# CVE-2026-126613: Progressive Robot hMailServer JSON reader resource exhaustion

Source: https://junglewise.ai/threats/cve-2026-126613-allocation-of-resources-without-limits-in-the-json-reader-of  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-11-11. Updated: 2026-11-11  
License: CC BY 4.0 with a link back

CVE-2026-126613 · Severity: high · CVSS 7.5 · Published 2026-11-11

hMailServer is a mail server that handles email delivery, webmail access, and REST API operations. A flaw in its JSON reader allows remote attackers to send specially crafted JSON documents that consume excessive memory and freeze processing threads, causing mail delivery and webmail to become unavailable. Attackers can reach this flaw through email, password-protected message replies, or webmail when the REST API is enabled.

Technologies: [Progressive Robot hMailServer](https://junglewise.ai/threats/technologies/hmailserver). Vendors: [Progressive Robot](https://junglewise.ai/threats/vendors/progressive-robot).

## Quick answers

**Is CVE-2026-126613 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-126613 being exploited in the wild.

**How severe is CVE-2026-126613?** High severity, with a CVSS score of 7.5, published 11 November 2026.

**Which products and versions are affected?** Progressive Robot hMailServer 6.3.2 through 6.3.7.

**Is there a fix for CVE-2026-126613?** Yes: fixed in 6.3.8 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-126613 attacked?** It is attacked over the network, in a hosted service.

**Am I affected by CVE-2026-126613?** 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.

## How to fix

- Fixed in 6.3.8 or later

## Technical details

The JSON reader in hMailServer 6.3.2–6.3.7 lacks bounds on value allocation and recursively copies values into each parent level, allowing a single JSON document under 16 MB to consume ~2 GB of memory and block threads for seconds to minutes. Remote unauthenticated attackers can trigger this via TLS-RPT reports sent to report mailboxes (6.3.4+), password-protected message replies when the REST API is enabled (6.3.4+), or through webmail send/draft routes (6.3.2+) and other routes (6.3.4+). Multiple concurrent requests exhaust system memory and crash the entire service.

## Affected products

- Progressive Robot hMailServer 6.3.2 through 6.3.7

## Timeline

- 2026-11-11: disclosed

## Related threats

- [Progressive Robot hMailServer denial of service in web services listener](https://junglewise.ai/threats/cve-2026-126626-the-web-services-listener-of-progressive-robot-hmailserver-6-3-3)
- [hMailServer Windows installer privilege escalation via insecure folder permissions](https://junglewise.ai/threats/cve-2026-126625-incorrect-default-permissions-in-the-windows-installer-of)
- [hMailServer Windows installer privilege escalation in Bin folder](https://junglewise.ai/threats/cve-2026-126624-unverified-ownership-in-the-windows-installer-of-progressive)
- [Progressive Robot hMailServer inefficient JSON parsing DoS](https://junglewise.ai/threats/cve-2026-126623-inefficient-algorithmic-complexity-in-the-json-reader-of)
- [Progressive Robot hMailServer incorrect default installer permissions](https://junglewise.ai/threats/cve-2026-126622-incorrect-default-permissions-in-the-windows-installer-of)