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.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
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.
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.
Sources
Also known as GHSA-rpc3-43rh-hpm4.