CVE-2023-26103 Regular Expression Denial of Service in Deno.upgradeWebSocket API

What is CVE-2023-26103?

CVE-2023-26103 is a medium-severity denial of service vulnerability in deno, published on 25 Feb 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

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.

Weakness: CWE-1333

Which versions are affected by CVE-2023-26103?

2 open source packages ship an affected version, including deno. It affects 1 product.

Products include Deno Deno.

How do I fix CVE-2023-26103?

Upgrade deno to 1.31.0 or later.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2023-26103 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2023-26103 exists.

Other vulnerabilities in deno

• CVE-2023-28445 Deno improperly handles resizable ArrayBuffer Critical 10.0
• CVE-2022-24783 Sandbox bypass leading to arbitrary code execution in Deno Critical 10.0
• CVE-2021-32619 Static imports inside dynamically imported modules do not adhere to permission checks Critical 9.8
• CVE-2026-22863 Deno node:crypto doesn't finalize cipher Critical 9.2
• CVE-2024-27936 Deno interactive permission prompt spoofing via improper ANSI stripping High 8.8

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-jc97-h3h9-7xh6, JLSEC-2026-101.