38

I'd like to ask if there's a way to lower SSL security level to 1 on Ubuntu 20.04, since I'm receiving:

141A318A:SSL routines:tls_process_ske_dhe:dh key too small

when trying to curl the website.

Curl works if I add --ciphers 'DEFAULT:!DH' parameter, however, I am not able to fetch a website via my client app written in C#. The website also works when opened via browser.

According to bugs.launchpad.net the Ubuntu team set higher SSL security level on purpose.

In several places I came across an information that changing CipherString = DEFAULT@SECLEVEL=2 to 1 in openssl.cnf helps, but my config file did not have such a line at all and adding it had no effect.

I do not control the website server, so I am not able to change its security configuration.

Any ideas? Would installing some older openSSL package help?

Thanks in advance

EDIT: As for changes to my config file, I've added the following at the end:

system_default = system_default_sect 

[system_default_sect] 
MinProtocol = TLSv1.2
CipherString = DEFAULT@SECLEVEL=1 

Output from openssl version -a:

OpenSSL 1.1.1f 31 Mar 2020 built on: Mon Apr 20 11:53:50 2020 UTC
platform: debian-amd64
options: bn(64,64) rc4(16x,int) des(int) blowfish(ptr)
compiler: gcc -fPIC -pthread -m64 -Wa,--noexecstack -Wall -Wa,
--noexecstack -g -O2 -fdebug-prefix-map=/build/openssl-P_ODHM/openssl-1.1.1f=. 
-fstack-protector-strong -Wformat -Werror=format-security
-DOPENSSL_TLS_SECURITY_LEVEL=2 -DOPENSSL_USE_NODELETE
-DL_ENDIAN -DOPENSSL_PIC -DOPENSSL_CPUID_OBJ
-DOPENSSL_IA32_SSE2 -DOPENSSL_BN_ASM_MONT
-DOPENSSL_BN_ASM_MONT5 -DOPENSSL_BN_ASM_GF2m
-DSHA1_ASM -DSHA256_ASM -DSHA512_ASM -DKECCAK1600_ASM
-DRC4_ASM -DMD5_ASM -DAESNI_ASM -DVPAES_ASM -DGHASH_ASM
-DECP_NISTZ256_ASM -DX25519_ASM -DPOLY1305_ASM -DNDEBUG
-Wdate-time -D_FORTIFY_SOURCE=2
OPENSSLDIR: "/usr/lib/ssl" ENGINESDIR:
"/usr/lib/x86_64-linux-gnu/engines-1.1" Seeding source: os-specific
5
  • Is your C# application calling OpenSSL APIs directly? I'm not familiar with the C# OpenSSL bindings, but in C you can change the security level using SSL_CTX_set_cipher_list(ctx, "DEFAULT:@SECLEVEL=1");. Or alternatively SSL_CTX_set_security_level(ctx, 1). – Matt Caswell Apr 30 '20 at 8:09
  • Unfortunately I use a high-level class to do HTTP requests. But would it be possible to call this function from C to change security level for the whole system? – Łukasz Sypniewski Apr 30 '20 at 8:56
  • Calling it in C will only change the setting for the current process – Matt Caswell Apr 30 '20 at 9:36
  • Can you show what changes you made to your config file, and also the output from openssl version -a? – Matt Caswell Apr 30 '20 at 9:38
  • @MattCaswell I added the information you asked for to the question – Łukasz Sypniewski Apr 30 '20 at 11:37
58

You don't have your config changes quite right. You need to add this to the beginning of your config file:

openssl_conf = default_conf

And then this to the end:

[ default_conf ]

ssl_conf = ssl_sect

[ssl_sect]

system_default = system_default_sect

[system_default_sect]
MinProtocol = TLSv1.2
CipherString = DEFAULT:@SECLEVEL=1

Note that if you prefer you can make changes to a local copy of the config file, and then ensure your process is started with the environment variable OPENSSL_CONF defined to point at the location of your config file:

export OPENSSL_CONF=/path/to/my/openssl.cnf

This way you can make changes without having to impact your entire system.

Note: To find the system's openssl.cnf file, run the following:

% openssl version -d

the run ls -l on the directory outputted to see where the openssl.cnf file is via its symlink in that directory as needed.

