CVE-2026-49860

When a WebSocket connection was opened, Deno checked the destination hostname
against --deny-net rules but did not re-check the IP addresses that hostname
resolved to. An attacker-controlled script could use a specially crafted domain
name that passes the hostname check yet resolves to a denied IP, bypassing the
network restriction entirely.

Who is affected

Users who:

• run untrusted or third-party code with deno run, and
• rely on --deny-net to restrict which hosts that code can reach.

If you do not use --deny-net, or if you only run fully trusted code, you are
not affected.

Workaround

No workaround is available short of upgrading. If upgrading immediately is not
possible, avoid granting --allow-net to untrusted code that also has
--deny-net restrictions you depend on for security.

Code running under --deny-net could connect to hosts that the user intended
to block. In practice this means network isolation rules, for example,
blocking access to localhost or internal services, could be silently
circumvented by a malicious or compromised dependency.

Deno.connect and fetch() were not affected by this specific issue (a
companion advisory covers fetch()).

Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside. Typical impact: access to internal metadata services, internal APIs, or cloud credentials.

CVE-2026-49860 has a CVSS score of 5.2 (Medium). The vector is requires local access, low privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.8.1); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-49860? CVE-2026-49860 is a medium-severity server-side request forgery (SSRF) vulnerability in deno (rust), affecting versions <= 2.8.0. It is fixed in 2.8.1. Untrusted input controls the target URL of a server-initiated request, which may reach internal services not otherwise accessible from outside.
2. How severe is CVE-2026-49860? CVE-2026-49860 has a CVSS score of 5.2 (Medium). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which versions of deno are affected by CVE-2026-49860? deno (rust) versions <= 2.8.0 is affected.
4. Is there a fix for CVE-2026-49860? Yes. CVE-2026-49860 is fixed in 2.8.1. Upgrade to this version or later.
5. Is CVE-2026-49860 exploitable, and should I be worried? Whether CVE-2026-49860 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-49860 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-49860? Upgrade deno to 2.8.1 or later.