CVE-2026-27944: Nginx-UI Vulnerable to Unauthenticated Backup Download with Encryption Key Disclosure

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 1.0%, percentile 63: FIRST’s model estimates a 1.0% chance of exploitation activity in the next 30 days, higher than 63% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes github.com/0xJacky/Nginx-UI (Go) < 2.3.3, fixed in 2.3.3. Check your lockfile, including transitive dependencies.

What it is

Nginx UI is a web user interface for the Nginx web server. Prior to version 2.3.3, the /api/backup endpoint is accessible without authentication and discloses the encryption keys required to decrypt the backup in the X-Backup-Security response header. This allows an unauthenticated attacker to download a full system backup containing sensitive data (user credentials, session tokens, SSL private keys, Nginx configurations) and decrypt it immediately. This issue has been patched in version 2.3.3.

From the GitHub advisory

Summary

The /api/backup endpoint is accessible without authentication and discloses the encryption keys required to decrypt the backup in the X-Backup-Security response header. This allows an unauthenticated attacker to download a full system backup containing sensitive data (user credentials, session tokens, SSL private keys, Nginx configurations) and decrypt it immediately.

Vulnerability Details

| Field | Value | |-------|-------| | CWE | CWE-306: Missing Authentication for Critical Function + CWE-311: Missing Encryption of Sensitive Data | | Affected File | api/backup/router.go | | Affected Function | CreateBackup (lines 8-11 in router, implementation in api/backup/backup.go:13-38) | | Secondary File | internal/backup/backup.go | | CVSS 3.1 | 9.8 (Critical) | | CVSS Vector | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H |

Root Cause

Weakness type: CWE-311, CWE-306.

Product: github.com/0xJacky/Nginx-UI (Go) · Assigned by: GitHub_M · Published: 2026-03-05

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 1.01% probability of exploitation activity in the next 30 days; percentile 63.

Timeline

• 2026-03-05 — CVE record published by GitHub_M
• 2026-03-05 — GitHub-reviewed advisory GHSA-g9w5-qffc-6762 published (critical)
• 2026-03-19 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-g9w5-qffc-6762 github.com
2. CVE.org record CVE-2026-27944 cve.org
3. NVD entry CVE-2026-27944 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. csrc.nist.gov csrc.nist.gov
3. owasp.org owasp.org
4. owasp.org owasp.org

Critical Go advisories · Today’s Security Digest