7
  • Thanks! That fixed it for me. After upgrading from Ubuntu 18.04 LTS to 20.04 LTS my wget refused to connect to a server I had previously copied files from. With this modification of openssl.cnf it works again. – Norbert S May 30 '20 at 1:42
  • I did the updates to the openssl.cnf but still the same issue.. even after rebooting the system – johnny Jun 27 '20 at 17:45
  • Thanks, this had me stumped, the server I was having an issue with is rated A on SSL Labs, surely this is a bug? – Caleb Jun 29 '20 at 11:06
  • @Caleb good question, maybe it is not considered a security vulnerability but just a security that can be improved? – baptx Aug 6 '20 at 18:10
  • 1
    @johnny it is not working for me either, did anyone get this solution working on Ubuntu 20.04? At least I found a workaround by using the curl command in a Debian LXC container where I just need to change SECLEVEL=2 to SECLEVEL=1. Update: I shared an answer that works by using the Debian config file on Ubuntu. Update 2: in fact this solution seems to work if you extract the default configuration from the deb file by downloading it on packages.ubuntu.com/search?keywords=openssl&searchon=names. – baptx Aug 6 '20 at 18:51
6

Edit openssl.conf file:

sudo nano /etc/ssl/openssl.cnf

Add this line at the top:

openssl_conf = openssl_init

And add these lines at the end:

[openssl_init]
ssl_conf = ssl_sect

[ssl_sect]
system_default = system_default_sect

[system_default_sect]
CipherString = DEFAULT@SECLEVEL=1

It works for me. :)

Ref: When I try to CURL a website I get SSL error

1
  • Thank you!!!! 3 days of searching ODBC driver 17 SQL issues with server 2012 r2 led me here and you fixed it!! – Top-Bot Mar 22 at 15:29
5

The two solutions above were confusing for me.

You just need two blocks of modifications in /usr/lib/ssl/openssl.cnf as documented with this diff:

     rcsdiff ./openssl.cnf 
    ===================================================================
    RCS file: ./openssl.cnf,v
    retrieving revision 1.1
    diff -r1.1 ./openssl.cnf
    13a14,15
    > openssl_conf = default_conf
    > 
    350a353,362
    > 
    > [default_conf]
    > ssl_conf = ssl_sect
    > 
    > [ssl_sect]
    > system_default = system_default_sect
    > 
    > [system_default_sect]
    > MinProtocol = TLSv1.2
    > CipherString = DEFAULT@SECLEVEL=1

For cut&paste:

openssl_conf = default_conf
[default_conf]
ssl_conf = ssl_sect

[ssl_sect]
system_default = system_default_sect

[system_default_sect]
MinProtocol = TLSv1.2
CipherString = DEFAULT@SECLEVEL=1
1

Update: the previous answer seems to work if you extract the default configuration from the deb file by downloading it on https://packages.ubuntu.com/search?keywords=openssl&searchon=names.

Update 2: in fact the previous answer did not work for me because I had a wrong config file using [system_default_sect] instead of [ssl_default_sect]. It seems to be an error that I copy-pasted from https://wiki.debian.org/ContinuousIntegration/TriagingTips/openssl-1.1.1. It is possible to use the name system_default_sect to be consistent with Debian, you just need to use it everywhere instead of ssl_default_sect.

Original answer:

The previous answer was not working for me on Ubuntu 20.04 so I used the config file from my Debian LXC container on Ubuntu and changed SECLEVEL=2 to SECLEVEL=1.

I saved the file as /etc/ssl/openssl_custom.cnf and then used the command shared in the previous answer to load another config file when you need to:

export OPENSSL_CONF=/etc/ssl/openssl_custom.cnf

Here is the full config file that worked for me (you can also extract the default configuration from the deb file by downloading it on https://packages.debian.org/stable/openssl):

#
# OpenSSL example configuration file.
# This is mostly being used for generation of certificate requests.
#

# Note that you can include other files from the main configuration
# file using the .include directive.
#.include filename

# This definition stops the following lines choking if HOME isn't
# defined.
HOME                    = .

# Extra OBJECT IDENTIFIER info:
#oid_file               = $ENV::HOME/.oid
oid_section             = new_oids

# System default
openssl_conf = default_conf

# To use this configuration file with the "-extfile" option of the
# "openssl x509" utility, name here the section containing the
# X.509v3 extensions to use:
# extensions            =
# (Alternatively, use a configuration file that has only
# X.509v3 extensions in its main [= default] section.)

[ new_oids ]

# We can add new OIDs in here for use by 'ca', 'req' and 'ts'.
# Add a simple OID like this:
# testoid1=1.2.3.4
# Or use config file substitution like this:
# testoid2=${testoid1}.5.6

# Policies used by the TSA examples.
tsa_policy1 = 1.2.3.4.1
tsa_policy2 = 1.2.3.4.5.6
tsa_policy3 = 1.2.3.4.5.7

####################################################################
[ ca ]
default_ca      = CA_default            # The default ca section

####################################################################
[ CA_default ]

dir             = ./demoCA              # Where everything is kept
certs           = $dir/certs            # Where the issued certs are kept
crl_dir         = $dir/crl              # Where the issued crl are kept
database        = $dir/index.txt        # database index file.
#unique_subject = no                    # Set to 'no' to allow creation of
                                        # several certs with same subject.
new_certs_dir   = $dir/newcerts         # default place for new certs.

