# CVE-2026-49859: Deno: `fetch()` API sandbox bypass via missing DNS resolution check

> An attacker can bypass network restrictions in Deno by using a domain that resolves to a blocked IP, circumventing the fetch() API's hostname checks.

- **Severity:** Medium 5.2 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 23 Jun 2026
- **Updated:** 24 Jun 2026
- **Also known as:** GHSA-cpgj-f7g3-2pp2, JLSEC-2026-1164

## What is CVE-2026-49859?

CVE-2026-49859 is a medium-severity server-side request forgery vulnerability in denoland deno, published on 23 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Deno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.8.1, when fetch() was called, 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. This vulnerability is fixed in 2.8.1.

Weakness: CWE-918 (Server-Side Request Forgery), CWE-693 (Protection Mechanism Failure)

## Which versions are affected by CVE-2026-49859?

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


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `deno` | crates.io | All versions | 2.8.1 |
| `deno` | crates.io | All versions | 2.8.1 |

Products: Deno Deno.

## How do I fix CVE-2026-49859?

Upgrade deno to 2.8.1 or later.

## Is CVE-2026-49859 being exploited?

There is no known exploitation of CVE-2026-49859 in the wild and no public exploit code.

## Other vulnerabilities in denoland deno

- [CVE-2023-28445](https://insights.sbomify.com/CVE-2023-28445/): Deno improperly handles resizable ArrayBuffer (critical 10.0)
- [CVE-2022-24783](https://insights.sbomify.com/CVE-2022-24783/): Sandbox bypass leading to arbitrary code execution in Deno (critical 10.0)
- [CVE-2021-32619](https://insights.sbomify.com/CVE-2021-32619/): Static imports inside dynamically imported modules do not adhere to permission checks (critical 9.8)
- [CVE-2026-22863](https://insights.sbomify.com/CVE-2026-22863/): Deno node:crypto doesn't finalize cipher (critical 9.2)
- [CVE-2024-27936](https://insights.sbomify.com/CVE-2024-27936/): Deno interactive permission prompt spoofing via improper ANSI stripping (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-49859 and fix it if it is affected.

What it is: CVE-2026-49859 is a medium-severity server-side request forgery vulnerability in denoland deno, published on 23 Jun 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-49859 in the wild and no public exploit code.

Affected packages and fixed versions:
- deno (crates.io): affected all versions; fixed in 2.8.1
- deno (crates.io): affected all versions; fixed in 2.8.1

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-49859/ (Markdown: https://insights.sbomify.com/CVE-2026-49859/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-49859
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-49859
- OSV: https://osv.dev/vulnerability/CVE-2026-49859

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-49859/
Summaries are generated and may contain mistakes; the official description above is the record.