CVE-2020-25211 in Linux
Summary
by MITRE
In the Linux kernel through 5.8.7, local attackers able to inject conntrack netlink configuration could overflow a local buffer, causing crashes or triggering use of incorrect protocol numbers in ctnetlink_parse_tuple_filter in net/netfilter/nf_conntrack_netlink.c, aka CID-1cc5ef91d2ff.
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Analysis
by VulDB Data Team • 09/09/2020
The vulnerability identified as CVE-2020-25211 represents a critical buffer overflow flaw within the Linux kernel's netfilter subsystem, specifically affecting versions through 5.8.7. This issue resides in the ctnetlink_parse_tuple_filter function located in net/netfilter/nf_conntrack_netlink.c, making it accessible to local attackers who can manipulate conntrack netlink configuration. The vulnerability stems from inadequate input validation when processing network connection tracking data, creating a scenario where maliciously crafted netlink messages can trigger memory corruption. The flaw is categorized under CWE-121 as a stack-based buffer overflow, which occurs when data is written beyond the bounds of a fixed-size buffer, potentially leading to system instability or arbitrary code execution.
The operational impact of this vulnerability extends beyond simple system crashes, as it can cause incorrect protocol number handling that affects the entire connection tracking mechanism. When attackers successfully exploit this buffer overflow, they can cause the kernel to process malformed netlink messages that result in memory corruption, leading to unpredictable behavior including system panics, denial of service conditions, and potential privilege escalation. The ctnetlink subsystem is responsible for managing connection tracking information through netlink sockets, making it a critical component for network packet filtering and stateful inspection. Attackers who can inject conntrack netlink configuration data can leverage this vulnerability to disrupt network services or potentially gain elevated privileges within the kernel space.
From an attack perspective, this vulnerability aligns with ATT&CK technique T1068 which involves exploiting legitimate credentials and system access to escalate privileges. The local nature of this attack means that exploitation requires an attacker to already have access to the system, but the potential for privilege escalation makes it particularly dangerous in environments where local users or processes might be compromised. The vulnerability is especially concerning in containerized environments or systems where multiple users share resources, as a compromised local user could potentially exploit this to affect other processes or even the host system itself. The buffer overflow in ctnetlink_parse_tuple_filter demonstrates a classic memory safety issue where insufficient bounds checking allows attackers to overwrite adjacent memory locations, potentially corrupting kernel data structures or executing arbitrary code.
Mitigation strategies for CVE-2020-25211 should focus on immediate kernel updates to versions 5.8.8 or later where the vulnerability has been patched through proper bounds checking and input validation. System administrators should also implement network segmentation and access controls to limit local user privileges, reducing the attack surface for potential exploitation. Additionally, monitoring for unusual conntrack netlink activity and implementing kernel hardening measures such as stack canaries and address space layout randomization can help detect or prevent exploitation attempts. The patch for this vulnerability specifically addresses the buffer overflow by implementing proper size validation when parsing tuple filters, ensuring that input data cannot exceed allocated buffer boundaries. Organizations should also consider implementing intrusion detection systems that can identify suspicious netlink message patterns and maintain regular security audits to ensure all systems are running patched kernel versions.