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Address missing extended_master secret extension properly #3029

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Merged
drwetter merged 1 commit into from
Apr 20, 2026
+26 −21
Merged

Address missing extended_master secret extension properly #3029

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47 changes: 26 additions & 21 deletions testssl.sh
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Original file line number Diff line number Diff line change
Expand Up @@ -10693,8 +10693,9 @@ run_server_defaults() {
outln "(none)"
fileout "TLS_extensions" "INFO" "(none)"
else
#FIXME: we rather want to have the chance to print each ext in italics or another format.
# Atm is a string of quoted strings -- that needs to be fixed at the root then
#FIXME: we rather want to print each ext in italics or another format.
# Atm it's a string of quoted strings -- that needs to be fixed at the
# the root then.
# out_row_aligned_max_width() places line breaks at space characters.
# So, in order to prevent the text for an extension from being broken
# across lines, temporarily replace space characters within the text
Expand All @@ -10707,32 +10708,36 @@ run_server_defaults() {
tls_extensions="${tls_extensions:1}"
fileout "TLS_extensions" "INFO" "$tls_extensions"
tls_extensions="${tls_extensions// /{}"
tls_extensions="${tls_extensions//\"{\"/\" \"}"
tls_extensions="$(out_row_aligned_max_width "$tls_extensions" " " $TERM_WIDTH)"
tls_extensions="${tls_extensions//{/ }"
tls_extensions="${tls_extensions//'{\"'/'" "'}"
#tls_extensions="${tls_extensions//\"{\"/\" \"}" # blank command for deconfusing vim's syntax hiliting
tls_extensions="$(out_row_aligned_max_width "$tls_extensions" ' ' $TERM_WIDTH)"
tls_extensions="${tls_extensions//\{/ }"
outln "$tls_extensions"
fi

# We want to check whether the (for >=TLS 1.2) mandatory "extended master secret" extension is supported by
# the server. Otherwise it would violate RFC 9325 https://www.rfc-editor.org/rfc/rfc9325#section-3.5
# and cause connection problems.
# We want to check whether the (for <=TLS 1.2) mandatory "extended master secret" extension is supported by
# the server. Otherwise it would violate RFC 9325 https://www.rfc-editor.org/rfc/rfc9325#section-3.5. Also:
# "If a server implementing this document receives the "extended_master_secret" extension, it MUST
# include the extension in its ServerHello message". (https://www.rfc-editor.org/rfc/rfc7627.html#section-5.2).

jsonID="TLS_misses_extension_23"
if [[ $(has_server_protocol "tls1_2") -eq 1 ]] && [[ $(has_server_protocol "tls1_3") -eq 1 ]] ; then
:
elif [[ $tls_extensions =~ \#23 ]]; then
# Was the last handshake >= TLS 1.2 ?
if grep -qE 'Protocol.*(TLSv1.3|TLSv1.2)' $TEMPDIR/$NODEIP.parse_tls_serverhello.txt ; then
fileout "$jsonID" "INFO" "Extended master secret extension detected"
debugme outln "${spaces}Extended master secret extension detected"
if [[ $tls_extensions =~ \#23 ]]; then
if "$TLS13_ONLY"; then
# this shouldn't happen
fileout "$jsonID" "LOW" "Misconfiguration: Extended master secret extension detected for TLS 1.3 only"
debugme outln "${spaces}Misconfiguration: Extended master secret extension detected for TLS 1.3 only"
else
out "$spaces"
prln_warning "Fixme: Server supports TLS 1.2 or 1.3 but last ServerHello was < TLS 1.2"
fileout "$jsonID" "WARN" "Server supports TLS 1.2 or 1.3 but last ServerHello was < TLS 1.2"
if grep -qE 'Protocol.*(TLSv1.)' $TEMPDIR/$NODEIP.parse_tls_serverhello.txt ; then
fileout "$jsonID" "INFO" "Extended master secret extension detected"
debugme outln "${spaces}Extended master secret extension detected"
fi
# We don't worry about SSL3.0 here. It should have been tested before withg testssl.sh --
# though it's mentioned in https://www.rfc-editor.org/rfc/rfc7627.html#section-6.4
fi
else
elif ! "$TLS13_ONLY"; then
out "$spaces"
prln_svrty_medium "No extended master secret extension, violates RFC 9325 & may cause connection problems"
fileout "$jsonID" "MEDIUM" "No extended master secret extension, violates RFC 9325 & may cause connection problems"
prln_svrty_medium "No extended master secret extension, violates RFC 7627/9325 & may cause connection problems"
fileout "$jsonID" "MEDIUM" "No extended master secret extension, violates RFC 7627/9325 & may cause connection problems"
fi

pr_bold " Session Ticket RFC 5077 hint "
Expand Down