# CVE-2026-103011: Heap-based Buffer Overflow in hMailServer

> Authenticated users or local attackers can trigger a heap buffer overflow in hMailServer's legacy encryption, causing crashes or potential code execution.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 8 Oct 2026
- **Updated:** 8 Oct 2026
- **Also known as:** GHSA-46vr-9694-qxgc

## What is CVE-2026-103011?

CVE-2026-103011 is a medium-severity memory corruption vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Heap-based buffer overflow in the legacy Blowfish encryption routine (BlowFishEncryptor::Encode, called by EncryptToString) in Progressive Robot hMailServer 6.0.0 through 6.3.5 allows an authenticated mailbox user to cause a denial of service (service crash), and possibly other unspecified impact. In 6.3.4 and 6.3.5, where the self-service REST API is enabled (it is off by default), the user does this remotely by adding a fetch account whose password is 129 to 247 characters long and not a multiple of 8, and then requesting their personal data export (GET /api/v1/me/export.zip), which encrypts that password with the legacy scheme. The same flaw is reachable on Windows by any local interactive user with no hMailServer credentials, through the COM method Utilities.BlowfishEncrypt, which checked no authentication. It is also reachable by every stored-secret write when ProtectStoredSecretsWithDPAPI is set to 0. For such a length, the routine's padding loop writes up to 7 zero bytes 2 to 232 bytes past the end of its 255-byte heap buffer. The ciphertext it returns is still correct.

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

## Which versions are affected by CVE-2026-103011?


## How do I fix CVE-2026-103011?

No fix has been published for CVE-2026-103011 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-103011 being exploited?

There is no known exploitation of CVE-2026-103011 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-103011 and fix it if it is affected.

What it is: CVE-2026-103011 is a medium-severity memory corruption vulnerability in Progressive Robot Ltd hMailServer, published on 8 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-103011 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-2026-103011/ (Markdown: https://insights.sbomify.com/CVE-2026-103011/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-103011
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-103011
- OSV: https://osv.dev/vulnerability/CVE-2026-103011

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-103011/
Summaries are generated and may contain mistakes; the official description above is the record.