CVE-2016-5696 in Android
Summary
by MITRE
net/ipv4/tcp_input.c in the Linux kernel before 4.7 does not properly determine the rate of challenge ACK segments, which makes it easier for remote attackers to hijack TCP sessions via a blind in-window attack.
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Analysis
by VulDB Data Team • 09/22/2022
The vulnerability identified as CVE-2016-5696 resides in the Linux kernel's TCP implementation within the net/ipv4/tcp_input.c file and affects versions prior to 4.7. This flaw represents a significant security weakness in the kernel's handling of TCP acknowledgment segments, specifically concerning the rate calculation mechanism that governs challenge ACK generation. The issue enables attackers to manipulate TCP session hijacking attempts by exploiting the improper rate determination algorithm, making such attacks more feasible than would otherwise be possible.
The technical flaw stems from how the Linux kernel calculates the frequency at which challenge ACK segments are sent during TCP connection establishment and maintenance. Challenge ACKs serve as a security mechanism to verify that the communicating parties are still active and that the connection has not been compromised by an attacker who might be attempting to inject malicious packets or take control of the session. The kernel's implementation fails to correctly assess the appropriate rate for these challenge segments, creating a predictable pattern that attackers can exploit. This vulnerability specifically impacts the in-window attack vector where adversaries attempt to hijack established TCP connections without being detected.
The operational impact of this vulnerability is substantial as it allows remote attackers to perform blind TCP session hijacking attacks with increased success rates. An attacker positioned in the network path between communicating parties can leverage this weakness to inject packets into an existing TCP connection without prior knowledge of the sequence numbers, effectively taking control of the session. This capability undermines the fundamental security assumptions of TCP connections and can lead to complete compromise of network communications, data interception, and potential system infiltration. The vulnerability particularly affects environments where TCP connections are established across untrusted networks or where network monitoring is insufficient to detect such attacks.
The flaw aligns with CWE-200, which addresses information exposure, and relates to the broader category of network protocol vulnerabilities that compromise connection integrity. From an ATT&CK framework perspective, this vulnerability maps to techniques involving network sniffing, man-in-the-middle attacks, and session hijacking, specifically targeting the T1046 and T1557 sub-techniques related to network service scanning and credential access through network traffic interception. Organizations using affected Linux kernel versions face significant risk as this vulnerability can be exploited without requiring authentication or privileged access, making it particularly dangerous in environments with high network traffic volumes.
Mitigation strategies include upgrading to Linux kernel version 4.7 or later where the vulnerability has been addressed through improved rate calculation algorithms for challenge ACK segments. System administrators should also implement network monitoring solutions capable of detecting anomalous TCP behavior patterns and consider deploying additional security controls such as TCP sequence number randomization, connection tracking mechanisms, and network segmentation to reduce the attack surface. Organizations should conduct comprehensive vulnerability assessments to identify systems running affected kernel versions and prioritize patch deployment across their infrastructure. The vulnerability demonstrates the critical importance of maintaining up-to-date kernel versions and implementing robust network security monitoring to prevent exploitation of fundamental protocol weaknesses that can compromise entire network communications infrastructure.