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Merge 59b0cf185ea13e9f79c0978ebe4d6f67567467f6 into f4a1aceb8ca7198b11447d6e1885ce70feb2dcc6

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Frank Mertens 2026-07-27 21:02:43 +01:00 committed by GitHub
commit d2d513c3df
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5 changed files with 40 additions and 20 deletions
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6
ChangeLog.d/fix-psk-identity-hint-empty.txt Normal file
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@ -0,0 +1,6 @@
Bugfix
* Make the TLS 1.2 server to not reject a Client Key Exchange message which
has a zero-length PSK identity hint (as allowed by RFC 4279). TLS clients
usually pass an empty PSK identity hint when the server accepts only a
single pre-shared key. This fix only affects TLS 1.2 servers using PSK
based ciphersuites.

35
include/mbedtls/ssl.h
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@ -3864,11 +3864,21 @@ int mbedtls_ssl_set_hs_psk_opaque(mbedtls_ssl_context *ssl,
/**
* \brief Set the PSK callback (server-side only).
*
* If set, the PSK callback is called for each
* handshake where a PSK-based ciphersuite was negotiated.
* The caller provides the identity received and wants to
* receive the actual PSK data and length.
* If set, the PSK callback is called for each
* handshake where a PSK-based ciphersuite was negotiated.
* The caller provides the identity received and wants to
* receive the actual PSK data and length.
*
* If a valid PSK identity is found, the callback should use
* \c mbedtls_ssl_set_hs_psk() or
* \c mbedtls_ssl_set_hs_psk_opaque()
* on the SSL context to set the correct PSK and return \c 0.
* Any other return value will result in a denied PSK identity.
*
* \param conf The SSL configuration to register the callback with.
*
* \param f_psk The callback for selecting and setting the PSK based
* in the PSK identity chosen by the client.
* The callback has the following parameters:
* - \c void*: The opaque pointer \p p_psk.
* - \c mbedtls_ssl_context*: The SSL context to which
@ -3878,11 +3888,8 @@ int mbedtls_ssl_set_hs_psk_opaque(mbedtls_ssl_context *ssl,
* - \c size_t: The length of the PSK identity
* selected by the client.
*
* If a valid PSK identity is found, the callback should use
* \c mbedtls_ssl_set_hs_psk() or
* \c mbedtls_ssl_set_hs_psk_opaque()
* on the SSL context to set the correct PSK and return \c 0.
* Any other return value will result in a denied PSK identity.
* \param p_psk A pointer to an opaque structure to be passed to
* the callback, for example a PSK store.
*
* \note A dynamic PSK (i.e. set by the PSK callback) takes
* precedence over a static PSK (i.e. set by
@ -3893,11 +3900,11 @@ int mbedtls_ssl_set_hs_psk_opaque(mbedtls_ssl_context *ssl,
* \c mbedtls_ssl_conf_psk() or
* \c mbedtls_ssl_conf_psk_opaque()).
*
* \param conf The SSL configuration to register the callback with.
* \param f_psk The callback for selecting and setting the PSK based
* in the PSK identity chosen by the client.
* \param p_psk A pointer to an opaque structure to be passed to
* the callback, for example a PSK store.
* \warning If an empty PSK key identity is provided by the client the
* \p f_psk callback is invoked with the length parameter set
* to zero. It is up to the server to set the default PSK or to
* reject the request in this case.
*
*/
void mbedtls_ssl_conf_psk_cb(mbedtls_ssl_config *conf,
int (*f_psk)(void *, mbedtls_ssl_context *, const unsigned char *,

9
library/ssl_tls.c
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@ -2175,14 +2175,16 @@ static int ssl_conf_set_psk_identity(mbedtls_ssl_config *conf,
size_t psk_identity_len)
{
/* Identity len will be encoded on two bytes */
if (psk_identity == NULL ||
psk_identity_len == 0 ||
if (psk_identity == NULL ||
(psk_identity_len >> 16) != 0 ||
psk_identity_len > MBEDTLS_SSL_OUT_CONTENT_LEN) {
return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
}
conf->psk_identity = mbedtls_calloc(1, psk_identity_len);
if (conf->psk_identity == NULL && psk_identity_len == 0) {
conf->psk_identity = mbedtls_calloc(1, 1);
}
if (conf->psk_identity == NULL) {
return MBEDTLS_ERR_SSL_ALLOC_FAILED;
}
@ -2208,9 +2210,6 @@ int mbedtls_ssl_conf_psk(mbedtls_ssl_config *conf,
if (psk == NULL) {
return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
}
if (psk_len == 0) {
return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
}
if (psk_len > MBEDTLS_PSK_MAX_LEN) {
return MBEDTLS_ERR_SSL_BAD_INPUT_DATA;
}

2
library/ssl_tls12_server.c
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@ -3502,7 +3502,7 @@ static int ssl_parse_client_psk_identity(mbedtls_ssl_context *ssl, unsigned char
n = MBEDTLS_GET_UINT16_BE(*p, 0);
*p += 2;
if (n == 0 || n > end - *p) {
if (n > end - *p) {
MBEDTLS_SSL_DEBUG_MSG(1, ("bad client key exchange message"));
return MBEDTLS_ERR_SSL_DECODE_ERROR;
}

8
tests/ssl-opt.sh
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@ -9672,6 +9672,14 @@ run_test "PSK callback: wrong key" \
-S "SSL - Unknown identity received" \
-s "SSL - Verification of the message MAC failed"
requires_config_enabled MBEDTLS_SSL_PROTO_TLS1_2
run_test "PSK callback: empty identity hint" \
"$P_SRV psk=73776f726466697368 psk_identity=''" \
"$P_CLI psk=73776f726466697368 force_version=tls12 psk_identity=''" \
0 \
-s "Successful connection" \
-c "Successful connection"
# Tests for EC J-PAKE
requires_config_enabled MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED