Cyber Resilience

CVE-2026-34403

Nginxui Nginx Ui ≤ 2.3.5

Public PoC
Published
20 April 2026
Modified
22 April 2026
Patch / advisory
View advisory
CVSS Score v4 5.5
Click a component to see what it means
Raw vectorCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:A/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N/E:P/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 Score 0.0018 7th percentile
Risk Priority 35 floored blend · peak EPSS

Summary

CVE-2026-34403 is a medium-severity Missing Origin Validation in WebSockets (CWE-1385) vulnerability in Nginxui Nginx Ui. Its CVSS base score is 5.5 (Medium).

Operationally, exploitation aligns with the MITRE ATT&CK technique Browser Session Hijacking (T1185); ranked at the 7th percentile by exploit likelihood (below the median); it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.

The strongest mitigations our analysis identified map to AC-3 (Access Enforcement) and AC-4 (Information Flow Enforcement) — see the control section below for these in your framework.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2026-34403 is a Cross-Site WebSocket Hijacking (CSWSH) vulnerability, tracked under CWE-1385, affecting Nginx UI, a web user interface for the Nginx web server. In versions prior to 2.3.5, all WebSocket endpoints utilize a gorilla/websocket Upgrader where the CheckOrigin function unconditionally returns true, bypassing origin validation. This issue is exacerbated by authentication tokens stored in browser cookies set via JavaScript, lacking HttpOnly or explicit SameSite attributes, enabling cross-site access to these tokens. The vulnerability carries a CVSS v3.1 base score of 8.1 (AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N).

An attacker can exploit this vulnerability by luring a logged-in administrator to visit an attacker-controlled webpage. The malicious page can then establish authenticated WebSocket connections to the nginx-ui instance, leveraging the victim's cookies for authentication. This allows the attacker to perform actions on behalf of the administrator over the hijacked WebSocket, potentially compromising confidentiality and integrity of the nginx-ui configuration and related Nginx server management.

The GitHub security advisory (GHSA-78mf-482w-62qj) and release notes for version 2.3.5 detail the patch, which addresses the CheckOrigin misconfiguration and cookie handling deficiencies. Security practitioners should upgrade to nginx-ui version 2.3.5 or later to mitigate the issue, and review WebSocket implementations for similar origin validation flaws.

EU & UK References

Vulnerability Data

Nginx UI is a web user interface for the Nginx web server. Prior to version 2.3.5, all WebSocket endpoints in nginx-ui use a gorilla/websocket Upgrader with CheckOrigin unconditionally returning true, allowing Cross-Site WebSocket Hijacking (CSWSH). Combined with the fact that…

more

authentication tokens are stored in browser cookies (set via JavaScript without HttpOnly or explicit SameSite attributes), a malicious webpage can establish authenticated WebSocket connections to the nginx-ui instance when a logged-in administrator visits the attacker-controlled page. Version 2.3.5 patches the issue.

CWE(s)
CWE-1385

Related Threats

MITRE ATT&CK Enterprise Techniques

T1185 Browser Session Hijacking Collection
Adversaries may take advantage of security vulnerabilities and inherent functionality in browser software to change content, modify user-behaviors, and intercept information as part of various browser session hijacking techniques.
attack.mitre.org →
T1190 Exploit Public-Facing Application Initial Access
Adversaries may attempt to exploit a weakness in an Internet-facing host or system to initially access a network.
attack.mitre.org →
T1557 Adversary-in-the-Middle Credential Access
Adversaries may attempt to position themselves between two or more networked devices using an adversary-in-the-middle (AiTM) technique to support follow-on behaviors such as [Network Sniffing](https://attack.
attack.mitre.org →
Derived from this CVE’s CWE(s) via the direct CWE→ATT&CK cross-walk.

CVEs Like This One

CVE-2026-44015Same product: Nginxui Nginx Ui
CVE-2024-23827Same product: Nginxui Nginx Ui
CVE-2024-22196Same product: Nginxui Nginx Ui
CVE-2024-49366Same product: Nginxui Nginx Ui
CVE-2026-42221Same product: Nginxui Nginx Ui
CVE-2026-33027Same product: Nginxui Nginx Ui
CVE-2026-27944Same product: Nginxui Nginx Ui
CVE-2024-49368Same product: Nginxui Nginx Ui
CVE-2024-49367Same product: Nginxui Nginx Ui
CVE-2026-33029Same product: Nginxui Nginx Ui

Affected Assets

nginxui
nginx ui
≤ 2.3.5

Mitigating Controls

Control response

Prevent
Stop it (NIST 800-53)

—

Detect
Catch it (NIST detect / respond)

—

Harden
Shrink the surface (DISA STIG)

—

Validate
Prove the fix (OWASP ASVS)
  • V4.4.2

Mitigating Controls (NIST 800-53 r5) AI

AC-3 Access Enforcement good match

Enforces approved authorizations on logical access, which can include origin checks before accepting WebSocket connections.

AC-4 Information Flow Enforcement good match

Enforces information flow policies that can require validation of communication origins at system boundaries.

SC-23 Session Authenticity good match

Protects authenticity of communications sessions, which origin validation helps ensure for WebSocket handshakes.

SC-7 Boundary Protection partial match

Monitors and controls communications at external interfaces, directly supporting origin validation for inbound WebSocket traffic.

Mitigating Controls (NIST CSF 2.0) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.

PR.PS-06 full match
prevents

Secure SDLC practices directly require origin validation for WebSocket endpoints.

PR.AA-03 mostly match
prevents

Origin validation is a required step when authenticating WebSocket connection requests.

PR.AA-05 partial match
prevents

Enforcing authorization policy on incoming connections can require origin checks.

PR.IR-01 partial match
prevents

Network-level controls that block unauthorized logical access can mitigate missing origin checks.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

A.8.29 Security testing in development and acceptance mostly match
finds

Security testing can detect missing origin validation in WebSocket implementations.

A.8.20 Networks security partial match
degrades

Network security controls can enforce origin validation and restrict WebSocket connections to trusted sources.

A.8.21 Security of network services partial match
degrades

Secure configuration of network services can include origin checks for WebSocket endpoints.

A.8.26 Application security requirements partial match
prevents

Application security requirements can mandate origin validation for WebSocket communications.

A.8.27 Secure system architecture and engineering principles partial match
prevents

Secure architecture principles can require proper origin validation mechanisms in WebSocket implementations.

A.8.28 Secure coding partial match
prevents

Secure coding standards can explicitly require origin validation for WebSocket connections.

References