Horizon Alert
Summary of the vulnerability and why it matters
A vulnerability in the Linux kernel's NFS server component could allow unauthorized data access or modification. This issue stems from incorrect calculations when handling data buffer sizes, potentially leading to security risks. The primary concern is to confirm if this specific NFS functionality is in use and exposed.
- Incorrect data buffer calculations create security risks.
- Confirm if this NFS feature is actively used.
- Assess relevance and potential exposure to your environment.
Attack Path
How an attacker could exploit the issue
An attacker can exploit this vulnerability by sending specially crafted network requests to a system running a vulnerable Linux kernel. These requests target the NFS (Network File System) service, specifically the `nfsd4_ff_encode_layoutget` function. Errors in how the system calculates the size of data being sent over the network (XDR encoding) can be abused. This can lead to the kernel writing data outside of its intended memory space or leaking uninitialized kernel memory to the attacker, potentially resulting in code execution or information disclosure.
- Network access required, no authentication.
- Triggered by malformed NFS layoutget requests.
- Memory corruption and sensitive data leakage.
Live Threat
Current exploitation, exposure, and threat context
The Linux kernel's NFS server (nfsd) component has a vulnerability in how it calculates XDR buffer sizes for layoutget operations. When supported, this could lead to an out-of-bounds write or the leaking of uninitialized kernel memory to an NFS client. This occurs due to incorrect handling of XDR padding, varying lengths for user and group IDs, and mismatches in length calculations for various fields. The most severe outcome, an out-of-bounds write, can happen with short strings and odd-sized file handles, potentially overwriting up to 5 bytes past the allocated buffer.
- Kernel memory could be leaked to clients.
- Errors in XDR buffer size calculations.
- Client may receive stale or unexpected data.
Operational Fix
Recommended remediation, mitigation, and detection steps
This vulnerability in the Linux kernel's NFS daemon (nfsd) could allow an unauthenticated attacker to cause an out-of-bounds write or leak uninitialized kernel memory. Real-world ownership would likely fall to the infrastructure or platform teams managing the Linux servers, with potential involvement from network and security teams for exposure assessment. The first practical step is to identify all NFS servers, determine their exposure, confirm the accountable owner, and then plan remediation based on the identified risk.
- Ownership: Infrastructure/Platform teams manage NFS servers.
- Verify: NFS server exposure and business criticality.
- Action: Plan remediation with vendor coordination.
