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🛡️ JLSEC-2026-1165 — deno-jll (CVE-2026-49860)

⚪ Unknown ✅ No Known Exploit OSV
N/A
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Deno: WebSocket API sandbox bypass via missing post-DNS check

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-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.

How this vulnerability can be exploited

This issue can be reached with local access to the system, attack complexity is low, an attacker needs low-level privileges on the target. No user interaction is required. The scope is changed, meaning a successful attack can affect components beyond the vulnerable one. Rated impact: confidentiality low, integrity low, availability none.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N

  • Attack vector: Local — a local account, shell or session on the host is needed.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: Low — an ordinary user account is enough.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Changed — a successful attack reaches components beyond the vulnerable one.
  • Confidentiality impact: Low — limited, and the attacker does not choose what is affected.
  • Integrity impact: Low — limited, and the attacker does not choose what is affected.
  • Availability impact: None.

Affected software

JLSEC-2026-1165 is recorded against 1 package.

  • deno-jll

Timeline and source

Published on 5 August 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

github.com (Web)
github.com (Web)
nvd.nist.gov (Web)

Other advisories for this package

deno-jll has other advisories on record. If you are patching this one, these are worth checking on the same host:

Details

Severity Unknown
CVSS Score N/A
CVSS Vector CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
CWE N/A
Public Exploit ✅ No
Source OSV
Published 2026-08-05
Updated 2026-08-20
Modified 2026-08-05
Fix URL N/A

Affected Packages

Software From version Fixed in
deno-jll — —

Similar Threats

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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