CVE-2015-3636 in Linux
Summary
by MITRE
The ping_unhash function in net/ipv4/ping.c in the Linux kernel before 4.0.3 does not initialize a certain list data structure during an unhash operation, which allows local users to gain privileges or cause a denial of service (use-after-free and system crash) by leveraging the ability to make a SOCK_DGRAM socket system call for the IPPROTO_ICMP or IPPROTO_ICMPV6 protocol, and then making a connect system call after a disconnect.
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Analysis
by VulDB Data Team • 05/10/2022
The vulnerability described in CVE-2015-3636 represents a critical flaw in the Linux kernel's implementation of ICMP socket handling that enables local privilege escalation and system instability. This vulnerability resides within the ping_unhash function located in net/ipv4/ping.c, specifically affecting Linux kernel versions prior to 4.0.3. The flaw manifests when a local attacker creates a SOCK_DGRAM socket using IPPROTO_ICMP or IPPROTO_ICMPV6 protocols and subsequently performs connect and disconnect operations on this socket. The root cause stems from improper initialization of a list data structure during the unhash operation, creating a scenario where memory management becomes compromised and exploitable.
The technical exploitation of this vulnerability leverages the use-after-free condition that occurs when the kernel fails to properly initialize a list structure during socket cleanup operations. When a socket is disconnected and then reconnected, the ping_unhash function does not properly reset the list head, leaving it in an uninitialized state. This creates a situation where freed memory can be accessed and manipulated by subsequent operations, enabling attackers to execute arbitrary code with kernel privileges. The vulnerability specifically targets the kernel's socket management subsystem and demonstrates a classic memory corruption flaw that has been classified under CWE-415 as Double Free or CWE-416 as Use After Free. The attack requires only local user privileges and can be executed through standard socket system calls, making it particularly dangerous as it does not require special permissions or network access.
The operational impact of CVE-2015-3636 extends beyond simple privilege escalation to include potential system crashes and denial of service conditions that can render affected systems unstable. When exploited successfully, the vulnerability allows attackers to execute code with the highest possible privileges, effectively compromising the entire system and potentially enabling further attacks against network infrastructure or other connected systems. The use-after-free condition can be reliably triggered through standard socket operations, making this vulnerability particularly dangerous in environments where local users have access to system resources. This flaw aligns with ATT&CK technique T1068 which describes the exploitation of local privilege escalation vulnerabilities, and specifically demonstrates how kernel-level memory corruption can be leveraged for system compromise. The vulnerability's impact is amplified by the fact that it can be triggered through legitimate system calls, making detection and prevention challenging.
Mitigation strategies for CVE-2015-3636 focus primarily on kernel version updates and system hardening measures. The most effective remediation involves upgrading to Linux kernel version 4.0.3 or later, where the ping_unhash function has been properly patched to initialize all required list structures during unhash operations. System administrators should also implement monitoring for unusual socket activity patterns that might indicate exploitation attempts, particularly around ICMP socket operations. Additional security measures include restricting local user privileges where possible, implementing proper access controls for system resources, and conducting regular vulnerability assessments to identify similar memory corruption issues. The patch addresses the root cause by ensuring proper initialization of the list data structure, preventing the use-after-free condition that enables privilege escalation. Organizations should also consider implementing kernel module signing and integrity checking mechanisms to prevent exploitation of similar vulnerabilities in the future, as this represents a fundamental flaw in kernel memory management that could potentially affect other subsystems if similar initialization issues exist.