CVE-2026-44635: Kysely: JSON-path traversal injection via unsanitized path-leg metacharacters in `JSONPathBuilder.key()` / `.at()`

Kysely 0.28.12 added a sanitizeStringLiteral() call inside DefaultQueryCompiler.visitJSONPathLeg (commit 0a602bf, PR #1727) to fix CVE-2026-32763 (GHSA-wmrf-hv6w-mr66). The fix only doubles single quotes (' → ''); it does not escape JSON-path metacharacters (., [, ], *, **, ?). When attacker-controlled input flows into eb.ref(col, '->$').key(input) or .at(input) — including type-safe code where the JSON column is shaped like Record<string, T> so K extends string is the inferred type — every dot becomes a path-leg separator, letting an attacker traverse from the intended key into sibling and child fields the developer never meant to expose. The result is read access (and, in update statements, write access) to JSON sub-fields outside the intended scope across MySQL, PostgreSQL ->$/->>$, and SQLite.

• Project: Kysely — TypeScript SQL query builder (npm kysely); affects MySQL, PostgreSQL ->$/->>$, and SQLite dialects.
• Source reviewed: kysely-org/kysely @ master (73192e4, version 0.28.16).
• Deployed artefact validated: kysely@0.28.16 from npm.
• Affected file(s):
• src/query-compiler/default-query-compiler.ts (lines 1611–1639, 1821–1823)
• src/query-builder/json-path-builder.ts (lines 93–196)
• src/dialect/mysql/mysql-query-compiler.ts (overrides sanitizeStringLiteral but inherits the same behaviour for path legs — escapes \ and ', nothing else)
• CWE: CWE-89 — Improper Neutralization of Special Elements used in an SQL Command, with CWE-915 / CWE-1284 (improper validation of specified quantity in input) flavours for the JSON-path sub-language.
• OWASP 2021: A03:2021 — Injection.