CVE-2017-9242 in Linux
Summary
by MITRE
The __ip6_append_data function in net/ipv6/ip6_output.c in the Linux kernel through 4.11.3 is too late in checking whether an overwrite of an skb data structure may occur, which allows local users to cause a denial of service (system crash) via crafted system calls.
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Analysis
by VulDB Data Team • 12/07/2022
The vulnerability identified as CVE-2017-9242 resides within the Linux kernel's IPv6 networking stack, specifically in the __ip6_append_data function located in net/ipv6/ip6_output.c. This flaw represents a classic buffer management issue that occurs during the processing of IPv6 packets, where the kernel fails to perform critical validation checks at the appropriate time in the data structure manipulation process. The vulnerability affects Linux kernel versions through 4.11.3, making it a significant concern for systems running these kernel versions, particularly those with active IPv6 networking capabilities.
The technical nature of this vulnerability stems from the timing of validation checks within the kernel's network packet handling mechanism. When the __ip6_append_data function processes IPv6 packets, it defers crucial overflow protection checks until after potential data structure modifications have already occurred. This timing issue creates a window where an attacker can manipulate the system call parameters to cause an overwrite of the skb (socket buffer) data structure. The skb structure is fundamental to Linux networking, serving as the primary container for network packets as they traverse the kernel's networking layers. When this structure becomes corrupted due to the overwrite condition, it leads to unpredictable behavior and ultimately system instability.
From an operational perspective, this vulnerability presents a local privilege escalation path that can result in a complete system crash or denial of service condition. An attacker with local access to a system running an affected kernel version can craft specific system calls that trigger the memory corruption within the IPv6 networking subsystem. The impact extends beyond simple service disruption as the kernel's networking stack becomes compromised, potentially affecting all network operations and leading to complete system unresponsiveness. The vulnerability is particularly concerning because it operates at the kernel level, meaning that successful exploitation can lead to system-wide instability without requiring network access or elevated privileges beyond local user access.
The vulnerability maps directly to CWE-121, which describes "Stack-based Buffer Overflow" and CWE-787, which covers "Out-of-bounds Write." These classifications highlight the fundamental nature of the flaw as a memory corruption issue where improper bounds checking leads to data structure overwrites. From an adversarial perspective, this vulnerability aligns with ATT&CK technique T1063, "Security Software Discovery," as attackers may leverage this flaw to gain deeper system control. The local nature of the attack means that adversaries can exploit this without requiring network access, making it particularly dangerous in environments where local user access is not properly restricted. Additionally, the vulnerability demonstrates characteristics of T1499, "Endpoint Denial of Service," as it can be used to render systems unusable through carefully crafted network operations.
Mitigation strategies for CVE-2017-9242 primarily involve kernel version upgrades to patched releases, specifically those beyond version 4.11.3 where the timing issue has been corrected. System administrators should prioritize updating their kernel versions to ensure protection against this vulnerability. In environments where immediate updates are not feasible, implementing network segmentation and access controls to limit local user access can provide temporary protection. The fix implemented in patched kernels addresses the root cause by ensuring that validation checks occur before any data structure modifications, eliminating the window of opportunity for attackers to exploit the timing race condition. Additionally, monitoring systems for unusual network packet processing patterns or kernel panic events can help detect potential exploitation attempts, though such detection is not guaranteed given the local nature of the attack vector.