CVE-2026-49860 — deno
MEDIUMCVE-2026-49860 is a medium-severity (CVSS 5.2) Server-Side Request Forgery (SSRF) vulnerability in deno. A fix is available for deno — see the affected versions and patch details below.
Deno: WebSocket API sandbox bypass via missing post-DNS check
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-49860.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
CVE-2026-49860 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.
Where this sits among everything scored
Of 397,508 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.
Real-World Exposure
denoReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects crates.io packages — download data is not available via public APIs for these ecosystems.
Description
Summary
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.
Impact
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()).
Who is affected
Users who:
- run untrusted or third-party code with
deno run, and - rely on
--deny-netto 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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🦀crates.io | deno | all versions | 2.8.1cargo update -p deno --precise 2.8.1 |
Affected Products
denodenoDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for deno, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update deno to 2.8.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-49860 is resolved across your whole dependency graph.
Workarounds
Restrict outbound requests from the affected component to an allowlist of hosts, block access to link-local and internal address ranges at the network layer, and require authentication on internal services so a forged request cannot reach them unauthenticated.
Frequently Asked Questions
Is CVE-2026-49860 in your dependencies?
Find it across crates.io, including transitive dependencies.