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[tls] Discard received Change Cipher records under TLS version 1.3

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TLS version 1.3 allows unencrypted Change Cipher records to be sent
after switching to use the handshake traffic keys.  This is an ugly
protocol hack to work around badly implemented firewalls of the kind
beloved by large organisations.

Ignore and discard any such records, which would otherwise cause
decryption failures.

Signed-off-by: Michael Brown <mcb30@ipxe.org>
This commit is contained in:
Michael Brown
2026-09-14 13:56:59 +01:00
parent 4ac73a5cbb
commit 6872d143d6
1 changed files with 23 additions and 4 deletions
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src/net/tls.c
+23 -4
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@@ -2308,9 +2308,10 @@ static int tls_new_change_cipher ( struct tls_connection *tls,
}
iob_pull ( iobuf, sizeof ( *change_cipher ) );
/* Change receive cipher spec */
if ( ( rc = tls_change_cipher ( tls, &tls->rx.cipherspec,
&tls_application ) ) != 0 ) {
/* Change receive cipher spec, if applicable */
if ( ( ! tls_version ( tls, TLS_VERSION_TLS_1_3 ) ) &&
( ( rc = tls_change_cipher ( tls, &tls->rx.cipherspec,
&tls_application ) ) != 0 ) ) {
return rc;
}
@@ -3716,6 +3717,7 @@ static int tls_new_ciphertext ( struct tls_connection *tls,
struct digest_algorithm *digest = suite->digest;
struct secure_pipe *pipe = &tls->channel.rx;
struct cipher_algorithm *cipher = pipe->cipher;
unsigned int type = tlshdr->type;
size_t len = ntohs ( tlshdr->length );
struct {
uint8_t fixed[suite->fixed_iv_len];
@@ -3736,6 +3738,23 @@ static int tls_new_ciphertext ( struct tls_connection *tls,
/* Sanity check */
assert ( cipher == suite->cipher );
/* Handle TLS version 1.3 Change Cipher records */
if ( tls_version ( tls, TLS_VERSION_TLS_1_3 ) &&
( type == TLS_TYPE_CHANGE_CIPHER ) ) {
/* TLS version 1.3 allows unencrypted Change Cipher
* records to be sent after switching to use the
* handshake traffic keys. This is an ugly protocol
* hack to work around badly implemented firewalls of
* the kind beloved by large organisations.
*
* Process these as plaintext records. Change Cipher
* records are ignored for TLS version 1.3, so this is
* just the most convenient way to discard the
* records.
*/
return tls_new_record ( tls, type, rx_data );
}
/* Locate first and last data buffers */
assert ( ! list_empty ( rx_data ) );
first = list_first_entry ( rx_data, struct io_buffer, list );
@@ -3856,7 +3875,7 @@ static int tls_new_ciphertext ( struct tls_connection *tls,
}
/* Process plaintext record */
if ( ( rc = tls_new_record ( tls, tlshdr->type, rx_data ) ) != 0 )
if ( ( rc = tls_new_record ( tls, type, rx_data ) ) != 0 )
return rc;
return 0;