Versions of the package deno before 1.31.0 are vulnerable to Regular Expression Denial of Service (ReDoS) due to the upgradeWebSocket function, which contains regexes in the form of /s*,s*/, used for splitting the Connection/Upgrade header. A specially crafted Connection/Upgrade header can be used to significantly slow down a web socket server.
{
"sources": [
{
"id": "CVE-2023-26103",
"url": "https://services.nvd.nist.gov/rest/json/cves/2.0?cveId=CVE-2023-26103",
"html_url": "https://nvd.nist.gov/vuln/detail/CVE-2023-26103",
"published": "2023-02-25T05:15:12.343Z",
"modified": "2026-06-17T05:42:41.007Z",
"imported": "2026-07-17T21:08:38.099Z",
"database_specific": {
"status": "Modified"
}
}
],
"license": "CC-BY-4.0"
}