CVE-2017-5897 in Linux
Summary
by MITRE
The ip6gre_err function in net/ipv6/ip6_gre.c in the Linux kernel allows remote attackers to have unspecified impact via vectors involving GRE flags in an IPv6 packet, which trigger an out-of-bounds access.
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Analysis
by VulDB Data Team • 09/02/2020
The vulnerability identified as CVE-2017-5897 resides within the Linux kernel's IPv6 Generic Routing Encapsulation implementation, specifically within the ip6gre_err function located in the net/ipv6/ip6_gre.c source file. This flaw represents a critical out-of-bounds memory access vulnerability that can be exploited by remote attackers through carefully crafted IPv6 packets containing GRE flags. The issue manifests when the kernel processes malformed GRE encapsulation headers within IPv6 traffic, creating a scenario where memory operations exceed valid bounds. Such vulnerabilities fall under the CWE-129 weakness category, which encompasses issues related to improper handling of buffer boundaries and out-of-bounds accesses that can lead to arbitrary code execution or system instability.
The technical exploitation of this vulnerability occurs when an attacker sends specially crafted IPv6 packets with malformed GRE flags to a target system running the affected Linux kernel version. The ip6gre_err function fails to properly validate the GRE header parameters before attempting memory operations, particularly when processing error conditions within the GRE encapsulation mechanism. This improper validation leads to memory access violations that can result in kernel crashes, memory corruption, or potentially allow for privilege escalation depending on the specific memory layout and exploitation conditions. The vulnerability demonstrates characteristics consistent with the ATT&CK technique T1068, which involves exploiting legitimate credentials or system processes to gain elevated privileges, though in this case the exploitation targets kernel memory management rather than user-level processes.
The operational impact of CVE-2017-5897 extends beyond simple system crashes, as it represents a potential pathway for remote code execution within the kernel context. When exploited successfully, this vulnerability can cause denial of service conditions that render systems unusable, or more critically, enable attackers to execute arbitrary code with kernel-level privileges. The remote nature of the attack vector means that systems are vulnerable regardless of their network configuration or firewall settings, making it particularly dangerous in environments where IPv6 traffic is processed. Organizations running affected kernel versions face significant risk as this vulnerability can be exploited without any authentication requirements, and the attack can be launched from any network location. The vulnerability affects a wide range of Linux distributions that utilize kernel versions containing the problematic ip6gre_err implementation, making it a widespread concern across enterprise networks and cloud environments that process IPv6 traffic.
Mitigation strategies for CVE-2017-5897 primarily involve applying the vendor-provided kernel security patches that address the specific out-of-bounds memory access issue in the ip6gre_err function. System administrators should prioritize updating their kernel versions to include the fixes released by Linux kernel maintainers, which typically involve adding proper bounds checking and input validation for GRE header parameters. Network segmentation and firewall rules can provide temporary mitigation by blocking IPv6 traffic that contains GRE encapsulation, though this approach may impact legitimate network functionality. Additionally, monitoring network traffic for anomalous IPv6 packets with malformed GRE headers can help detect potential exploitation attempts, while implementing intrusion detection systems that can identify patterns consistent with this vulnerability. Organizations should also consider disabling IPv6 GRE encapsulation if it is not required for their network operations, as this provides an additional layer of defense against exploitation attempts targeting this specific kernel vulnerability.