certificate     = $dir/cacert.pem       # The CA certificate
serial          = $dir/serial           # The current serial number
crlnumber       = $dir/crlnumber        # the current crl number
                                        # must be commented out to leave a V1 CRL
crl             = $dir/crl.pem          # The current CRL
private_key     = $dir/private/cakey.pem# The private key

x509_extensions = usr_cert              # The extensions to add to the cert

# Comment out the following two lines for the "traditional"
# (and highly broken) format.
name_opt        = ca_default            # Subject Name options
cert_opt        = ca_default            # Certificate field options

# Extension copying option: use with caution.
# copy_extensions = copy

# Extensions to add to a CRL. Note: Netscape communicator chokes on V2 CRLs
# so this is commented out by default to leave a V1 CRL.
# crlnumber must also be commented out to leave a V1 CRL.
# crl_extensions        = crl_ext

default_days    = 365                   # how long to certify for
default_crl_days= 30                    # how long before next CRL
default_md      = default               # use public key default MD
preserve        = no                    # keep passed DN ordering

# A few difference way of specifying how similar the request should look
# For type CA, the listed attributes must be the same, and the optional
# and supplied fields are just that :-)
policy          = policy_match

# For the CA policy
[ policy_match ]
countryName             = match
stateOrProvinceName     = match
organizationName        = match
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

# For the 'anything' policy
# At this point in time, you must list all acceptable 'object'
# types.
[ policy_anything ]
countryName             = optional
stateOrProvinceName     = optional
localityName            = optional
organizationName        = optional
organizationalUnitName  = optional
commonName              = supplied
emailAddress            = optional

####################################################################
[ req ]
default_bits            = 2048
default_keyfile         = privkey.pem
distinguished_name      = req_distinguished_name
attributes              = req_attributes
x509_extensions = v3_ca # The extensions to add to the self signed cert

# Passwords for private keys if not present they will be prompted for
# input_password = secret
# output_password = secret

# This sets a mask for permitted string types. There are several options.
# default: PrintableString, T61String, BMPString.
# pkix   : PrintableString, BMPString (PKIX recommendation before 2004)
# utf8only: only UTF8Strings (PKIX recommendation after 2004).
# nombstr : PrintableString, T61String (no BMPStrings or UTF8Strings).
# MASK:XXXX a literal mask value.
# WARNING: ancient versions of Netscape crash on BMPStrings or UTF8Strings.
string_mask = utf8only

# req_extensions = v3_req # The extensions to add to a certificate request

[ req_distinguished_name ]
countryName                     = Country Name (2 letter code)
countryName_default             = AU
countryName_min                 = 2
countryName_max                 = 2

stateOrProvinceName             = State or Province Name (full name)
stateOrProvinceName_default     = Some-State

localityName                    = Locality Name (eg, city)

0.organizationName              = Organization Name (eg, company)
0.organizationName_default      = Internet Widgits Pty Ltd

# we can do this but it is not needed normally :-)
#1.organizationName             = Second Organization Name (eg, company)
#1.organizationName_default     = World Wide Web Pty Ltd

organizationalUnitName          = Organizational Unit Name (eg, section)
#organizationalUnitName_default =

commonName                      = Common Name (e.g. server FQDN or YOUR name)
commonName_max                  = 64

emailAddress                    = Email Address
emailAddress_max                = 64

# SET-ex3                       = SET extension number 3

[ req_attributes ]
challengePassword               = A challenge password
challengePassword_min           = 4
challengePassword_max           = 20

unstructuredName                = An optional company name

[ usr_cert ]

# These extensions are added when 'ca' signs a request.

# This goes against PKIX guidelines but some CAs do it and some software
# requires this to avoid interpreting an end user certificate as a CA.

basicConstraints=CA:FALSE

# Here are some examples of the usage of nsCertType. If it is omitted
# the certificate can be used for anything *except* object signing.

# This is OK for an SSL server.
# nsCertType                    = server

# For an object signing certificate this would be used.
# nsCertType = objsign

# For normal client use this is typical
# nsCertType = client, email

# and for everything including object signing:
# nsCertType = client, email, objsign

# This is typical in keyUsage for a client certificate.
# keyUsage = nonRepudiation, digitalSignature, keyEncipherment

# This will be displayed in Netscape's comment listbox.
nsComment                       = "OpenSSL Generated Certificate"

# PKIX recommendations harmless if included in all certificates.
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid,issuer

# This stuff is for subjectAltName and issuerAltname.
# Import the email address.
# subjectAltName=email:copy
# An alternative to produce certificates that aren't
# deprecated according to PKIX.
# subjectAltName=email:move

