# CVE-2026-103010: Heap-based Buffer Overflow in hMailServer

> A local attacker can trigger a heap buffer overflow in hMailServer via an unauthenticated COM method, potentially achieving code execution as LocalSystem.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 8 Oct 2026
- **Updated:** 8 Oct 2026
- **Also known as:** GHSA-mgwr-8mph-vj23

## What is CVE-2026-103010?

CVE-2026-103010 is a high-severity memory corruption vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

Heap-based buffer overflow in the legacy Blowfish decryption routine (BlowFishEncryptor::DecryptFromString) in Progressive Robot hMailServer 6.0.0 through 6.3.3 on Windows allows a local interactive user with no hMailServer credentials to write bytes of their choosing past the end of a 255-byte heap buffer in the hMailServer service process, which runs as LocalSystem by default. The user does this by passing a long hexadecimal string to the COM method Utilities.BlowfishDecrypt, which checked no authentication. The routine converted hexadecimal input of any length into a fixed 255-byte buffer before decrypting it in place. The result is a denial of service (service crash), and possibly code execution with the privileges of the service account.

Weakness: CWE-122 (Heap-based Buffer Overflow)

## Which versions are affected by CVE-2026-103010?


## How do I fix CVE-2026-103010?

No fix has been published for CVE-2026-103010 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-103010 being exploited?

There is no known exploitation of CVE-2026-103010 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-103010 and fix it if it is affected.

What it is: CVE-2026-103010 is a high-severity memory corruption vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-103010 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-2026-103010/ (Markdown: https://insights.sbomify.com/CVE-2026-103010/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-103010
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-103010
- OSV: https://osv.dev/vulnerability/CVE-2026-103010

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-103010/
Summaries are generated and may contain mistakes; the official description above is the record.