🛡️ Google GCE Network allows unrestricted SMTP traffic🟢
- Contextual name: 🛡️ GCE Network allows unrestricted SMTP traffic🟢
- ID:
/ce/ca/google/vpc/network-smtp-access - Tags:
- Policy Type:
COMPLIANCE_POLICY - Policy Categories:
SECURITY
Logic
Description
Description
This policy identifies Google GCE Networks that have Firewall Rules allowing unrestricted incoming traffic (
0.0.0.0/0) from the internet to the Simple Mail Transfer Protocol (SMTP) port,TCP 25.In GCP, Firewall Rules are defined at the VPC Network level. Each rule either allows or denies traffic based on its configuration. These configurations specify the type of traffic (e.g., protocols and ports) and the source or destination (e.g., IP addresses, subnets, and instances).
Rationale
Exposing an SMTP server to the public internet creates substantial security and operational risks. Open or misconfigured mail relays are frequently exploited by attackers and spammers to distribute large volumes of unsolicited or malicious email. Such abuse can quickly lead to the server’s IP address being blocklisted, disrupting legitimate mail delivery and damaging domain reputation. Additionally, public SMTP ports are often targeted for reconnaissance and exploitation attempts against mail server software vulnerabilities.
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Remediation
Remediation
From Google Cloud Console
- Go to
VPC Network.- Go to the
Firewall Rules.- Click the
Firewall Ruleto be modified.- Click
Edit.- Modify
Source IP rangesto specificIP.- Click
Save.From Google Cloud CLI
Identify Firewall Rules Allowing Public Access
gcloud compute networks get-effective-firewalls default \
--format="table(NAME, DIRECTION, IP_RANGES)" \
--filter="IP_RANGES:0.0.0.0/0 AND DIRECTION:INGRESS"Restrict the Source Range
Once you have identified the firewall rules, update each one to restrict access to trusted CIDR ranges:
gcloud compute firewall-rules update {{firewall-rule-name}} \
--source-ranges={{cidr-range1}},{{cidr-range2}}