Authenticated SMTP Sender Address Forgery

published 2026-10-07 last mo. modified 2026-10-08 last mo. also EUVD-2026-94378

cvss: 6.3; version 4.0, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.1%; EPSS 0.1% chance of exploitation in 30 days, percentile 3%
public exploits: 0; none known

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.

Patch / fix

fixed in 1

OVHcloud OVHcloud 2026-07-20

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CISA SSVC

Exploitation: none
Automatable: no
Technical impact: partial
Assessed: last mo. (2026-10-07)

Exploit prediction

0.14% chance of exploitation in the next 30 days, higher than 3% of all scored CVEs (FIRST EPSS, 2026-11-09).

CVSS scores

assigned by	version	score	vector
CNA	4.0	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
CNA	4.0	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/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Affected products

OVHcloud OVHcloud

Classification

Weakness

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

References

docs.ovhcloud.com /en/guides/web-cloud/email-and-collaborative-solutions/troubleshooting/email-rejected-cross-domain-spoofing

Sources

CVE List CVE-2026-33586
NVD CVE-2026-33586

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