# Copy subject details
# issuerAltName=issuer:copy

#nsCaRevocationUrl              = http://www.domain.dom/ca-crl.pem
#nsBaseUrl
#nsRevocationUrl
#nsRenewalUrl
#nsCaPolicyUrl
#nsSslServerName

# This is required for TSA certificates.
# extendedKeyUsage = critical,timeStamping

[ v3_req ]

# Extensions to add to a certificate request

basicConstraints = CA:FALSE
keyUsage = nonRepudiation, digitalSignature, keyEncipherment

[ v3_ca ]


# Extensions for a typical CA


# PKIX recommendation.

subjectKeyIdentifier=hash

authorityKeyIdentifier=keyid:always,issuer

basicConstraints = critical,CA:true

# Key usage: this is typical for a CA certificate. However since it will
# prevent it being used as an test self-signed certificate it is best
# left out by default.
# keyUsage = cRLSign, keyCertSign

# Some might want this also
# nsCertType = sslCA, emailCA

# Include email address in subject alt name: another PKIX recommendation
# subjectAltName=email:copy
# Copy issuer details
# issuerAltName=issuer:copy

# DER hex encoding of an extension: beware experts only!
# obj=DER:02:03
# Where 'obj' is a standard or added object
# You can even override a supported extension:
# basicConstraints= critical, DER:30:03:01:01:FF

[ crl_ext ]

# CRL extensions.
# Only issuerAltName and authorityKeyIdentifier make any sense in a CRL.

# issuerAltName=issuer:copy
authorityKeyIdentifier=keyid:always

[ proxy_cert_ext ]
# These extensions should be added when creating a proxy certificate

# This goes against PKIX guidelines but some CAs do it and some software
# requires this to avoid interpreting an end user certificate as a CA.

basicConstraints=CA:FALSE

# Here are some examples of the usage of nsCertType. If it is omitted
# the certificate can be used for anything *except* object signing.

# This is OK for an SSL server.
# nsCertType                    = server

# For an object signing certificate this would be used.
# nsCertType = objsign

# For normal client use this is typical
# nsCertType = client, email

# and for everything including object signing:
# nsCertType = client, email, objsign

# This is typical in keyUsage for a client certificate.
# keyUsage = nonRepudiation, digitalSignature, keyEncipherment

# This will be displayed in Netscape's comment listbox.
nsComment                       = "OpenSSL Generated Certificate"

# PKIX recommendations harmless if included in all certificates.
subjectKeyIdentifier=hash
authorityKeyIdentifier=keyid,issuer

# This stuff is for subjectAltName and issuerAltname.
# Import the email address.
# subjectAltName=email:copy
# An alternative to produce certificates that aren't
# deprecated according to PKIX.
# subjectAltName=email:move

# Copy subject details
# issuerAltName=issuer:copy

#nsCaRevocationUrl              = http://www.domain.dom/ca-crl.pem
#nsBaseUrl
#nsRevocationUrl
#nsRenewalUrl
#nsCaPolicyUrl
#nsSslServerName

# This really needs to be in place for it to be a proxy certificate.
proxyCertInfo=critical,language:id-ppl-anyLanguage,pathlen:3,policy:foo

####################################################################
[ tsa ]

default_tsa = tsa_config1       # the default TSA section

[ tsa_config1 ]

# These are used by the TSA reply generation only.
dir             = ./demoCA              # TSA root directory
serial          = $dir/tsaserial        # The current serial number (mandatory)
crypto_device   = builtin               # OpenSSL engine to use for signing
signer_cert     = $dir/tsacert.pem      # The TSA signing certificate
                                        # (optional)
certs           = $dir/cacert.pem       # Certificate chain to include in reply
                                        # (optional)
signer_key      = $dir/private/tsakey.pem # The TSA private key (optional)
signer_digest  = sha256                 # Signing digest to use. (Optional)
default_policy  = tsa_policy1           # Policy if request did not specify it
                                        # (optional)
other_policies  = tsa_policy2, tsa_policy3      # acceptable policies (optional)
digests     = sha1, sha256, sha384, sha512  # Acceptable message digests (mandatory)
accuracy        = secs:1, millisecs:500, microsecs:100  # (optional)
clock_precision_digits  = 0     # number of digits after dot. (optional)
ordering                = yes   # Is ordering defined for timestamps?
                                # (optional, default: no)
tsa_name                = yes   # Must the TSA name be included in the reply?
                                # (optional, default: no)
ess_cert_id_chain       = no    # Must the ESS cert id chain be included?
                                # (optional, default: no)
ess_cert_id_alg         = sha1  # algorithm to compute certificate
                                # identifier (optional, default: sha1)
[default_conf]
ssl_conf = ssl_sect

[ssl_sect]
system_default = system_default_sect

[system_default_sect]
MinProtocol = TLSv1.2
CipherString = DEFAULT@SECLEVEL=1

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