CVE-2025-62875: 
Linux Debian vulnerability analysis and mitigation

A local Denial-of-Service vulnerability (CVE-2025-62875) was discovered in OpenSMTPD version 7.7.0, affecting the UNIX domain socket functionality. The vulnerability allows unprivileged local users to crash an OpenSMTPD instance through the world-writable smtpd.sock file. The issue was discovered during a code review for openSUSE Tumbleweed packaging (OpenWall).

The vulnerability exists due to the world-writable UNIX domain socket smtpd.sock (file mode 0666) allowing any user to create local connections to smtpd. The daemon's code in mproc_dispatch() exits via fatal() when handling malformed socket connections. The issue can be triggered by sending a message with a bad header length, causing the smtpd: control instance to terminate and shut down the entire smtpd instance. Additionally, a memory leak was discovered in the socket handling code that remains unaddressed, causing continuous memory growth when multiple connections are created and closed in succession (OpenWall).

When exploited, the vulnerability allows any local user to cause a denial of service by shutting down all smtpd services. The associated memory leak can also lead to resource exhaustion over time, consuming approximately 100 megabytes of memory within half an hour of continuous exploitation (OpenWall).

A fix has been provided in upstream commit 653abf00f5283a2d3247eb9aabf8987d1b2f0510 and will be included in OpenSMTPD version 7.8.0. As a temporary workaround, system administrators can tighten the permissions of the smtpd.sock UNIX domain socket, though this may affect legitimate non-root users attempting to enqueue mail using the sendmail interface (OpenWall).

The vulnerability was initially reported to OpenBSD security team on September 15, 2025, and after a period of silence, was later shared with the distros mailing list. The OpenSMTPD developer team acknowledged the issue on October 29, 2025, explaining that the information had been internally misplaced. The response led to a coordinated fix and disclosure process (OpenWall).