Quick answers
- Is CVE-2026-126623 exploited in the wild?
- No. Junglewise Threat Intelligence has no report of CVE-2026-126623 being exploited in the wild.
- How severe is CVE-2026-126623?
- High severity, with a CVSS score of 7.5, published 11 November 2026.
- Which products and versions are affected?
- Progressive Robot hMailServer 6.3.6, 6.3.7.
- Is there a fix for CVE-2026-126623?
- 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-2026-126623 attacked?
- It is attacked over the network, in a hosted service.
- Am I affected by CVE-2026-126623?
- 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 stems from inefficient algorithmic complexity in JSON parsing where member name hashing uses a non-randomized hash function, allowing attackers to craft JSON objects where all names collide in the same hash bucket, causing quadratic-time lookups. Unauthenticated remote attackers can trigger the parser via TLS-RPT reports (up to 16 MB decompressed) sent to report mailboxes, or through password-protected message replies when the REST API is enabled; authenticated users can exploit it through webmail routes or the send API, each request consuming a worker thread and causing denial of service.
Affected products
- Progressive Robot hMailServer 6.3.6, 6.3.7
Timeline
- 2026-11-11: disclosed