55 lines
1.8 KiB
Diff
55 lines
1.8 KiB
Diff
https://lists.mindrot.org/pipermail/openssh-unix-dev/2024-July/041431.html
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https://www.opennet.ru/opennews/art.shtml?num=61470
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Regarding the race condition fixed in OpenSSH 9.8. A mitigation to
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prevent exploitation of this bug is to disable the login grace timer
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by setting LoginGraceTime=0 in sshd_config. This will however make
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it much easier for an attacker to deny service to sshd.
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Similarly, the much more minor keystroke timing bug can be avoided
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by disabling the feature using ObscureKeystrokeTiming=0.
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Some users will understandably prefer to patch their OpenSSH rather
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than upgrade to the newest version, so here are minimal patches for
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both problems.
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1) Critical race condition in sshd
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diff --git a/log.c b/log.c
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index 9fc1a2e2e..191ff4a5a 100644
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--- a/log.c
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+++ b/log.c
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@@ -451,12 +451,14 @@ void
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sshsigdie(const char *file, const char *func, int line, int showfunc,
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LogLevel level, const char *suffix, const char *fmt, ...)
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{
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+#ifdef SYSLOG_R_SAFE_IN_SIGHAND
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va_list args;
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va_start(args, fmt);
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sshlogv(file, func, line, showfunc, SYSLOG_LEVEL_FATAL,
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suffix, fmt, args);
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va_end(args);
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+#endif
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_exit(1);
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}
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2) Minor logic error in ObscureKeystrokeTiming
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diff --git a/clientloop.c b/clientloop.c
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index 8ec36af94..6dcd6c853 100644
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--- a/clientloop.c
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+++ b/clientloop.c
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@@ -608,8 +608,9 @@ obfuscate_keystroke_timing(struct ssh *ssh, struct timespec *timeout,
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if (timespeccmp(&now, &chaff_until, >=)) {
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/* Stop if there have been no keystrokes for a while */
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stop_reason = "chaff time expired";
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- } else if (timespeccmp(&now, &next_interval, >=)) {
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- /* Otherwise if we were due to send, then send chaff */
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+ } else if (timespeccmp(&now, &next_interval, >=) &&
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+ !ssh_packet_have_data_to_write(ssh)) {
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+ /* If due to send but have no data, then send chaff */
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if (send_chaff(ssh))
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nchaff++;
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}
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