CVE-2026-103864 in Sling Engine
Summary
by MITRE • 11/05/2026
Improper output neutralization for logs in Apache Sling Engine.
This issue affects Apache Sling Engine: before 3.0.4.
Users are recommended to upgrade to version 3.0.4, which fixes the issue.
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Analysis
by VulDB Data Team • 11/05/2026
The vulnerability identified as improper output neutralization for logs within the Apache Sling Engine represents a significant security risk related to log injection and potential server-side request forgery or cross-site scripting depending on how the logs are consumed. This flaw exists in versions of Apache Sling Engine prior to 3.0.4, where user-supplied input is written directly into application log files without adequate sanitization or encoding. In many web applications, logging mechanisms serve as a critical component for auditing and debugging, but they can also become an attack vector if the data being logged contains special characters that are not properly escaped. When these logs are subsequently viewed through a web interface, parsed by another system, or processed in a way that interprets the content as code rather than plain text, the injected payloads can be executed by the victim's browser or interpreted maliciously by downstream systems.
The technical root cause of this vulnerability lies in the failure to apply appropriate output encoding when writing data to log files. Specifically, characters such as angle brackets, quotes, and ampersands that have special meaning in HTML or other markup languages are passed through without transformation. This allows an attacker who controls input parameters—such as URL query strings, HTTP headers, or form fields—to inject arbitrary content into the logs. For instance, if a user submits a crafted string containing JavaScript code via a request parameter, and this parameter is logged verbatim by Sling Engine, that malicious script becomes part of the log entry. If an administrator later views these logs through a web-based logging dashboard that does not perform its own output encoding, the embedded script will execute in their browser session. This scenario aligns with CWE-117, which describes Improper Output Neutralization for Logs, and often intersects with CWE-79, known as Cross-Site Scripting (XSS), particularly when the logs are rendered in a web context without proper encoding.
From an operational perspective, the impact of this vulnerability extends beyond simple data corruption or log pollution. Successful exploitation can lead to session hijacking if cookies are accessible via script execution within the logging interface. It may also facilitate phishing attacks against system administrators by displaying malicious content that appears legitimate due to its origin in trusted application logs. Furthermore, attackers might use this vector to exfiltrate sensitive information stored in sessions or headers into log files that could be accessed by other users with lower privileges if file permissions are misconfigured. The ATT&CK framework categorizes such techniques under T1059, Command and Scripting Interpreter, specifically when the logged content is interpreted as executable code, or potentially under data exfiltration tactics if sensitive data is written to accessible log files for later retrieval by an attacker with read access to those logs.
Mitigation strategies primarily involve upgrading the Apache Sling Engine to version 3.0.4 or any subsequent release where this issue has been resolved. The fix typically involves implementing strict output encoding on all user-supplied data before it is written to log files, ensuring that special characters are converted into their safe HTML entity equivalents or otherwise neutralized so they cannot be interpreted as executable code by downstream consumers of the logs. In addition to upgrading software organizations should review any custom logging implementations within Sling-based applications to ensure consistent application of encoding standards such as OWASP ESAPI guidelines for log injection prevention. Regular security audits and static analysis tools can help identify similar patterns in legacy codebases where input validation is applied at entry points but output neutralization is neglected during the logging phase, thereby closing this specific attack surface effectively.