CVE-2012-1102 in Perl
Summary
by MITRE • 07/09/2021
It was discovered that the XML::Atom Perl module before version 0.39 did not disable external entities when parsing XML from potentially untrusted sources. This may allow attackers to gain read access to otherwise protected resources, depending on how the library is used.
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Analysis
by VulDB Data Team • 08/19/2026
The vulnerability identified in versions of the XML::Atom Perl module prior to release 0.39 centers on a critical failure to disable external entity processing during the parsing of Extensible Markup Language data. This flaw allows for what is commonly known as an XML External Entity injection, or XXE attack vector. When applications utilize this library to parse XML documents originating from untrusted sources, such as user inputs, web service responses, or file uploads, they inadvertently permit the inclusion and resolution of external entities defined within the document structure. In standard XML processing, external entities are references that point to resources outside the immediate document, which can include local files on the server's filesystem, remote URLs, or other network-accessible services. By failing to explicitly disable this feature, the library exposes the underlying application environment to manipulation by malicious actors who craft specially formatted XML payloads containing dangerous entity definitions.
The technical mechanism of exploitation relies on the ability of an attacker to define a system identifier within an external entity that points to sensitive local resources. For instance, an attacker might construct an XML document that includes a reference to /etc/passwd or other configuration files stored on the target server's operating system. When the vulnerable version of XML::Atom processes this input without disabling external entities, it resolves these references and may include their contents within the parsed data structure returned to the application logic. Depending on how the host application handles the resulting data object, this information can be reflected back to the attacker through error messages, verbose logging outputs, or direct response bodies. This capability effectively bypasses standard access controls because the parsing engine operates with the same privileges as the user account running the Perl script, granting read access to files that would otherwise remain protected from external network requests.
The operational impact of this vulnerability is significant, primarily characterized by unauthorized data disclosure and potential information leakage regarding the internal infrastructure of the targeted system. Attackers can use this flaw to enumerate file paths, extract sensitive configuration details such as database credentials or API keys stored in local files, and gather intelligence that facilitates further attacks. In scenarios where the application logic processes the parsed XML content in a way that reflects output back to the user, the vulnerability becomes directly exploitable for remote data exfiltration. Even if direct reflection is not present, the ability to trigger server-side requests via blind XXE techniques can lead to Server-Side Request Forgery outcomes, allowing attackers to probe internal networks or interact with backend services that are not exposed to the public internet. This compromises the confidentiality and integrity of the application's data assets and undermines trust in the security posture of the deployed service.
From a classification perspective, this vulnerability aligns closely with CWE-611, which describes Improper Restriction of XML External Entity Reference. It also maps to specific techniques within the MITRE ATT&CK framework, particularly T1059.007 for Command and Scripting Interpreter if script execution is involved through entity resolution, or more commonly T1552.004 for Unsecured Credentials when used to extract sensitive files containing authentication data. The root cause lies in a default configuration that prioritizes XML feature completeness over security defaults, failing to adhere to the principle of least privilege by allowing potentially dangerous parsing behaviors without explicit opt-in requirements from the developer.
Mitigation strategies must focus on both immediate patching and long-term defensive coding practices. The primary remediation is to upgrade the XML::Atom module to version 0.39 or later, where this specific flaw has been addressed by enforcing stricter defaults regarding entity processing. For applications that cannot immediately update dependencies due to compatibility constraints, developers should implement input validation routines that sanitize incoming XML data before it reaches the parser. Furthermore, application-level configurations for any XML parsing library in use should explicitly disable DTDs and external entities if they are not strictly required for business logic. This involves setting appropriate flags or using secure configuration profiles provided by modern XML processing libraries to ensure that only well-formed, non-malicious content is processed. Regular security audits of dependency chains and the adoption of static application security testing tools can help identify similar vulnerabilities in other components before they reach production environments.