t.String({ format: 'url' }) is vulnerable to redos
Repeating a partial url format (protocol and hostname) multiple times cause regex to slow down significantly
'http://a'.repeat(n)
Here's a table demonstrating how long it takes to process repeated partial url format
| n repeat | elapsed_ms |
| --- | --- |
| 1024 | 33.993 |
| 2048 | 134.357 |
| 4096 | 537.608 |
| 8192 | 2155.842 |
| 16384 | 8618.457 |
| 32768 | 34604.139 |
Patched by 1.4.26, please kindly update elysia to >= 1.4.26
Here's how long it takes after the patch
| n repeat | elapsed_ms |
| --- | --- |
| 1024 | 0.194 |
| 2048 | 0.274 |
| 4096 | 0.455 |
| 8192 | 0.831 |
| 16384 | 1.632 |
| 32768 | 3.052 |
It's recommended to always limit URL format to a reasonable length
t.String({
format: 'url',
maxLength: 288
})
If a long URL format is necessary, to patch this without updating to 1.4.26, add the following code to any part of your codebase
import { FormatRegistry } from '@sinclair/typebox'
FormatRegistry.Delete('url')
FormatRegistry.Set('url', (value) =>
/^(?:https?|ftp):\/\/(?:[^\s:@]+(?::[^\s@]*)?@)?(?:(?!(?:10|127)(?:\.\d{1,3}){3})(?!(?:169\.254|192\.168)(?:\.\d{1,3}){2})(?!172\.(?:1[6-9]|2\d|3[0-1])(?:\.\d{1,3}){2})(?:[1-9]\d?|1\d\d|2[01]\d|22[0-3])(?:\.(?:1?\d{1,2}|2[0-4]\d|25[0-5])){2}(?:\.(?:[1-9]\d?|1\d\d|2[0-4]\d|25[0-4]))|(?:(?:[a-z0-9\u{00a1}-\u{ffff}]+-)*[a-z0-9\u{00a1}-\u{ffff}]+)(?:\.(?:[a-z0-9\u{00a1}-\u{ffff}]+-)*[a-z0-9\u{00a1}-\u{ffff}]+)*(?:\.(?:[a-z\u{00a1}-\u{ffff}]{2,})))(?::\d{2,5})?(?:\/[^\s]*)?$/iu.test(
value
)
)
{
"severity": "HIGH",
"cwe_ids": [
"CWE-1333"
],
"github_reviewed": true,
"github_reviewed_at": "2026-03-10T21:04:25Z",
"nvd_published_at": "2026-03-10T21:16:47Z"
}