CVE-2026-4747

Summary

A high-severity stack-based buffer overflow vulnerability (CVE-2026-4747) has been identified in the Linux kernel's RPCSEC_GSS signature validation routine. Malformed NFS/RPCSEC_GSS packets can overflow a stack buffer during signature verification (CWE-121).

Technical Details

The issue is classified under CWE-121 (Stack-based Buffer Overflow). The RPCSEC_GSS protocol provides security services for RPC-based protocols (primarily NFS). Each data packet includes a cryptographic signature that the kernel validates. The validation routine copies signature data into a fixed-size stack buffer using an operation that does not verify the input length.

When an attacker sends a packet with an oversized signature field, the copy operation writes beyond the buffer boundary, overwriting the stack frame.

Exploitation Context

• Vector: Remote / Network-based
• Authentication: Not required
• Complexity: Low
• Impact: High (Confidentiality, Integrity, and Availability)

NFS servers are widely deployed in enterprise environments. A kernel-level buffer overflow in the NFS authentication subsystem provides a direct path to full host compromise from the network.

Remediation

Linux administrators should immediately:

1. Apply the latest kernel patch that adds proper bounds checking to the RPCSEC_GSS signature validation routine.
2. Restrict NFS port access (typically 2049/tcp) to trusted client networks using firewall rules.
3. Enable kernel stack protections (stack canaries, KASLR) to increase exploitation difficulty.

Precogs AI Integration

The Precogs AI Binary Security Platform identifies stack-based buffer overflow conditions in compiled kernel modules by analyzing signature verification routines for unsafe memory operations, detecting missing bounds checks before memcpy, strcpy, and similar functions.

Vulnerability Code Signature

Attack Data Flow

Vulnerable Code Pattern

// ❌ VULNERABLE: Stack-based Buffer Overflow
void process_data(char *input) {
    char buffer[64];
    // Taint sink: copies without bounds checking
    strcpy(buffer, input);
}

Secure Code Pattern

// ✅ SECURE: Bounded copy
void process_data(char *input) {
    char buffer[64];
    // Sanitized boundary check
    strncpy(buffer, input, sizeof(buffer) - 1);
    buffer[sizeof(buffer) - 1] = '\0';
}

How Precogs Detects This

Precogs Binary SAST engine explicitly uncovers memory boundary violations and unsafe memory management functions in compiled binaries.\n