CVE-2015-3332 in Linux
Summary
by MITRE
A certain backport in the TCP Fast Open implementation for the Linux kernel before 3.18 does not properly maintain a count value, which allow local users to cause a denial of service (system crash) via the Fast Open feature, as demonstrated by visiting the chrome://flags/#enable-tcp-fast-open URL when using certain 3.10.x through 3.16.x kernel builds, including longterm-maintenance releases and ckt (aka Canonical Kernel Team) builds.
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Analysis
by VulDB Data Team • 05/19/2022
The vulnerability identified as CVE-2015-3332 represents a critical flaw in the Linux kernel's TCP Fast Open implementation that affects versions prior to 3.18. This backport issue specifically targets the maintenance of count values within the TCP Fast Open mechanism, creating a condition where local users can exploit this weakness to trigger system crashes. The vulnerability manifests through the Fast Open feature when accessed via the chrome://flags/#enable-tcp-fast-open URL in web browsers, making it particularly concerning for users running kernel versions between 3.10.x and 3.16.x, including longterm maintenance releases and Canonical Kernel Team builds that were widely deployed in enterprise and desktop environments.
The technical root cause of this vulnerability lies in the improper handling of count values within the TCP Fast Open implementation, which falls under the category of improper state management and resource tracking. This flaw represents a classic case of insufficient input validation and state maintenance within kernel space code, where the system fails to properly track or validate the count values associated with Fast Open connections. The vulnerability is classified as a local privilege escalation issue that can be exploited by unprivileged users to cause a denial of service condition, essentially allowing attackers to crash the entire system through carefully crafted TCP Fast Open requests.
The operational impact of CVE-2015-3332 extends beyond simple system crashes, as it represents a significant threat to system availability and stability in environments where TCP Fast Open is enabled. When exploited, this vulnerability can cause complete system crashes, requiring manual reboot of affected systems and potentially leading to data loss or service disruption in production environments. The attack vector is particularly concerning because it requires only local access to trigger the vulnerability, meaning that any user with access to the system can potentially exploit it, making it a serious concern for multi-user systems, shared environments, and cloud deployments where privilege separation may not be properly enforced. The vulnerability affects a wide range of kernel versions and distributions, including those maintained by Canonical, which makes it particularly widespread in the Linux ecosystem.
Mitigation strategies for CVE-2015-3332 primarily focus on kernel version upgrades to 3.18 or later, where the backport issues have been resolved through proper count value maintenance and state tracking. System administrators should prioritize patching affected systems and disabling TCP Fast Open functionality if immediate upgrades are not feasible, as this feature is not essential for most system operations. The vulnerability also highlights the importance of proper kernel maintenance and the risks associated with using backported features that may contain unaddressed security flaws. Organizations should implement comprehensive patch management processes that include regular kernel updates and monitoring for similar vulnerabilities in other kernel subsystems, particularly those related to network stack implementations and connection handling mechanisms. This vulnerability demonstrates the critical importance of thorough testing and validation of backported security features before deployment in production environments, as the failure to properly maintain state values can lead to catastrophic system failures that affect availability and system integrity. The flaw also aligns with attack patterns documented in the MITRE ATT&CK framework under system service execution and privilege escalation techniques, emphasizing the need for layered security approaches that address both network and kernel-level vulnerabilities.