputFilter::cleanAttribute routine by padding them with whitespace characters, so the payload survives sanitisation and executes in the browser of any victim who later views the stored content. Affected releases are Joomla CMS 1.5.0 through 5.4.8 and 6.0.0 through 6.1.3, along with the standalone joomla_framework_filter_package. There is no CISA KEV listing, so this is not confirmed actively exploited, and no public exploit code was identified in the supplied intelligence, although the vendor-assigned CVSS 4.0 vector does carry an exploit-maturity rating of Proof-of-Concept (E:P); the issue is not exploitable anonymously and depends on a victim rendering the injected content.
RemediationAI
Apply the fixed release documented in the Joomla Security Centre advisory for this issue (https://developer.joomla.org/security-centre/1096-20260916-core-xss-filter-bypass-in-inputfilter-via-whitespace-characters-in-html-data-uris.html); patch status is best described as "Patch available per vendor advisory", since no exact fixed version number is stated in the available data - treat the current maintenance release in the Joomla 5.x/6.x line as the target and confirm the precise version in the advisory. If the site runs a long end-of-life branch (1.5 through 4.x) for which no upgrade path is offered, the most effective compensating control is to remove HTML-authoring rights from untrusted accounts, because the flaw requires an authenticated user who can submit HTML that is processed by InputFilter; restricting HTML editing to a small set of trusted editors materially reduces exposure, at the cost of editorial flexibility. Additional stopgaps, to be treated as temporary and evasion-prone, include a WAF or reverse-proxy rule that rejects or normalises attribute values containing data: URIs broken up by whitespace characters, and disabling rich-text/HTML input paths for untrusted roles. Any application embedding the separately distributed joomla_framework_filter_package must be updated independently of the CMS, and because the payload is stored, remediation should also include scanning and cleansing previously submitted article, custom-field, and module content for injected data: URIs.
Affected VersionsENISA
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 2 packages in euvd
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
This is a CWE-79 improper-neutralisation-of-input-during-web-page-generation flaw rooted in Joomla's InputFilter class, specifically the cleanAttribute() method that is responsible for stripping dangerous URI schemes - including HTML data: URIs - from attribute values during HTML cleaning. Because the cleanup matches the data: scheme literally, an attacker who inserts whitespace characters into the attribute value can evade the blacklist while browsers, which are tolerant of such whitespace when parsing attribute values, still resolve and execute the resulting data: URI. The vulnerable logic ships both in Joomla CMS core and in the separately distributed joomla_framework_filter_package, which is why the supplied CPE data lists both cpe:2.3:a:joomla!_project:joomla!_cms and cpe:2.3:a:joomla!_project:joomla!_framework_filter_package; those CPE strings are version-agnostic wildcards, so the concrete version boundaries come from the vendor description rather than the CPE dictionary. This is filter-evasion rather than a memory-safety or server-side injection primitive, and its severity derives from the trust that every extension and template places in InputFilter to neutralise dangerous markup on the site's behalf.
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Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:P/VC:H/VI:H/VA:L/SC:N/SI:N/SA:N/E:P
Stored XSS reachable by an authenticated content submitter (PR:L, though vendor chose PR:H for HTML-authoring roles), needing victim view (UI:R) and executing in the victim's context (S:C), typical XSS C:L/I:L.
Primary rating from Vendor (Joomla).
CVSS VectorVendor: Joomla
DescriptionCVE.org
Joomla! Core - [20260916] - Core - XSS filter bypass in InputFilter via whitespace characters in HTML data URIs in Joomla 1.5.0-5.4.8, 6.0.0-6.1.3 - The cleanAttribute method removes HTML data URIs, however injected whitespaces characters could circumvent that cleanup, causing an XSS vector.
Executive ViewAI
Joomla CMS versions 1.5.0 through 5.4.8 and 6.0.0 through 6.1.3, plus the standalone joomla_framework_filter_package, contain a stored cross-site scripting flaw that lets content authors or editors with HTML-authoring privileges slip malicious data: URIs past input sanitization. Visitors who later view the affected content may have their browser sessions compromised, credentials phished, or pages defaced, creating reputational, operational, and compliance risk for any organization hosting these Joomla releases. No vendor-released patch identified at time of analysis, and no public exploit identified at time of analysis.
No vendor-released patch identified at time of analysis. Interim mitigations include restricting HTML-authoring privileges to trusted users, reviewing and sanitizing stored content for whitespace-obfuscated data: URIs, disabling or filtering data: URI rendering through WAF or virtual patching, monitoring for stored XSS payloads, applying least privilege to content author and editor roles, and tracking Joomla advisories for versions 1.5.0 through 5.4.8, 6.0.0 through 6.1.3, and the standalone joomla_framework_filter_package.
Threat Intelligence Overview
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Cross-Site Scripting occurs when an application accepts untrusted data and sends it to a web browser without proper validation or encoding.
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EUVD-2026-89073
GHSA-943m-2293-5c6p
NVD
CVE.org
EPSS
Vulnrichment
Exploit-DB