aws-lc: not enforcing server cipher order for TLS v1.3 #3024
Description
Detailed Description of the Problem
Wth aws-ls HAProxy is not only enforcing cipher order for TLS v1.3 ciphers, but it seems like it's not even setting the ciphers. The result is that https client manages to negotiate the weakest ciphersuite TLS_AES_128_GCM_SHA256 even in cases when that's not the only cipher supported by the client.
Bellow is an output from testssl.sh when aws-lc is used with HAProxy. Note the Has server cipher order? line.
Testing server's cipher preferences
Hexcode Cipher Suite Name (OpenSSL) KeyExch. Encryption Bits Cipher Suite Name (IANA/RFC)
-----------------------------------------------------------------------------------------------------------------------------
SSLv2
-
SSLv3
-
TLSv1
-
TLSv1.1
-
TLSv1.2 (server order)
xcca9 ECDHE-ECDSA-CHACHA20-POLY1305 ECDH 253 ChaCha20 256 TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256
xc02c ECDHE-ECDSA-AES256-GCM-SHA384 ECDH 253 AESGCM 256 TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
xc02b ECDHE-ECDSA-AES128-GCM-SHA256 ECDH 253 AESGCM 128 TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
xcca8 ECDHE-RSA-CHACHA20-POLY1305 ECDH 253 ChaCha20 256 TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256
xc030 ECDHE-RSA-AES256-GCM-SHA384 ECDH 253 AESGCM 256 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
xc02f ECDHE-RSA-AES128-GCM-SHA256 ECDH 253 AESGCM 128 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
TLSv1.3 (no server order, thus listed by strength)
x1302 TLS_AES_256_GCM_SHA384 ECDH/MLKEM AESGCM 256 TLS_AES_256_GCM_SHA384
x1303 TLS_CHACHA20_POLY1305_SHA256 ECDH/MLKEM ChaCha20 256 TLS_CHACHA20_POLY1305_SHA256
x1301 TLS_AES_128_GCM_SHA256 ECDH/MLKEM AESGCM 128 TLS_AES_128_GCM_SHA256
Has server cipher order? yes (OK) -- only for < TLS 1.3
Expected Behavior
Bellow is the output of testssh.sh when openssl is used.
Testing server's cipher preferences
Hexcode Cipher Suite Name (OpenSSL) KeyExch. Encryption Bits Cipher Suite Name (IANA/RFC)
-----------------------------------------------------------------------------------------------------------------------------
SSLv2
-
SSLv3
-
TLSv1
-
TLSv1.1
-
TLSv1.2 (server order)
xcca9 ECDHE-ECDSA-CHACHA20-POLY1305 ECDH 253 ChaCha20 256 TLS_ECDHE_ECDSA_WITH_CHACHA20_POLY1305_SHA256
xc02c ECDHE-ECDSA-AES256-GCM-SHA384 ECDH 253 AESGCM 256 TLS_ECDHE_ECDSA_WITH_AES_256_GCM_SHA384
xc02b ECDHE-ECDSA-AES128-GCM-SHA256 ECDH 253 AESGCM 128 TLS_ECDHE_ECDSA_WITH_AES_128_GCM_SHA256
xcca8 ECDHE-RSA-CHACHA20-POLY1305 ECDH 253 ChaCha20 256 TLS_ECDHE_RSA_WITH_CHACHA20_POLY1305_SHA256
xc030 ECDHE-RSA-AES256-GCM-SHA384 ECDH 253 AESGCM 256 TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384
xc02f ECDHE-RSA-AES128-GCM-SHA256 ECDH 253 AESGCM 128 TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256
TLSv1.3 (server order)
x1302 TLS_AES_256_GCM_SHA384 ECDH/MLKEM AESGCM 256 TLS_AES_256_GCM_SHA384
x1303 TLS_CHACHA20_POLY1305_SHA256 ECDH/MLKEM ChaCha20 256 TLS_CHACHA20_POLY1305_SHA256
x1301 TLS_AES_128_GCM_SHA256 ECDH/MLKEM AESGCM 128 TLS_AES_128_GCM_SHA256
Has server cipher order? yes (OK) -- TLS 1.3 and below
Steps to Reproduce the Behavior
Compile aws-lc 1.54.0 and compile HAproxy 3.2.1 with SSL flags to point at aws-lc headers and binaries, such as SSL_INC=/opt/aws-lc/include SSL_LIB=/opt/aws-lc/lib.
