CVE-2013-4359 in ProFTPD
Summary
by MITRE
Integer overflow in kbdint.c in mod_sftp in ProFTPD 1.3.4d and 1.3.5r3 allows remote attackers to cause a denial of service (memory consumption) via a large response count value in an authentication request, which triggers a large memory allocation.
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Analysis
by VulDB Data Team • 05/24/2021
The vulnerability described in CVE-2013-4359 represents a critical integer overflow flaw within the ProFTPD mod_sftp module that affects versions 1.3.4d and 1.3.5r3. This issue resides in the kbdint.c file which handles keyboard interactive authentication mechanisms. The vulnerability manifests when the authentication process receives a malformed response count value that exceeds the maximum representable integer value, causing the system to allocate an unexpectedly large amount of memory. This flaw operates at the intersection of software implementation and memory management, where the integer overflow directly translates into resource exhaustion rather than traditional code execution exploits.
The technical implementation of this vulnerability stems from improper input validation within the keyboard interactive authentication flow. When a remote attacker submits an authentication request containing an excessively large response count value, the system fails to properly validate the integer bounds before proceeding with memory allocation operations. The mod_sftp module processes this malformed input without adequate boundary checking, leading to a scenario where the integer overflow causes the malloc function to attempt allocating memory in the range of several gigabytes or more. This type of vulnerability aligns with CWE-190, which specifically addresses integer overflow conditions that can lead to memory allocation failures and resource exhaustion attacks.
From an operational perspective, this vulnerability creates a significant denial of service condition that can be exploited by remote attackers without requiring authentication credentials. The memory consumption aspect of this flaw means that systems running affected versions of ProFTPD can be rendered completely unresponsive as the system consumes all available memory resources. The impact extends beyond simple service disruption to potentially affecting other services running on the same system due to the resource exhaustion. This vulnerability particularly affects environments where ProFTPD serves as a primary file transfer service and where authentication requests are frequently processed, making it a prime target for resource exhaustion attacks that can effectively shut down critical infrastructure.
The attack surface for this vulnerability encompasses any system running the affected ProFTPD versions with mod_sftp enabled and accepting keyboard interactive authentication requests. Security practitioners should consider this issue in the context of the ATT&CK framework's privilege escalation and denial of service tactics, as attackers can leverage this flaw to consume system resources and potentially disrupt legitimate user access. Mitigation strategies should include immediate patching of the affected ProFTPD versions to the latest stable releases that contain the integer overflow fixes. Organizations should also implement network segmentation and access controls to limit exposure to this vulnerability, while monitoring authentication logs for suspicious activity patterns that might indicate exploitation attempts. Additionally, implementing memory limits and resource monitoring on affected systems can help detect and respond to exploitation attempts before complete service disruption occurs.