CVE-2026-49860
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedDeno is a JavaScript, TypeScript, and WebAssembly runtime. Prior to 2.8.1, 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. This vulnerability is fixed in 2.8.1.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceIn Deno prior to 2.8.1, the WebSocket connection handler validates destination hostnames against --deny-net rules but fails to subsequently validate the resolved IP addresses. An attacker can bypass network restrictions by using a domain name that passes hostname validation but resolves to a blocked IP address.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 2.8.1CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Local
- Complexity
- Low
- Privileges
- Low
- User interaction
- None
- Scope
- Changed
- Confidentiality
- Low
- Integrity
- Low
- Availability
- None
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Check Deno versionRun `deno --version` and note the version number displayedAffected if The version is below 2.8.1 (for example, 2.8.0, 2.7.0, etc.)
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Identify WebSocket usage in codeSearch codebase for WebSocket client usage patterns such as `new WebSocket()` or Deno's `Deno.connectWebSocket()` API callsAffected if WebSocket connections are being made to remote servers in the codebase
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Check if --deny-net is configuredReview how Deno is launched (command line, scripts, Docker entrypoints) for --deny-net flag with any network restrictionsAffected if --deny-net is used to restrict outbound network connections
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Verify hostname-to-IP validation gapTest a WebSocket connection using a domain name that passes hostname allowlist but resolves to a blocked IP range (compare hostname against --deny-net rules vs actual resolved IP)Affected if A domain passes hostname validation but connects to an IP that would be blocked if specified directly
You are affected if running Deno version below 2.8.1 AND using WebSocket connections with --deny-net restrictions, where the destination domain passes hostname validation but resolves to a blocked IP address.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped2.8.1
Upgrade Deno to version 2.8.1 or later. Until then, avoid relying solely on --deny-net rules for security-critical network restrictions in WebSocket contexts.
Deno 2.8.1
- Check current Deno version by running `deno --version`
- Upgrade Deno to version 2.8.1 using the official installation method: `curl -fsSL https://deno.land/install.sh | sh -s v2.8.1` or via your package manager
- Verify the upgrade was successful by running `deno --version` and confirming it shows 2.8.1 or higher
- Test that WebSocket connections now properly resolve and validate IP addresses against --deny-net rules
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation4.0 h
- Testing4.0 h
- Review / QA2.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-49860 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-49860 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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