Bug 2511440

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A command injection vulnerability exists in the linux_sockets PMDA through the
writable metric network.persocket.filter. The validation helper sockets_check_filter() returns
1 for safe input and 0 for unsafe input, but the store handler uses an inverted condition: safe
expressions are rejected while malicious ones containing shell metacharacters are silently
accepted. The attacker-controlled filter value is later incorporated into a shell command
executed via popen() whenever socket metrics are refreshed, enabling arbitrary command
execution as the PMDA process user.
Prerequisites:
• linux_sockets PMDA loaded;
• ss binary present (/usr/sbin/ss or /usr/bin/ss);
• no [access] section restricting pmstore in pmcd.conf (default behavior).