CVE-2019-5481 in cURL
Summary
by MITRE
Double-free vulnerability in the FTP-kerberos code in cURL 7.52.0 to 7.65.3.
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Analysis
by VulDB Data Team • 05/20/2025
The CVE-2019-5481 vulnerability represents a critical double-free memory corruption issue discovered in the File Transfer Protocol kerberos authentication implementation within the cURL library versions ranging from 7.52.0 through 7.65.3. This vulnerability resides within the kerberos authentication code path that handles FTP connections requiring kerberos security mechanisms. The flaw manifests when cURL processes FTP requests that involve kerberos authentication, specifically during the cleanup phase of authentication structures. The double-free condition occurs when the same memory block is deallocated twice, leading to potential memory corruption that can be exploited by malicious actors. This vulnerability directly impacts the security posture of any system utilizing cURL for FTP operations with kerberos authentication, as it creates opportunities for arbitrary code execution or denial of service conditions.
The technical implementation of this vulnerability stems from improper memory management within the kerberos authentication module of cURL's FTP handling code. When processing FTP connections that require kerberos authentication, the library allocates memory structures to manage authentication state and credentials. During connection termination or authentication failure scenarios, the code incorrectly frees the same memory block multiple times without proper nullification or reference counting mechanisms. This memory management flaw creates a situation where freed memory can be reallocated and potentially manipulated by an attacker, leading to unpredictable behavior including potential code execution. The vulnerability specifically affects the kerberos authentication flow in FTP operations and is classified under the CWE-415 double-free vulnerability category, which represents a well-known and dangerous class of memory corruption flaws. The flaw exists in the interaction between the kerberos authentication library integration and cURL's internal memory management routines.
The operational impact of CVE-2019-5481 extends beyond simple denial of service scenarios to encompass potential remote code execution capabilities. Systems that utilize cURL for FTP operations with kerberos authentication are at risk of being compromised when exploited by attackers who can manipulate FTP connections to trigger the double-free condition. The vulnerability is particularly concerning in environments where cURL is used as a library component in larger applications, web servers, or automated systems that process untrusted FTP data. Attackers could potentially leverage this vulnerability to execute arbitrary code on vulnerable systems, leading to complete system compromise or data exfiltration. The attack vector requires an attacker to control or influence FTP connections that utilize kerberos authentication, making it somewhat more constrained than other memory corruption vulnerabilities but still highly impactful. This vulnerability aligns with ATT&CK technique T1059.007 for execution through command and scripting interpreter and T1105 for remote service access through FTP protocols.
Mitigation strategies for CVE-2019-5481 primarily focus on immediate version updates to cURL 7.65.4 or later, which contains the necessary patches to address the double-free condition. Organizations should conduct comprehensive vulnerability assessments to identify all systems utilizing affected cURL versions, particularly those handling FTP connections with kerberos authentication. System administrators should implement network segmentation to limit exposure of vulnerable systems to untrusted FTP traffic and consider disabling kerberos authentication for FTP connections where possible. The patch released by the cURL project addresses the memory management issue by ensuring proper reference counting and memory deallocation sequences during kerberos authentication cleanup. Additionally, organizations should monitor for any related vulnerabilities in their software supply chains that might be affected by similar memory management flaws. Regular security updates and patch management procedures should be enforced to prevent exploitation of similar vulnerabilities in other components of the software ecosystem. The fix implements proper memory management practices that prevent the double-free condition while maintaining the functionality of kerberos authentication for legitimate FTP operations.