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schannel: fix user-set legacy algorithms in Windows 10 & 11

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- If the user set a legacy algorithm list (CURLOPT_SSL_CIPHER_LIST) then
  use the SCHANNEL_CRED legacy structure to pass the list to Schannel.

- If the user set both a legacy algorithm list and a TLS 1.3 cipher list
  then abort.

Although MS doesn't document it, Schannel will not negotiate TLS 1.3
when SCHANNEL_CRED is used. That means setting a legacy algorithm list
limits the user to earlier versions of TLS.

Prior to this change, since 8beff435 (precedes 7.85.0), libcurl would
ignore legacy algorithms in Windows 10 1809 and later.

Reported-by: zhihaoy@users.noreply.github.com

Fixes https://github.com/curl/curl/pull/10741
Closes https://github.com/curl/curl/pull/10746
This commit is contained in:
Jay Satiro 2023-03-19 04:05:08 -04:00
parent 4169943d15
commit b4f9ae5126
5 changed files with 45 additions and 13 deletions
Download patch file Download diff file Expand all files Collapse all files

30
lib/vtls/schannel.c
View file

@ -793,8 +793,11 @@ schannel_acquire_credential_handle(struct Curl_cfilter *cf,
backend->cred->client_cert_store = client_cert_store;
#endif
/* Windows 10, 1809 (a.k.a. Windows 10 build 17763) */
if(curlx_verify_windows_version(10, 0, 17763, PLATFORM_WINNT,
/* We support TLS 1.3 starting in Windows 10 version 1809 (OS build 17763) as
long as the user did not set a legacy algorithm list
(CURLOPT_SSL_CIPHER_LIST). */
if(!conn_config->cipher_list &&
curlx_verify_windows_version(10, 0, 17763, PLATFORM_WINNT,
VERSION_GREATER_THAN_EQUAL)) {
char *ciphers13 = 0;
@ -844,7 +847,7 @@ schannel_acquire_credential_handle(struct Curl_cfilter *cf,
/* reject too-long cipher names */
if(n > (LONGEST_ALG_ID - 1)) {
failf(data, "Cipher name too long, not checked.");
failf(data, "schannel: Cipher name too long, not checked");
return CURLE_SSL_CIPHER;
}
@ -872,7 +875,7 @@ schannel_acquire_credential_handle(struct Curl_cfilter *cf,
disable_aes_ccm_sha256 = FALSE;
}
else {
failf(data, "Passed in an unknown TLS 1.3 cipher.");
failf(data, "schannel: Unknown TLS 1.3 cipher: %s", tmp);
return CURLE_SSL_CIPHER;
}
@ -887,7 +890,7 @@ schannel_acquire_credential_handle(struct Curl_cfilter *cf,
if(disable_aes_gcm_sha384 && disable_aes_gcm_sha256
&& disable_chacha_poly && disable_aes_ccm_8_sha256
&& disable_aes_ccm_sha256) {
failf(data, "All available TLS 1.3 ciphers were disabled.");
failf(data, "schannel: All available TLS 1.3 ciphers were disabled");
return CURLE_SSL_CIPHER;
}
@ -1010,7 +1013,9 @@ schannel_acquire_credential_handle(struct Curl_cfilter *cf,
&backend->cred->time_stamp);
}
else {
/* Pre-Windows 10 1809 */
/* Pre-Windows 10 1809 or the user set a legacy algorithm list. Although MS
doesn't document it, currently Schannel will not negotiate TLS 1.3 when
SCHANNEL_CRED is used. */
ALG_ID algIds[NUM_CIPHERS];
char *ciphers = conn_config->cipher_list;
SCHANNEL_CRED schannel_cred = { 0 };
@ -1019,9 +1024,20 @@ schannel_acquire_credential_handle(struct Curl_cfilter *cf,
schannel_cred.grbitEnabledProtocols = enabled_protocols;
if(ciphers) {
if((enabled_protocols & SP_PROT_TLS1_3_CLIENT)) {
infof(data, "schannel: WARNING: This version of Schannel may "
"negotiate a less-secure TLS version than TLS 1.3 because the "
"user set an algorithm cipher list.");
}
if(conn_config->cipher_list13) {
failf(data, "schannel: This version of Schannel does not support "
"setting an algorithm cipher list and TLS 1.3 cipher list at "
"the same time");
return CURLE_SSL_CIPHER;
}
result = set_ssl_ciphers(&schannel_cred, ciphers, algIds);
if(CURLE_OK != result) {
failf(data, "Unable to set ciphers to from connection ssl config");
failf(data, "schannel: Failed setting algorithm cipher list");
return result;
}
}