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BUG/MINOR: ssl: suboptimal certificate selection with TLSv1.3 and dual ECDSA/RSA

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When using TLSv1.3, the signature algorithms extension is used to chose
the right ECDSA or RSA certificate.

However there was an old test for previous version of TLS (< 1.3) which
was testing if the cipher is compatible with ECDSA when an ECDSA
signature algorithm is used. This test was relying on
SSL_CIPHER_get_auth_nid(cipher) == NID_auth_ecdsa to verify if the
cipher is still good.

Problem is, with TLSv1.3, all ciphersuites are compatible with any
authentication algorithm, but SSL_CIPHER_get_auth_nid(cipher) does not
return NID_auth_ecdsa, but NID_auth_any.

Because of this, with TLSv1.3 when both ECDSA and RSA certificates are
available for a domain, the ECDSA one is not chosen in priority.

This patch also introduces a test on the cipher IDs for the signaling
ciphersuites, because they would always return NID_auth_any, and are not
relevent for this selection.

This patch fixes issue #2300.

Must be backported in all stable versions.
This commit is contained in:
William Lallemand 2023-10-24 23:58:02 +02:00
parent 4a89dba6d5
commit 23093c72f1
1 changed files with 8 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
src/ssl_sock.c
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@ -2487,6 +2487,7 @@ int ssl_sock_switchctx_cbk(SSL *ssl, int *al, void *arg)
} }
if (has_ecdsa_sig) { /* in very rare case: has ecdsa sign but not a ECDSA cipher */ if (has_ecdsa_sig) { /* in very rare case: has ecdsa sign but not a ECDSA cipher */
const SSL_CIPHER *cipher; const SSL_CIPHER *cipher;
uint32_t cipher_id;
size_t len; size_t len;
const uint8_t *cipher_suites; const uint8_t *cipher_suites;
has_ecdsa_sig = 0; has_ecdsa_sig = 0;
@ -2505,7 +2506,13 @@ int ssl_sock_switchctx_cbk(SSL *ssl, int *al, void *arg)
#else #else
cipher = SSL_CIPHER_find(ssl, cipher_suites); cipher = SSL_CIPHER_find(ssl, cipher_suites);
#endif #endif
if (cipher && SSL_CIPHER_get_auth_nid(cipher) == NID_auth_ecdsa) { cipher_id = SSL_CIPHER_get_id(cipher);
/* skip the SCSV "fake" signaling ciphersuites because they are NID_auth_any (RFC 7507) */
if (cipher_id == SSL3_CK_SCSV || cipher_id == SSL3_CK_FALLBACK_SCSV)
continue;
if (cipher && ( SSL_CIPHER_get_auth_nid(cipher) == NID_auth_ecdsa
|| SSL_CIPHER_get_auth_nid(cipher) == NID_auth_any)) {
has_ecdsa_sig = 1; has_ecdsa_sig = 1;
break; break;
} }