Which versions of Midscene Bridge Server are affected by CVE-2026-59804?

Midscene Bridge Server (versions through 1.10.3) contains a cross-origin WebSocket vulnerability allowing remote attackers to seize browser-automation sessions, intercept command data, and disable…. A patch is available.

Is there a public PoC exploit available for CVE-2026-59804?

Yes, a public proof-of-concept exploit is available for CVE-2026-59804. Prioritise patching immediately. EPSS: 0.2%.

How to fix or mitigate CVE-2026-59804?

Within 24 hours: Identify all systems running Midscene Bridge Server version 1.10.3 or earlier. Within 7 days: Apply vendor patch to all identified instances; if patch deployment is delayed, isolate Bridge Server instances to localhost-only access to prevent cross-origin attacks. Within 30 days: Complete audit of automation workflows executed during vulnerable window to detect potential payload injection or data exfiltration.

Midscene Bridge Server CVE-2026-59804

Q: What is the CVSS score of CVE-2026-59804?

CVE-2026-59804 has a CVSS 4.0 base score of 7.6 (High). CVSS vector: CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/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. EPSS exploitation probability: 0.2%.

EUVD-2026-42373 HIGH

Missing Origin Validation in WebSockets (CWE-1385)

2026-07-08 VulnCheck

GHSA-8rcx-4rjr-4wpf

Authentication Bypass Midscene

7.6

CVSS 4.0 · Vendor: VulnCheck

Severity by source

Vendor (VulnCheck) PRIMARY

7.6 HIGH

CVSS:4.0/AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:N/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

vuln.today AI

7.5 HIGH

Reachable via victim's browser (AV:N) but needs an active session and slot race (AC:H) plus victim visiting a malicious page (UI:R); no auth token (PR:N); command injection/exfiltration gives C:H/I:H and the unconditional kill gives A:H.

3.1 AV:N/AC:H/PR:N/UI:R/S:U/C:H/I:H/A:H

4.0 AV:N/AC:H/AT:N/PR:N/UI:P/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Primary rating from Vendor (VulnCheck).

CVSS VectorVendor: VulnCheck

Attack Vector

Network

Attack Complexity

High

Privileges Required

None

User Interaction

Scope

Lifecycle Timeline

Analysis Generated

Jul 08, 2026 - 20:32 vuln.today

DescriptionCVE.org

Midscene Bridge Server through 1.10.3, fixed in commit 86f4118, contains a missing authentication and CORS misconfiguration vulnerability that allows unauthenticated remote attackers to hijack active bridge sessions by opening a cross-origin WebSocket connection to the local Socket.IO server, which performs no Origin header validation and requires no authentication token. Attackers can connect from any web page visited by the victim to seize the single-client slot, intercept and inject automation commands, exfiltrate command-payload data, or unconditionally terminate the server by supplying the MIDSCENE_BRIDGE_SIGNAL_KILL query parameter.

AnalysisAI

Cross-origin WebSocket session hijacking in Midscene Bridge Server through version 1.10.3 lets any web page a victim visits connect to the locally running Socket.IO server without an Origin check or authentication token, seizing the tool's single-client slot. Once connected, a remote attacker can intercept and inject browser-automation commands, exfiltrate command-payload data, or unconditionally kill the server via the MIDSCENE_BRIDGE_SIGNAL_KILL query parameter. Publicly available exploit code exists (reported by VulnCheck) and a vendor patch is available (commit 86f4118); no active exploitation has been confirmed.

Technical ContextAI

Midscene is an AI-driven browser/UI automation framework from web-infra-dev; its Bridge Server exposes a local Socket.IO (WebSocket) endpoint that bridges automation commands between a client and the controlled browser session. The root cause is CWE-1385 (missing origin validation / omission of a security-relevant check during WebSocket handshake): the Socket.IO server performs no Origin header validation and requires no authentication token, so the browser's same-origin policy does not protect it - any origin can complete the WebSocket upgrade. Because the listener binds locally but is reachable from JavaScript running in any browser tab (WebSocket connections are not subject to CORS preflight for the connection itself), a malicious page loaded by the victim can silently open a connection to the localhost bridge port. The affected product is identified by CPE cpe:2.3:a:web-infra-dev:midscene.

RemediationAI

Upgrade to a Midscene release containing the fix in commit 86f4118 (https://github.com/web-infra-dev/midscene/commit/86f4118d1d847041c63d79e347e08c87c3f1a882), which adds Origin validation and authentication to the Bridge Server; an upstream fix is available via PR 2759 (https://github.com/web-infra-dev/midscene/pull/2759) but a specific tagged patched release version was not provided in the input, so confirm the exact release with the vendor advisory. Until upgraded, only start the Bridge Server when actively needed and stop it immediately afterward to shrink the exposure window (trade-off: manual overhead and interrupted long-running automation); avoid browsing untrusted sites in the same browser profile while a bridge session is live; and if your environment supports it, bind or firewall the Socket.IO listener so it is unreachable from browser-originated connections (trade-off: may break legitimate local clients that rely on the same interface). Refer to the VulnCheck advisory at https://www.vulncheck.com/advisories/midscene-bridge-server-session-hijack-via-unauthenticated-websocket for authoritative guidance.