Remote Code Execution via Shell Injection in qmail-remote TLS Error Handler#42
Merged
sagredo-dev merged 2 commits intomainfrom Apr 7, 2026
Merged
Remote Code Execution via Shell Injection in qmail-remote TLS Error Handler#42sagredo-dev merged 2 commits intomainfrom
sagredo-dev merged 2 commits intomainfrom
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Thanks to Diep Pham, who spotted this vulnerability.
When an outbound TLS handshake fails,
qmail-remoteautomatically records the remote hostname in a blocklist file by executing a shell command constructed from the unsanitized DNS MX exchange name. An attacker who controls DNS records for a domain can embed shell metacharacters in the MX hostname, achieving arbitrary command execution on the mail server as theqmailruser. The vulnerability requires thecontrol/notlshosts_autofeature to be enabled (a documented production feature for handling broken TLS hosts) and for the victim server to send or relay email to the attacker-controlled domain.