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plugins/auth/pam: don't echo terminal input during the PAM fail delay - #568
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After tgetpass() reads the password it restores the terminal to its original state, which re-enables echo. When authentication fails, the PAM stack typically sleeps for a short time (the fail delay applied by pam_unix) before pam_authenticate() returns. Any input the user typed during that delay, such as re-entering the password before the next prompt, was echoed to the terminal in the clear. Disable terminal echo in the PAM conversation function once the password has been read and restore it after pam_authenticate() returns, with a safety net in sudo_pam_cleanup() to also cover the pam_chauthtok() and pam_acct_mgmt() paths. Fixes GitHub issue sudo-project#530
millert
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Oct 17, 2026
millert
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This looks like a reasonable approach and I appreciate that you used sudo_term_* instead of using tcsetattr() directly. There's always going to be a small window where a character could be echoed between tgetpass() returning disabling echo again but this is probably the best we can do.
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After tgetpass() reads the password it restores the terminal to its original state, which re-enables echo. When authentication fails, the PAM stack typically sleeps for a short time (the fail delay applied by pam_unix) before pam_authenticate() returns. Any input the user typed during that delay, such as re-entering the password before the next prompt, was echoed to the terminal in the clear.
Disable terminal echo in the PAM conversation function once the password has been read and restore it after pam_authenticate() returns, with a safety net in sudo_pam_cleanup() to also cover the pam_chauthtok() and pam_acct_mgmt() paths.
Fixes GitHub issue #530