Elo: Code injection in Elo backends via unvalidated emission of programmatic AST fields

Elo is a purely functional expression language for no-code tools. Prior to 1.0.1, Elo's programmatic AST API accepts arbitrary values from JSON-deserialized input, plugin output, or other untyped sources and interpolates them into generated JavaScript, Ruby, Python, or SQL without runtime syntax validation. The affected fields are int_literal / float_literal .value, variable.name, member_access.property, object_literal keys, datapath segments, lambda.params[].name, and the SQL let binding name. Crafted values become executable expressions or identifiers, allowing arbitrary code execution in JavaScript, Ruby, and Python targets and SQL injection in the SQL target. This programmatic AST-object path is distinct from the plain-string constructor-chain sandbox escape. This issue is fixed in version 1.0.1.

Elo is a purely functional expression language for no-code tools. Prior to 1.0.1, Elo's programmatic AST API accepts arbitrary values from JSON-deserialized input, plugin output, or other untyped sources and interpolates them into generated JavaScript, Ruby, Python, or SQL without runtime syntax validation. The affected fields are int_literal / float_literal .value, variable.name, member_access.property, object_literal keys, datapath segments, lambda.params[].name, and the SQL let binding name. Crafted values become executable expressions or identifiers, allowing arbitrary code execution in JavaScript, Ruby, and Python targets and SQL injection in the SQL target. This programmatic AST-object path is distinct from the plain-string constructor-chain sandbox escape. This issue is fixed in version 1.0.1.

Elo is a purely functional expression language for no-code tools. Prior to 1.0.1, Elo's programmatic AST API accepts arbitrary values from JSON-deserialized input, plugin output, or other untyped sources and interpolates them into generated JavaScript, Ruby, Python, or SQL without runtime syntax validation. The affected fields are int_literal / float_literal .value, variable.name, member_access.property, object_literal keys, datapath segments, lambda.params[].name, and the SQL let binding name. Crafted values become executable expressions or identifiers, allowing arbitrary code execution in JavaScript, Ruby, and Python targets and SQL injection in the SQL target. This programmatic AST-object path is distinct from the plain-string constructor-chain sandbox escape. This issue is fixed in version 1.0.1.

### Summary Elo's programmatic AST API accepts arbitrary values in many node fields without runtime type or syntax validation. Each backend's emit stage interpolates those values straight into the generated source with no escape pass. An integrator that populates the AST from JSON-deserialised input, plugin output, or any other untyped source therefore exposes a code-injection primitive that flows through to the emitted JavaScript, Ruby, Python, or SQL. The same pattern was previously addressed in **0.9.7 (2026-01-27)**, which patched the date/datetime/duration literal emitters via `JSON.stringify()` after a report by **naoyashiga**. This advisory generalises that fix to the remaining AST surface — at least 23 emission sites across six node-field categories and four backends. ### Vulnerable sinks Each row is a category of sinks that share the same shape: TypeScript signature erased at runtime → AST-API consumer passes a crafted value → emit interpolates the value verbatim. | # | AST field | Affected backends | Resulting injection | |---|---|---|---| | 1 | `int_literal` / `float_literal` `.value` | JS, Ruby, Python, SQL | Arbitrary expression in the emitted numeric position (RCE on JS/Ruby/Python; SQL expression injection) | | 2 | `variable.name` | JS, Ruby, Python, SQL | Identifier-position injection; on SQL, raw SQL injection because undefined identifiers are intentionally emitted as column references | | 3 | `member_access.property` | JS, Ruby, Python, SQL | Property access escaped into expression (RCE) | | 4 | `object_literal` key | JS, Ruby, SQL | Computed-key / extra-property injection (RCE on JS/Ruby; SQL injection) | | 5 | `datapath` segment | JS, Ruby, Python, SQL | Ruby symbol-list injection allows backtick shell exec; SQL string-segment unquoted in single-quote context allows SQL injection | | 6 | `lambda.params[].name` | JS, Ruby, Python | Parameter-list structural injection (RCE) | | 7 | SQL `let` binding `name` | SQL | Identifier injection in `… AS <name>` clause | ### Proof of Concept End-to-end execution was verified at commit `749af7b` for representative cases per backend. Examples: **Numeric literal injection (all four backends).** Feeding the following AST through `compileToJavaScript` emits a live `console.log` on call: ```js { type: 'literal', value: "(console.log('PWN_INT_JS'),1)" } // emits: (function(_) { return (console.log('PWN_INT_JS'),1); })(null); ``` The same AST against Ruby with `"(system('touch /tmp/pwn_int_ruby'); 1)"` creates the file; Python with `"(print('PWN_INT_PY') or 1)"` prints the sentinel; SQL emits the raw string into the numeric position. **SQL `variable.name` injection:** ```js { type: 'variable', name: "1; DROP TABLE users; --" } // emits: 1; DROP TABLE users; -- ``` **Ruby `datapath` segment shell-exec:** ```js { type: 'datapath', segments: ["a, system(`touch /tmp/pwn_dp_ruby`)"] } // emits: [:a, system(`touch /tmp/pwn_dp_ruby`)] ``` All ten end-to-end cases are automated in the `ast-exec.js` / `ast-exec2.js` scripts attached to the original report; each `console.log` and sentinel file was observed. ### Independence from GHSA #2 This finding is independent of **GHSA #2** (the `.constructor.constructor` sandbox escape). That report covers payloads delivered as plain Elo *strings* through the parser; the present advisory covers payloads delivered as AST *objects* through the programmatic API. The two threat models do not overlap: GHSA #2's identifier regex `^[a-zA-Z_][a-zA-Z0-9_]*$` accepts `constructor` (and is the right behaviour for a parser), while the present advisory adds runtime validation at every backend emit site so that AST-API consumers cannot inject arbitrary text into emitted source.