CVE-2026-116606: Barracuda Networks Barracuda Email Security Gateway (ESG) flaw exploited in the wild

An authentication bypass in Barracuda Email Security Gateway versions earlier than 9.4.0.030 allows an unauthenticated remote attacker to invoke a configuration-import function and restore a crafted, compatible backup archive, resulting in unauthorized modification of the appliance’s global configuration.

• Severity: CRITICAL (CVSS 4.0 9.3, vector CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N).
• Weakness: CWE-288.
• NVD published 2026-11-02, status Undergoing Analysis.

Anyone running Barracuda Networks Barracuda Email Security Gateway (ESG). Internet-facing instances are the priority.

NVD has not published affected version ranges for this CVE yet. Use the vendor advisory in the sources below to confirm which builds are affected.

• Exploited in the wild: added to the CISA Known Exploited Vulnerabilities catalog on 2026-11-10; federal remediation due date 2026-11-13.

CISA added CVE-2026-116606 to its Known Exploited Vulnerabilities catalog on 2026-11-10. A KEV listing means CISA has evidence that attackers are using the flaw against real systems, not just that it could be used.

If your business runs Barracuda Networks Barracuda Email Security Gateway (ESG), put this at the top of the patch list. CISA gave US federal agencies until 2026-11-13 to deal with it, and that is a sensible deadline for a small business too.

• Patch. Install the latest update from Barracuda Networks. NVD does not list a fixed version, so the vendor advisory linked on this page is the reference for which release closes it.
• If you cannot patch yet. Follow CISA's required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
• Check your exposure. Find out whether Barracuda Networks Barracuda Email Security Gateway (ESG) can be reached from the internet, for example a VPN portal, an admin login page or a file-transfer site. Your firewall's port-forwarding rules and your IT provider's list of public-facing systems are the quickest places to look. Exposed copies come first.
• When to call IT support. Call your IT support provider now if you run Barracuda Networks Barracuda Email Security Gateway (ESG) and cannot confirm it is updated, if it was reachable from the internet before you patched it, or if you notice accounts, sign-ins or files you do not recognise. The last two can mean the system was already hit, and checking that properly takes someone who can read the logs.

• EPSS (probability of exploitation activity in the next 30 days): 1.60%, higher than 76% of all scored CVEs (as of 2026-11-10).
• CVERadar threat level: 62/100 (see methodology).
• Likely ATT&CK techniques: T1190 Exploit Public-Facing Application (inferred); T1078 Valid Accounts (inferred).

1. Find every instance. List where Barracuda Networks Barracuda Email Security Gateway (ESG) runs, including test, DR and forgotten internet-facing systems, and record the installed version.
2. Apply the latest vendor update. NVD does not list a fixed version, so follow the vendor advisory for the patched release.
3. If you can't patch today, follow CISA's required action: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.
4. Verify the fix. Re-run the version check on every instance and confirm it reports the fixed build. Re-scan from outside if the service is exposed.
5. Hunt for signs of earlier compromise. If the system was exposed before you patched, assume it may have been hit and check the items below.
6. Rotate credentials stored on or used by the affected system if you cannot rule out compromise, and keep the logs you reviewed.

Detection hints

• T1190 Exploit Public-Facing Application: Review WAF, reverse-proxy and application logs for unusual requests to Barracuda Email Security Gateway (ESG) (odd paths, oversized or encoded payloads, bursts of errors), going back to at least 2026-11-02.
• T1078 Valid Accounts: Check for logins from new sources or accounts you did not create.

Detection commands are generic starting points, not CVE-specific signatures. Use the indicators from the vendor advisory when it publishes them.

• NVD: CVE-2026-116606 nvd.nist.gov/vuln/detail/CVE-2026-116606
• CVE.org record www.cve.org/CVERecord?id=CVE-2026-116606
• Vendor link from CISA KEV trust.barracuda.com/security/pre-authentication-authorization-bypass-c
• Vendor link from CISA KEV github.com/mandiant/Vulnerability-Disclosures/blob/master/2026/MNDT-20
• CISA KEV catalog www.cisa.gov/known-exploited-vulnerabilities-catalog
• FIRST EPSS (2026-11-10) api.first.org/data/v1/epss?cve=CVE-2026-116606