# CVE-2026-33586: Authenticated SMTP Sender Address Forgery

> Authenticated users can forge sender addresses to impersonate any OVH-hosted domain, bypassing SPF validation due to default mail server configurations.

- **Severity:** Medium 6.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:N/SI:H/SA:N/E:A`)
- **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:** 7 Oct 2026
- **Updated:** 7 Oct 2026
- **Also known as:** GHSA-rpc3-43rh-hpm4

## What is CVE-2026-33586?

CVE-2026-33586 is a medium-severity vulnerability in OVHcloud, published on 7 Oct 2026. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

Authenticated users are able to manipulate both the SMTP
envelope “Envelope-from” and “From” fields when sending
emails through OVH mail servers.

Due to OVH's default SPF configuration, which
commonly includes include:mx.ovh.com, any authenticated user with a
valid OVH email account can send messages that appear to originate from any
OVH-hosted domains using the default SPF record. Since the SPF policy
explicitly authorizes OVH mail servers (mx.ovh.com) to send mail on behalf of
these domains, forged messages successfully pass SPF validation despite
not being authorized by the impersonated domain owner.

Weakness: CWE-346 (Origin Validation Error), CWE-290 (Authentication Bypass by Spoofing), CWE-1188 (Initialization of a Resource with an Insecure Default)

## Which versions are affected by CVE-2026-33586?


## How do I fix CVE-2026-33586?

No fix has been published for CVE-2026-33586 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-33586 being exploited?

There is no known exploitation of CVE-2026-33586 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33586 and fix it if it is affected.

What it is: CVE-2026-33586 is a medium-severity vulnerability in OVHcloud, published on 7 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-2026-33586 in the wild and no public exploit code.

Affected product: OVHcloud. 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-2026-33586/ (Markdown: https://insights.sbomify.com/CVE-2026-33586/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33586
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33586
- OSV: https://osv.dev/vulnerability/CVE-2026-33586

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33586/
Summaries are generated and may contain mistakes; the official description above is the record.