CVE-2026-91928 Overview
CVE-2026-91928 is a cross-site scripting (XSS) vulnerability in the Apache Sling XSS module. The flaw stems from improper neutralization of input during web page generation [CWE-79]. Attackers can inject malicious script content that executes in the context of a victim's browser session. The vulnerability affects all versions of Apache Sling XSS prior to 2.4.12. Apache has released version 2.4.12 to remediate the issue.
Critical Impact
Successful exploitation allows attackers to execute arbitrary JavaScript in the victim's browser, potentially leading to session hijacking, credential theft, or unauthorized actions on behalf of authenticated users. Exploitation requires user interaction, such as clicking a crafted link.
Affected Products
- Apache Sling XSS versions prior to 2.4.12
- Applications built on the Apache Sling framework using the XSS protection module
- Downstream content management platforms relying on Apache Sling for input sanitization
Discovery Timeline
- 2026-09-23 - CVE-2026-91928 published to the National Vulnerability Database (NVD)
- 2026-09-23 - Last updated in NVD database
Technical Details for CVE-2026-91928
Vulnerability Analysis
The Apache Sling XSS module provides encoding and validation utilities intended to prevent script injection in generated web content. CVE-2026-91928 identifies a deficiency in how the module neutralizes untrusted input before it is rendered into HTML output. Attacker-controlled data can bypass the sanitization logic and reach the browser as executable script content.
The vulnerability is network-exploitable and requires user interaction, such as visiting a crafted URL or opening a malicious page. Successful exploitation crosses a security boundary because the injected script executes within the trust context of the vulnerable application. Impact is limited to confidentiality and integrity of user-accessible data; availability is not directly affected.
Root Cause
The root cause is improper neutralization of input during web page generation [CWE-79]. The org.apache.sling.xss library fails to correctly encode or filter specific input constructs before they are embedded in HTML output. Applications that rely on the module's protective filters to sanitize user-supplied data inherit the flaw.
Attack Vector
An attacker crafts input containing script payloads that evade the sanitizer in Apache Sling XSS. The attacker then delivers a link or content reference to a target user. When the victim loads the affected page, the browser parses and executes the injected script under the origin of the vulnerable application. Consult the Apache Mailing List Thread and Openwall OSS-Security Discussion for technical details.
Detection Methods for CVE-2026-91928
Indicators of Compromise
- HTTP requests containing script tags, javascript: URIs, or event handler attributes such as onerror= and onload= in parameters processed by Sling applications
- Unexpected outbound requests from user browsers to attacker-controlled domains following visits to Sling-hosted content
- Web server access logs showing repeated probing of Sling endpoints with encoded payloads such as %3Cscript%3E variants
Detection Strategies
- Inventory deployed Apache Sling XSS module versions and flag any release earlier than 2.4.12
- Deploy web application firewall (WAF) rules that inspect request parameters for common XSS payload patterns targeting Sling-based applications
- Correlate anomalous JavaScript execution in browser telemetry with server-side request logs to identify reflected or stored XSS activity
Monitoring Recommendations
- Enable verbose logging on Sling request processing pipelines to capture parameter values that trigger sanitizer edge cases
- Monitor Content Security Policy (CSP) violation reports for blocked inline script execution originating from Sling-rendered pages
- Track authenticated session anomalies such as unexpected privilege changes or session token reuse from new IP addresses
How to Mitigate CVE-2026-91928
Immediate Actions Required
- Upgrade the Apache Sling XSS module to version 2.4.12 or later across all deployments
- Audit applications that depend on org.apache.sling.xss to confirm they consume the patched artifact
- Review recent web logs for evidence of exploitation attempts targeting Sling-based endpoints
Patch Information
Apache has released Apache Sling XSS version 2.4.12, which fixes the improper neutralization issue. Users are recommended to upgrade to this version. Refer to the Apache Mailing List Thread for the official announcement and coordinate downstream dependency updates in Maven or Gradle build configurations.
Workarounds
- Deploy a strict Content Security Policy (CSP) that disallows inline scripts and restricts script sources to trusted origins
- Apply WAF signatures that block common XSS payload patterns in requests to Sling-based applications until patching is complete
- Restrict access to content authoring interfaces to trusted users to reduce the attack surface for stored XSS scenarios
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
