Horizon Alert
Summary of the vulnerability and why it matters
A flaw in the Linux kernel's NFSv4.0 server can allow attackers to corrupt memory by exploiting how it handles lock requests. This memory corruption could potentially lead to system instability or unauthorized access.
- Remote exploitation possible.
- Can impact system stability.
- Requires specific client interaction.
Attack Path
How an attacker could exploit the issue
An attacker could exploit this flaw by tricking two cooperating NFSv4.0 clients into triggering a heap overflow in the NFS server. One client would set a lock with a large owner string, then the second client would request a conflicting lock. This denial would cause the server to attempt to write an oversized response into a fixed-size buffer, corrupting adjacent heap memory and potentially leading to remote code execution.
- Requires two clients.
- Targets NFSv4.0 server.
- Exploits LOCK operation denial.
Live Threat
Current exploitation, exposure, and threat context
This NFSv4.0 heap overflow can be triggered remotely by unauthenticated attackers using two cooperating clients. The vulnerability lies in the replay cache's fixed-size buffer being insufficient for certain LOCK denied responses, allowing up to 944 bytes of heap corruption.
- Exploitation requires two clients.
- No public exploit available.
- Fixes merged and backported.
Priority actions
Operational Fix
Recommended remediation, mitigation, and detection steps
Prioritize monitoring NFSv4.0 traffic for unusual LOCK operations and investigate systems running affected Linux kernel versions. If exploitation is detected or suspected, isolate affected NFS services immediately.
- Apply Linux kernel patch.
- Restrict NFSv4.0 network access.
- Monitor NFS logs for errors.
