# CVE-2026-2748: S/MIME Certificate Subject Whitespace

> Attackers can spoof S/MIME signatures by exploiting improper validation of certificate subjects containing whitespace in SEPPmail Secure Email Gateway.

- **Severity:** High 7.8 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:L/SI:H/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 4 Mar 2026
- **Updated:** 4 Mar 2026
- **Also known as:** GHSA-qg5v-hxpj-p53x

## What is CVE-2026-2748?

CVE-2026-2748 is a high-severity vulnerability in SEPPmail Secure Email Gateway, published on 4 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

SEPPmail Secure Email Gateway before version 15.0.1 improperly validates S/MIME certificates issued for email addresses containing whitespaces, allowing signature spoofing.

Weakness: CWE-295 (Improper Certificate Validation)

## Which versions are affected by CVE-2026-2748?

It affects 1 product.


Products: Seppmail Seppmail.

## How do I fix CVE-2026-2748?

No fix has been published for CVE-2026-2748 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-2748 being exploited?

There is no known exploitation of CVE-2026-2748 in the wild and no public exploit code.

## Other vulnerabilities in SEPPmail Secure Email Gateway

- [CVE-2026-2743](https://insights.sbomify.com/CVE-2026-2743/): SEPPmail User Web Interface Arbitrary File Write to RCE (critical 10.0)
- [CVE-2026-27441](https://insights.sbomify.com/CVE-2026-27441/): PDF Password CMDi (critical 9.5)
- [CVE-2026-27442](https://insights.sbomify.com/CVE-2026-27442/): zip_attachments Path Traversal (critical 9.3)
- [CVE-2026-27443](https://insights.sbomify.com/CVE-2026-27443/): S/MIME Decryption Tag Sanitization Bypass (high 8.2)
- [CVE-2026-27444](https://insights.sbomify.com/CVE-2026-27444/): Header Email Address Parsing (high 7.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-2748 and fix it if it is affected.

What it is: CVE-2026-2748 is a high-severity vulnerability in SEPPmail Secure Email Gateway, published on 4 Mar 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-2026-2748 in the wild and no public exploit code.

Affected product: SEPPmail Secure Email Gateway. 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-2026-2748/ (Markdown: https://insights.sbomify.com/CVE-2026-2748/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-2748
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-2748
- OSV: https://osv.dev/vulnerability/CVE-2026-2748

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-2748/
Summaries are generated and may contain mistakes; the official description above is the record.