# CVE-2026-49860: Deno sandbox bypass via missing post-DNS check in WebSocket API

Source: https://junglewise.ai/threats/cve-2026-49860-deno-sandbox-bypass-via-missing-post-dns-check-in-websocket-api  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-23. Updated: 2026-06-23  
License: CC BY 4.0 with a link back

CVE-2026-49860 · Severity: medium · CVSS 5.2 · Published 2026-06-23

Deno is a software runtime used to execute JavaScript and TypeScript applications. A security flaw in its WebSocket implementation allowed malicious or untrusted scripts to bypass network restrictions intended to block access to specific internal servers or sensitive local addresses. This could allow an attacker to communicate with restricted internal services, potentially leading to unauthorized data access or internal system interference.

Technologies: [deno (crates.io)](https://junglewise.ai/threats/technologies/deno). Vendors: [crates.io](https://junglewise.ai/threats/vendors/crates-io).

## Quick answers

**Is CVE-2026-49860 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-49860 being exploited in the wild.

**How severe is CVE-2026-49860?** Medium severity, with a CVSS score of 5.2, published 23 June 2026.

**Which products and versions are affected?** deno (crates.io) <= 2.8.0, SEMVER:introduced=0,fixed=2.8.1.

**Is there a fix for CVE-2026-49860?** Yes. deno (crates.io): upgrade to 2.8.1 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-49860 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-49860?** Check whether you run deno (crates.io) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- deno (crates.io): upgrade to 2.8.1 or later

  ```sh
  cargo update -p deno
  ```


## Technical details

A Server-Side Request Forgery (SSRF) vulnerability exists in Deno's WebSocket API due to a missing post-DNS resolution check. While Deno validates the initial hostname against the '--deny-net' blocklist, it fails to verify the resulting IP address after DNS resolution. An attacker can exploit this by using a DNS rebinding-style attack or a specially crafted domain that resolves to a restricted IP (such as 127.0.0.1 or internal metadata services). This allows a script running in the Deno sandbox to establish WebSocket connections to prohibited network destinations. The issue is specific to the WebSocket implementation and does not affect Deno.connect or fetch(). The vulnerability is resolved in version 2.8.1.

## Affected products

- denoland Deno < 2.8.1

## Identifiers

- CVE-2026-49860
- GHSA-83pc-3rw9-qpwj

## Timeline

- 2026-05-27: advisory: GitHub advisory published by maintainers
- 2026-06-23: disclosed: CVE published to NVD
- 2026-06-23: patched: Fix released in version 2.8.1

## References

- [https://github.com/denoland/deno/security/advisories/GHSA-83pc-3rw9-qpwj](https://github.com/denoland/deno/security/advisories/GHSA-83pc-3rw9-qpwj)

## Related threats

- [Deno denial of service via non-ASCII WebSocket response headers](https://junglewise.ai/threats/cve-2026-55517-deno-denial-of-service-via-non-ascii-websocket-response-headers)
- [Deno environment permission bypass in process.loadEnvFile](https://junglewise.ai/threats/cve-2026-49983-deno-environment-permission-bypass-in-process-loadenvfile)
- [Deno network restriction bypass in fetch API](https://junglewise.ai/threats/cve-2026-49859-deno-network-restriction-bypass-in-fetch-api)
- [Deno missing cryptographic rounds in node:crypto checkPrime](https://junglewise.ai/threats/cve-2026-49440-deno-missing-cryptographic-rounds-in-node-crypto-checkprime)
- [Deno network permission bypass via numeric hostname aliases in Node.js compatibility layer](https://junglewise.ai/threats/cve-2026-49411-deno-network-permission-bypass-via-numeric-hostname-aliases-in)