Quick answers
- Is CVE-2026-126621 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-126621 being exploited in the wild.
- How severe is CVE-2026-126621?
- High severity, with a CVSS score of 7.5, published 11 November 2026.
- Which products and versions are affected?
- Progressive Robot hMailServer 6.0.0-B1 through 6.3.7.
- Is there a fix for CVE-2026-126621?
- No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
- How is CVE-2026-126621 attacked?
- It is attacked with local access, in a hosted service.
- Am I affected by CVE-2026-126621?
- Check whether you run Progressive Robot hMailServer at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.
Technical details
The vulnerability exists because hMailServer passes TLS file paths to OpenSSL as Latin-1 bytes, but OpenSSL on Windows interprets filenames as UTF-8 first. When a path contains non-ASCII Latin-1 characters that are valid UTF-8 sequences, OpenSSL opens a different file than intended. An attacker with local filesystem access can create files at these alternate UTF-8-interpreted paths, causing the server to load the attacker's certificates, private keys, or Diffie-Hellman parameters instead of the legitimate ones.
Affected products
- Progressive Robot hMailServer 6.0.0-B1 through 6.3.7
Timeline
- 2026-11-11: disclosed