Jan Local API Server CORS Origin Reflection via 0.0.0.0 Binding

published 2026-07-24 3 mo ago modified 2026-10-24 15 d ago also EUVD-2026-48611

cvss: 6.3; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.3%; EPSS 0.3% chance of exploitation in 30 days, percentile 26%
public exploits: 0; none known

Jan through 0.8.4, fixed in commit 3e1c1e7, contains a CORS misconfiguration vulnerability in its local API server that allows network-adjacent attackers to bypass trusted host restrictions by exploiting the server's replacement of user-configured trusted hosts with a wildcard that reflects arbitrary origins with credentials. Attackers on the local network or using DNS rebinding can reach the unauthenticated OpenAI-compatible API to perform inference, enumerate models, invoke MCP tools, and read cross-origin responses.

Patch / fix

links 2

github.com/janhq/jan@3e1c1e7 commit
github.com/janhq/jan#8506 pull request

CISA SSVC

Exploitation: Proof of concept is public
Automatable: no
Technical impact: partial
Assessed: 3 mo ago (2026-07-24)

Exploit prediction

0.33% chance of exploitation in the next 30 days, higher than 26% of all scored CVEs (FIRST EPSS, 2026-11-08).

Exploits and checks

github.com https://github.com/janhq/jan/issues/8453 referenced PoC, tagged "exploit" by a source, unverified

CVSS scores

assigned by	version	score	vector
CNA	4.0	5.3	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N
CNA	3.1	6.3	CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L
CNA	4.0	5.3	CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:L/VI:L/VA:L/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

janhq jan

Classification

Weakness

CWE-183 Permissive List of Allowed Inputs
CWE-942 Permissive Cross-domain Security Policy with Untrusted Domains

References

github.com /janhq/jan/pull/8506
issue-tracking, patch
github.com /janhq/jan/commit/3e1c1e724f696620d89bb4a9cc18a380e0753757
patch
github.com /janhq/jan/issues/8453
technical-description, exploit, issue-tracking
vulncheck.com /advisories/jan-local-api-server-cors-origin-reflection-via-binding
third-party-advisory

Sources

CVE List CVE-2026-66005
NVD CVE-2026-66005

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary