Kafka TLS Doesn't Present Intermediary Certificates

[rrileyca]

Name and Version

bitnami/kafka:3.2.1-debian-11-r4

What steps will reproduce the bug?

We deploy this container from the Bitnami Kafka Helm Chart. When using PEM TLS certificates, Kafka does not present the entire certificate chain.

Our /opt/bitnami/kafka/config/server.properties file looks like this:

ssl.keystore.type=PEM
ssl.truststore.type=PEM
ssl.keystore.key=-----BEGIN PRIVATE KEY----- \
<redacted>
-----END PRIVATE KEY-----
ssl.keystore.certificate.chain=-----BEGIN CERTIFICATE----- \
<redacted>
-----END CERTIFICATE----- \
-----BEGIN CERTIFICATE----- \
MIIFFjCCAv6gAwIBAgIRAJErCErPDBinU/bWLiWnX1owDQYJKoZIhvcNAQELBQAw \
TzELMAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2Vh \
cmNoIEdyb3VwMRUwEwYDVQQDEwxJU1JHIFJvb3QgWDEwHhcNMjAwOTA0MDAwMDAw \
WhcNMjUwOTE1MTYwMDAwWjAyMQswCQYDVQQGEwJVUzEWMBQGA1UEChMNTGV0J3Mg \
RW5jcnlwdDELMAkGA1UEAxMCUjMwggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEK \
AoIBAQC7AhUozPaglNMPEuyNVZLD+ILxmaZ6QoinXSaqtSu5xUyxr45r+XXIo9cP \
R5QUVTVXjJ6oojkZ9YI8QqlObvU7wy7bjcCwXPNZOOftz2nwWgsbvsCUJCWH+jdx \
sxPnHKzhm+/b5DtFUkWWqcFTzjTIUu61ru2P3mBw4qVUq7ZtDpelQDRrK9O8Zutm \
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Z3Vms/EY96Jc5lP/Ooi2R6X/ExjqmAl3P51T+c8B5fWmcBcUr2Ok/5mzk53cU6cG \
/kiFHaFpriV1uxPMUgP17VGhi9sVAgMBAAGjggEIMIIBBDAOBgNVHQ8BAf8EBAMC \
AYYwHQYDVR0lBBYwFAYIKwYBBQUHAwIGCCsGAQUFBwMBMBIGA1UdEwEB/wQIMAYB \
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lJNXoB1lBMEKIq4QDUOXoRgffuDghje1WrG9ML+Hbisq/yFOGwXD9RiX8F6sw6W4 \
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yJMC6alLbBfODALZvYH7n7do1AZls4I9d1P4jnkDrQoxB3UqQ9hVl3LEKQ73xF1O \
yK5GhDDX8oVfGKF5u+decIsH4YaTw7mP3GFxJSqv3+0lUFJoi5Lc5da149p90Ids \
hCExroL1+7mryIkXPeFM5TgO9r0rvZaBFOvV2z0gp35Z0+L4WPlbuEjN/lxPFin+ \
HlUjr8gRsI3qfJOQFy/9rKIJR0Y/8Omwt/8oTWgy1mdeHmmjk7j1nYsvC9JSQ6Zv \
MldlTTKB3zhThV1+XWYp6rjd5JW1zbVWEkLNxE7GJThEUG3szgBVGP7pSWTUTsqX \
nLRbwHOoq7hHwg== \
-----END CERTIFICATE----- \
ssl.truststore.certificates=-----BEGIN CERTIFICATE----- \
MIIFazCCA1OgAwIBAgIRAIIQz7DSQONZRGPgu2OCiwAwDQYJKoZIhvcNAQELBQAw \
TzELMAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2Vh \
cmNoIEdyb3VwMRUwEwYDVQQDEwxJU1JHIFJvb3QgWDEwHhcNMTUwNjA0MTEwNDM4 \
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mRGunUHBcnWEvgJBQl9nJEiU0Zsnvgc/ubhPgXRR4Xq37Z0j4r7g1SgEEzwxA57d \
emyPxgcYxn/eR44/KJ4EBs+lVDR3veyJm+kXQ99b21/+jh5Xos1AnX5iItreGCc= \
-----END CERTIFICATE-----

The ssl.keystore.certificate.chain has (in order) our endpoint certificate followed by the Let's Encrypt R3 Intermediate certificate underneath it. The ssl.truststore.certificates entry is the Let's Encrypt ISRG Root X1 CA certificate.

We can test the configuration with:

openssl s_client -connect myhost.mydomain.com -port 9094

Which returns the below output. The output says that only one certificate is being presented, and it is the Intermediate certificate and not the endpoint/leaf certificate, which is why the signature is failing.