Start up the HAProxy server and run testssl.sh against it.
Do you have any idea what may have caused this?
Most likely due to HAProxy not using SSL_OP_CIPHER_SERVER_PREFERENCE flag at runtime for aws-lc.
Do you have an idea how to solve the issue?
I'd suggest using SSL_OP_CIPHER_SERVER_PREFERENCE flag in HAProxy code at runtime when aws-lc is used.
What is your configuration?
global
log /dev/log local0
stats socket /var/run/haproxy.sock mode 660 expose-fd listeners level admin
ssl-default-bind-ciphers ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-ARIA256-GCM-SHA384:ECDHE-ARIA256-GCM-SHA384:DHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-CCM8:ECDHE-ECDSA-AES256-CCM:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES128-GCM-SHA256
#ssl-default-bind-ciphers CHACHA20:AESGCM:AESCCM8:AESCCM:AES:ECDSA:RSA:DES:!DHE:!aNULL:!eNULL:!EXP:!LOW:!MD5:!PSK:!DSS:!CAMELLIA:!ARIA
ssl-default-bind-ciphersuites TLS_CHACHA20_POLY1305_SHA256:TLS_AES_256_GCM_SHA384:TLS_AES_128_GCM_SHA256:TLS_AES_128_CCM_SHA256:TLS_AES_128_CCM_8_SHA256
ssl-default-bind-options ssl-min-ver TLSv1.2
ssl-default-bind-curves X25519MLKEM768:SecP384r1MLKEM1024:SecP256r1MLKEM768:X25519:P-521:P-384
ssl-default-server-ciphers ECDHE-ECDSA-CHACHA20-POLY1305:ECDHE-ECDSA-AES256-GCM-SHA384:ECDHE-RSA-CHACHA20-POLY1305:ECDHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-ARIA256-GCM-SHA384:ECDHE-ARIA256-GCM-SHA384:DHE-RSA-CHACHA20-POLY1305:DHE-RSA-AES256-GCM-SHA384:ECDHE-ECDSA-AES256-CCM8:ECDHE-ECDSA-AES256-CCM:ECDHE-ECDSA-AES128-GCM-SHA256:ECDHE-RSA-AES128-GCM-SHA256:DHE-RSA-AES128-GCM-SHA256
ssl-default-server-ciphersuites TLS_CHACHA20_POLY1305_SHA256:TLS_AES_256_GCM_SHA384:TLS_AES_128_GCM_SHA256:TLS_AES_128_CCM_SHA256:TLS_AES_128_CCM_8_SHA256
ssl-default-server-options ssl-min-ver TLSv1.2
ssl-default-server-curves X25519MLKEM768:X25519:P-521:P-384
#ssl-dh-param-file /etc/haproxy/certs/dh/dhparam4096.pem
ocsp-update.mode on
...Output of haproxy -vv
HAProxy version 3.2.1-f4d1a4e 2025/06/11 - https://haproxy.org/
Status: long-term supported branch - will stop receiving fixes around Q2 2030.
