CVE-2026-85730

smol-toml is a small, fast, and correct TOML parser and serializer. Prior to 1.7.1, parse() can enter an infinite loop when a value inside an array or inline table is followed by a comment with no trailing newline. In src/util.ts, skipUntil() calls indexOfNewline(), receives -1 at the end of input, and resets the cursor to the beginning of the string instead of leaving the structure scan. The parser then hangs indefinitely and can consume a service's processing capacity when an application parses attacker-controlled TOML. This issue is fixed in version 1.7.1.

smol-toml is a small, fast, and correct TOML parser and serializer. Prior to 1.7.1, parse() can enter an infinite loop when a value inside an array or inline table is followed by a comment with no trailing newline. In src/util.ts, skipUntil() calls indexOfNewline(), receives -1 at the end of input, and resets the cursor to the beginning of the string instead of leaving the structure scan. The parser then hangs indefinitely and can consume a service's processing capacity when an application parses attacker-controlled TOML. This issue is fixed in version 1.7.1.

Summary

parse() can be forced into an infinite loop when a value inside an array or inline table is followed by a comment that has no trailing newline (i.e. the comment "ends" the document).

The library fails to exit an internal loop when attempting to find the end of the structure, resetting its cursor to the beginning of the string instead. This causes the parser to indefinitely hang, compromising the availability of the service.

Proof of concept

import { parse } from 'smol-toml'
parse('a=[1 #')   // never returns; CPU pinned at 100%

Impact

Applications which parse arbitrary TOML documents can suffer major availability issues if they receive malicious input. This issue is particularly severe for these use-cases, and it is strongly advised to upgrade to an up-to-date version of the library as soon as possible.

If your use-case does not involve parsing arbitrary TOML documents from untrusted sources, the impact is much lower in practice, although it's still advisable to update to version 1.7.1.

Patches

Version 1.7.1 properly breaks out of the loop in these situations and throws the expected TomlError.

Workarounds

None that don't involve refactors. Update the library as soon as possible if your use-case involves parsing arbitrary TOML documents from untrusted sources.

Reported By : Ravindu Lakmina Munaweera

Summary

An attacker can send a maliciously crafted TOML to cause the parser to crash, because of a stack overflow caused by thousands of consecutive commented lines.

The library uses recursion internally while parsing to skip over commented lines, which can be exploited to crash an application that is processing arbitrary TOML documents.

Proof of concept

require("smol-toml").parse('# comment\n'.repeat(8000) + 'key = "value"')

Impact

Applications which parse arbitrary TOML documents may suffer availability issues if they receive malicious input. If uncaught, the crash may cause the application itself to crash. The impact is deemed minor, as the function is already likely to throw errors on invalid input. Downstream users are supposed to properly handle errors in such situations.

Due to the design of most JavaScript runtimes, the uncontrolled recursion does not lead to excessive memory usage and the execution is quickly aborted.

As a reminder, it is strongly advised when working with untrusted user input to expect errors to occur and to appropriately catch them.

Patches

Version 1.6.1 uses a different approach for parsing comments, which no longer involves recursion.

Workarounds

Wrap all invocations of parse and stringify in a try/catch block when dealing with untrusted user input.

smol-toml is a small, fast, and correct TOML parser and serializer. Prior to 1.7.1, parse() can enter an infinite loop when a value inside an array or inline table is followed by a comment with no trailing newline. In src/util.ts, skipUntil() calls indexOfNewline(), receives -1 at the end of input, and resets the cursor to the beginning of the string instead of leaving the structure scan. The parser then hangs indefinitely and can consume a service's processing capacity when an application parses attacker-controlled TOML. This issue is fixed in version 1.7.1.

smol-toml is a small, fast, and correct TOML parser and serializer. Prior to 1.7.1, parse() can enter an infinite loop when a value inside an array or inline table is followed by a comment with no trailing newline. In src/util.ts, skipUntil() calls indexOfNewline(), receives -1 at the end of input, and resets the cursor to the beginning of the string instead of leaving the structure scan. The parser then hangs indefinitely and can consume a service's processing capacity when an application parses attacker-controlled TOML. This issue is fixed in version 1.7.1.