# CVE-2026-107579: Inefficient Algorithmic Complexity in hMailServer

> Remote attackers can cause denial of service in hMailServer by sending crafted messages that trigger inefficient processing, requiring bounce or complaint features to be enabled.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 8 Oct 2026
- **Updated:** 8 Oct 2026
- **Also known as:** GHSA-7658-76c6-34x2

## What is CVE-2026-107579?

CVE-2026-107579 is a high-severity denial of service vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

Inefficient algorithmic complexity in the bounce and complaint processing of Progressive Robot hMailServer 6.3.4 and 6.3.5 allows a remote unauthenticated attacker to stop mail delivery by sending messages, when bounce processing or complaint processing is enabled or a mailing list is managed by the server (none is by default). The readers of incoming delivery status notifications (RFC 3464) and abuse feedback reports (RFC 5965) removed the blank lines at the start of the returned headers part two bytes at a time, copying the rest of the part each time, so their work grew with the square of the number of blank lines. A message shaped like such a report, whose headers part begins with a very large number of blank lines within the reader's 2 MB limit, keeps a delivery thread busy for over a minute while it is delivered, and a few such messages a minute keep every delivery thread busy.

Weakness: CWE-407 (Inefficient Algorithmic Complexity)

## Which versions are affected by CVE-2026-107579?


## How do I fix CVE-2026-107579?

No fix has been published for CVE-2026-107579 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-107579 being exploited?

There is no known exploitation of CVE-2026-107579 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-107579 and fix it if it is affected.

What it is: CVE-2026-107579 is a high-severity denial of service vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-107579 in the wild and no public exploit code.

Affected product: Progressive Robot Ltd hMailServer. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-107579/ (Markdown: https://insights.sbomify.com/CVE-2026-107579/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-107579
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-107579
- OSV: https://osv.dev/vulnerability/CVE-2026-107579

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-107579/
Summaries are generated and may contain mistakes; the official description above is the record.