CVE-2025-54812 in Log4cxx
Summary
by MITRE • 08/22/2025
Improper Output Neutralization for Logs vulnerability in Apache Log4cxx.
When using HTMLLayout, logger names are not properly escaped when writing out to the HTML file. If untrusted data is used to retrieve the name of a logger, an attacker could theoretically inject HTML or Javascript in order to hide information from logs or steal data from the user. In order to activate this, the following sequence must occur:
* Log4cxx is configured to use HTMLLayout.
* Logger name comes from an untrusted string
* Logger with compromised name logs a message
* User opens the generated HTML log file in their browser, leading to potential XSS
Because logger names are generally constant strings, we assess the impact to users as LOW
This issue affects Apache Log4cxx: before 1.5.0.
Users are recommended to upgrade to version 1.5.0, which fixes the issue.
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Analysis
by VulDB Data Team • 11/03/2025
The CVE-2025-54812 vulnerability represents an improper output neutralization for logs issue within Apache Log4cxx that specifically impacts the HTMLLayout functionality. This vulnerability stems from insufficient sanitization of logger names when generating HTML log files, creating potential security risks for systems that utilize this logging mechanism. The flaw exists in the way the logging framework handles logger identification strings during HTML output generation, where special characters are not properly escaped or filtered before being written to log files. This technical oversight allows for potential cross-site scripting attacks when users open the generated HTML log files in web browsers.
The operational impact of this vulnerability becomes apparent when considering the specific conditions required for exploitation. Attackers must first ensure that Log4cxx is configured to use HTMLLayout, which is not the default setting in most deployments. Additionally, the vulnerability requires that logger names originate from untrusted input sources, such as user-provided data or external APIs. When these conditions align, an attacker can inject malicious HTML or JavaScript code into logger names, which then gets embedded in the generated HTML log files. The actual execution of the malicious code occurs when unsuspecting users open these log files in web browsers, potentially leading to session hijacking, data theft, or other browser-based attacks.
This vulnerability aligns with CWE-116, which specifically addresses improper output neutralization for logs, and demonstrates characteristics consistent with ATT&CK technique T1566.001 for initial access through spearphishing attachments. The risk assessment categorizes this issue as low impact primarily because logger names are typically static string literals in most applications rather than dynamic user inputs. However, the vulnerability remains exploitable in scenarios where dynamic logger naming is implemented, particularly in applications that accept user-provided identifiers for logging purposes. The attack vector requires user interaction to open the malicious HTML log file, which provides a natural defense mechanism but does not eliminate the security concern entirely.
The recommended mitigation strategy involves upgrading to Apache Log4cxx version 1.5.0 or later, which includes proper output neutralization for logger names in HTMLLayout implementations. Organizations should also conduct configuration reviews to ensure that HTMLLayout is only enabled when necessary and that logger naming practices avoid incorporating untrusted data. Security teams should monitor for any applications that might be using dynamic logger names from external sources and implement proper input validation and sanitization measures. Additionally, regular security testing should include verification of logging configurations and output formats to prevent similar vulnerabilities from emerging in other components of the logging infrastructure. The fix implemented in version 1.5.0 addresses the core issue by ensuring that all logger identifiers are properly escaped when written to HTML output, preventing the injection of malicious content that could compromise user sessions or data confidentiality.