SMTP Credential Attacks
Exploiting SMTP authentication weaknesses via brute force, credential stuffing, and relay abuse to gain unauthorized mail server access.
Mar 29, 2026
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2 min read
SMTP:
Exploitation
Guides on relay abuse, spoofed email delivery, and auth brute force
2 guides
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Created Dec 28, 2025
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Updated Mar 29, 2026
SMTP Relay Exploitation
Mar 29, 2026
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1 min read
SMTP exploitation turns a mail server into an attack platform. Open relay abuse lets you send spoofed emails from the target's own domain, bypassing SPF checks for internal phishing. Credential brute-forcing with Hydra or nxc against AUTH LOGIN and AUTH PLAIN can hand you valid mailbox credentials, especially when password policies are weak.
Known CVEs in MTAs like Exim (CVE-2019-10149 for RCE), Haraka (command injection through email headers), and older Postfix/Sendmail builds provide direct remote code execution when the version is right. Shellshock-era SMTP vectors exploited bash through mail delivery scripts. Always check the MTA version from enumeration against public exploit databases.
Successful exploitation here gives you email access for credential harvesting, a relay for further phishing, or a full shell on the mail server itself.