CONNECTED(00000003)
depth=1 C = US, O = Internet Security Research Group, CN = ISRG Root X1
verify return:1
depth=0 C = US, O = Let's Encrypt, CN = R3
verify return:1
140176629757248:error:0407E086:rsa routines:RSA_verify_PKCS1_PSS_mgf1:last octet invalid:../crypto/rsa/rsa_pss.c:88:
140176629757248:error:1417B07B:SSL routines:tls_process_cert_verify:bad signature:../ssl/statem/statem_lib.c:504:
---
Certificate chain
 0 s:C = US, O = Let's Encrypt, CN = R3
   i:C = US, O = Internet Security Research Group, CN = ISRG Root X1
---
Server certificate
-----BEGIN CERTIFICATE-----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hCExroL1+7mryIkXPeFM5TgO9r0rvZaBFOvV2z0gp35Z0+L4WPlbuEjN/lxPFin+
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MldlTTKB3zhThV1+XWYp6rjd5JW1zbVWEkLNxE7GJThEUG3szgBVGP7pSWTUTsqX
nLRbwHOoq7hHwg==
-----END CERTIFICATE-----
subject=C = US, O = Let's Encrypt, CN = R3

issuer=C = US, O = Internet Security Research Group, CN = ISRG Root X1

---
No client certificate CA names sent
Peer signing digest: SHA256
Peer signature type: RSA-PSS
Server Temp Key: X25519, 253 bits
---
SSL handshake has read 1838 bytes and written 329 bytes
Verification: OK
---
New, TLSv1.3, Cipher is TLS_AES_256_GCM_SHA384
Server public key is 2048 bit
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
Early data was not sent
Verify return code: 0 (ok)
---

If I remove the Intermediary certificate from the ssl.keystore.certificate.chain entry, Kafka now sends me the endpoint certificate but without the Intermediary certificate. This means the certificate will not be trusted unless the intermediary certificate is manually trusted. The output of openssl s_client -connect myhost.mydomain.com -port 9094 is now:

CONNECTED(00000003)
depth=0 CN = myhost.mydomain.com
verify error:num=20:unable to get local issuer certificate
verify return:1
depth=0 CN = myhost.mydomain.com
verify error:num=21:unable to verify the first certificate
verify return:1
---
Certificate chain
 0 s:CN = myhost.mydomain.com
   i:C = US, O = Let's Encrypt, CN = R3
---
Server certificate
-----BEGIN CERTIFICATE-----
<redacted>
-----END CERTIFICATE-----
subject=CN = myhost.mydomain.com

issuer=C = US, O = Let's Encrypt, CN = R3

---
No client certificate CA names sent
Peer signing digest: SHA256
Peer signature type: RSA-PSS
Server Temp Key: X25519, 253 bits
---
SSL handshake has read 2011 bytes and written 402 bytes
Verification error: unable to verify the first certificate
---
New, TLSv1.3, Cipher is TLS_AES_256_GCM_SHA384
Server public key is 2048 bit
Secure Renegotiation IS NOT supported
Compression: NONE
Expansion: NONE
No ALPN negotiated
Early data was not sent
Verify return code: 21 (unable to verify the first certificate)
---
---
Post-Handshake New Session Ticket arrived:
SSL-Session:
    Protocol  : TLSv1.3
    Cipher    : TLS_AES_256_GCM_SHA384
    Session-ID: <redacted>
    Session-ID-ctx:
    Resumption PSK: <redacted>
    PSK identity: None
    PSK identity hint: None
    SRP username: None
    TLS session ticket lifetime hint: 86400 (seconds)
    TLS session ticket:
    <redacted>

    Start Time: 1663274615
    Timeout   : 7200 (sec)
    Verify return code: 21 (unable to verify the first certificate)
    Extended master secret: no
    Max Early Data: 0

The current workaround is to install the Intermediary certificate in the root of trust.

I have tried reversing the order of the certificates in the ssl.keystore.certificate.chain entry, which makes Kafka throw errors (as expected).

I have also tried adding the Root certificate to the ssl.keystore.certificate.chain (a total of 3 certificates), and this results in the Root CA certificate alone being sent in the TLS handshake. It seems that Kafka always sends a single certificate, and it is always the last one in the ssl.keystore.certificate.chain chain.

What is the expected behavior?

Kafka TLS should send the endpoint certificate along with all intermediary CA's in the TLS handshake.

What do you see instead?

Only a single certificate is sent when a chain is provided.

Additional information

No response

[rafariossaa]

Hi @rrileyca ,
If kafka is not behaving as expected, and the config file is correctly generated, I think you should report this issue directly to kafka team.

[rrileyca]

Done. Link for future visibility: https://issues.apache.org/jira/browse/KAFKA-14237

[rafariossaa]

Thanks @rrileyca .
Please, don't hesitate to come back.

[github-actions]

This Issue has been automatically marked as "stale" because it has not had recent activity (for 15 days). It will be closed if no further activity occurs. Thanks for the feedback.

[github-actions]

Due to the lack of activity in the last 5 days since it was marked as "stale", we proceed to close this Issue. Do not hesitate to reopen it later if necessary.