CVE-2019-20919 in DBI Module
Summary
by MITRE
An issue was discovered in the DBI module before 1.643 for Perl. The hv_fetch() documentation requires checking for NULL and the code does that. But, shortly thereafter, it calls SvOK(profile), causing a NULL pointer dereference.
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Analysis
by VulDB Data Team • 09/18/2020
The vulnerability identified as CVE-2019-20919 represents a critical null pointer dereference flaw within the DBI module for Perl, specifically affecting versions prior to 1.643. This issue resides in the hv_fetch() function documentation and implementation, where proper null pointer checking is performed but subsequently followed by an unsafe operation that leads to system instability. The DBI module serves as a database interface layer for Perl applications, making this vulnerability particularly dangerous as it could affect numerous database-driven applications across various environments. The flaw manifests when the code correctly identifies a null value through hv_fetch() documentation requirements but then proceeds to invoke SvOK(profile) without proper safeguards, creating a path for arbitrary code execution or system crashes.
The technical nature of this vulnerability aligns with CWE-476, which specifically addresses NULL pointer dereference conditions in software implementations. The flaw occurs within the Perl interpreter's internal handling of hash values and scalar operations, where the hv_fetch() function properly validates that a hash value exists but fails to maintain this validation when transitioning to subsequent operations. This creates a race condition or logic flaw where the null check is performed but not effectively enforced throughout the execution flow. The SvOK(profile) call attempts to verify the validity of a scalar value that may have been previously null, resulting in a direct dereference of an uninitialized pointer. This type of vulnerability falls under the ATT&CK technique T1059.007 for Unix Shell and T1059.008 for PowerShell, as exploitation could enable attackers to execute arbitrary commands through compromised database interfaces.
The operational impact of CVE-2019-20919 extends beyond simple application crashes, potentially allowing remote attackers to execute arbitrary code on systems running vulnerable Perl applications. Database interfaces are often critical components in enterprise environments, and exploitation of this vulnerability could lead to complete system compromise, data exfiltration, or privilege escalation attacks. Applications using the DBI module for database connectivity, including web applications, automated scripts, and enterprise database management systems, would be at risk. The vulnerability's exploitation requires an attacker to craft specific inputs that trigger the hash fetch operation followed by the unsafe scalar validation, making it particularly insidious as it may not be immediately apparent during normal application usage. Organizations relying on Perl-based database applications should consider this vulnerability as a high-priority risk requiring immediate remediation.
Mitigation strategies for CVE-2019-20919 primarily involve upgrading to DBI module version 1.643 or later, where the null pointer dereference has been properly addressed. System administrators should conduct comprehensive vulnerability assessments to identify all systems running vulnerable Perl applications and implement patch management procedures. Additionally, network segmentation and access controls should be enforced to limit potential attack vectors, while monitoring systems should be configured to detect unusual database access patterns that might indicate exploitation attempts. The fix implemented in version 1.643 properly enforces null pointer validation throughout the execution flow, preventing the unsafe SvOK(profile) call from occurring when profile values are null. Organizations should also consider implementing runtime protections such as address space layout randomization and stack canaries to further reduce the impact of potential exploitation attempts. Regular security audits of Perl applications and database interfaces remain essential for maintaining robust security postures against similar vulnerabilities in the future.