Known bugs: http://www.haproxy.org/bugs/bugs-3.2.1.html
Running on: Linux 6.15.2-arch1-1 #1 SMP PREEMPT_DYNAMIC Tue, 10 Jun 2025 21:32:33 +0000 x86_64
Build options :
TARGET = linux-glibc
CC = cc
CFLAGS = -O2 -g -fwrapv -O3 -g -Wall -Wextra -Wundef -Wdeclaration-after-statement -Wfatal-errors -Wtype-limits -Wshift-negative-value -Wshift-overflow=2 -Wduplicated-cond -Wnull-dereference -fwrapv -Wno-address-of-packed-member -Wno-unused-label -Wno-sign-compare -Wno-unused-parameter -Wno-clobbered -Wno-missing-field-initializers -Wno-cast-function-type -Wno-string-plus-int -Wno-atomic-alignment
OPTIONS = USE_THREAD=1 USE_LIBCRYPT=1 USE_GETADDRINFO=1 USE_OPENSSL_AWSLC=1 USE_ZLIB= USE_SLZ=1 USE_NS=1 USE_QUIC=1 USE_PCRE= USE_PCRE_JIT= USE_PCRE2=1 USE_PCRE2_JIT=1
DEBUG =
Feature list : -51DEGREES +ACCEPT4 +BACKTRACE -CLOSEFROM +CPU_AFFINITY +CRYPT_H -DEVICEATLAS +DL -ENGINE +EPOLL -EVPORTS +GETADDRINFO -KQUEUE -LIBATOMIC +LIBCRYPT +LINUX_CAP +LINUX_SPLICE +LINUX_TPROXY -LUA -MATH -MEMORY_PROFILING +NETFILTER +NS -OBSOLETE_LINKER +OPENSSL +OPENSSL_AWSLC -OPENSSL_WOLFSSL -OT -PCRE +PCRE2 +PCRE2_JIT -PCRE_JIT +POLL +PRCTL -PROCCTL -PROMEX -PTHREAD_EMULATION +QUIC -QUIC_OPENSSL_COMPAT +RT +SLZ +SSL -STATIC_PCRE -STATIC_PCRE2 +TFO +THREAD +THREAD_DUMP +TPROXY -WURFL -ZLIB
Default settings :
bufsize = 16384, maxrewrite = 1024, maxpollevents = 200
Built with multi-threading support (MAX_TGROUPS=32, MAX_THREADS=1024, default=2).
Built with SSL library version : OpenSSL 1.1.1 (compatible; AWS-LC 1.54.0)
Running on SSL library version : AWS-LC FIPS 1.54.0
SSL library supports TLS extensions : yes
SSL library supports SNI : yes
SSL library FIPS mode : yes
SSL library supports : TLSv1.0 TLSv1.1 TLSv1.2 TLSv1.3
QUIC: connection socket-owner mode support : yes
QUIC: GSO emission support : yes
Built with network namespace support.
Built with libslz for stateless compression.
Compression algorithms supported : identity("identity"), deflate("deflate"), raw-deflate("deflate"), gzip("gzip")
Built with transparent proxy support using: IP_TRANSPARENT IPV6_TRANSPARENT IP_FREEBIND
Built with PCRE2 version : 10.42 2022-12-11
PCRE2 library supports JIT : yes
Encrypted password support via crypt(3): yes
Built with gcc compiler version 15.1.0
Available polling systems :
epoll : pref=300, test result OK
poll : pref=200, test result OK
select : pref=150, test result OK
Total: 3 (3 usable), will use epoll.
Available multiplexer protocols :
(protocols marked as <default> cannot be specified using 'proto' keyword)
quic : mode=HTTP side=FE mux=QUIC flags=HTX|NO_UPG|FRAMED
h2 : mode=HTTP side=FE|BE mux=H2 flags=HTX|HOL_RISK|NO_UPG
<default> : mode=HTTP side=FE|BE mux=H1 flags=HTX
h1 : mode=HTTP side=FE|BE mux=H1 flags=HTX|NO_UPG
fcgi : mode=HTTP side=BE mux=FCGI flags=HTX|HOL_RISK|NO_UPG
<default> : mode=SPOP side=BE mux=SPOP flags=HOL_RISK|NO_UPG
spop : mode=SPOP side=BE mux=SPOP flags=HOL_RISK|NO_UPG
<default> : mode=TCP side=FE|BE mux=PASS flags=
none : mode=TCP side=FE|BE mux=PASS flags=NO_UPG
Available services : none
Available filters :
[BWLIM] bwlim-in
[BWLIM] bwlim-out
[CACHE] cache
[COMP] compression
[FCGI] fcgi-app
[SPOE] spoe
[TRACE] trace
Last Outputs and Backtraces
None.
Additional Information
None.