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eap-authenticator: Enforce failure if MSK generation fails

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Without this, the authentication succeeded if the server sent an early
EAP-Success message for mutual, key-generating EAP methods like EAP-TLS,
which may be used in EAP-only scenarios but would complete without server
or client authentication.  For clients configured for such EAP-only
scenarios, a rogue server could capture traffic after the tunnel is
established or even access hosts behind the client.  For non-mutual EAP
methods, public key server authentication has been enforced for a while.

A server previously could also crash a client by sending an EAP-Success
immediately without initiating an actual EAP method.

Fixes: 0706c39cda52 ("added support for EAP methods not establishing an MSK")
Fixes: CVE-2021-45079
This commit is contained in:
Tobias Brunner 2021-12-14 10:51:35 +01:00
parent de15386d94
commit 64cc9acbf0
5 changed files with 40 additions and 8 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
src/libcharon/plugins/eap_gtc/eap_gtc.c
View File

@ -195,7 +195,7 @@ METHOD(eap_method_t, get_type, eap_type_t,
METHOD(eap_method_t, get_msk, status_t,
private_eap_gtc_t *this, chunk_t *msk)
{
return FAILED;
return NOT_SUPPORTED;
}
METHOD(eap_method_t, get_identifier, uint8_t,

2
src/libcharon/plugins/eap_md5/eap_md5.c
View File

@ -213,7 +213,7 @@ METHOD(eap_method_t, get_type, eap_type_t,
METHOD(eap_method_t, get_msk, status_t,
private_eap_md5_t *this, chunk_t *msk)
{
return FAILED;
return NOT_SUPPORTED;
}
METHOD(eap_method_t, is_mutual, bool,

4
src/libcharon/plugins/eap_radius/eap_radius.c
View File

@ -733,7 +733,9 @@ METHOD(eap_method_t, get_msk, status_t,
*out = msk;
return SUCCESS;
}
return FAILED;
/* we assume the selected method did not establish an MSK, if it failed
* to establish one, process() would have failed */
return NOT_SUPPORTED;
}
METHOD(eap_method_t, get_identifier, uint8_t,

8
src/libcharon/sa/eap/eap_method.h
View File

@ -114,10 +114,16 @@ struct eap_method_t {
* Not all EAP methods establish a shared secret. For implementations of
* the EAP-Identity method, get_msk() returns the received identity.
*
* @note Returning NOT_SUPPORTED is important for implementations of EAP
* methods that don't establish an MSK. In particular as client because
* key-generating EAP methods MUST fail to process EAP-Success messages if
* no MSK is established.
*
* @param msk chunk receiving internal stored MSK
* @return
* - SUCCESS, or
* - SUCCESS, if MSK is established
* - FAILED, if MSK not established (yet)
* - NOT_SUPPORTED, for non-MSK-establishing methods
*/
status_t (*get_msk) (eap_method_t *this, chunk_t *msk);

32
src/libcharon/sa/ikev2/authenticators/eap_authenticator.c
View File

@ -305,9 +305,17 @@ static eap_payload_t* server_process_eap(private_eap_authenticator_t *this,
this->method->destroy(this->method);
return server_initiate_eap(this, FALSE);
}
if (this->method->get_msk(this->method, &this->msk) == SUCCESS)
switch (this->method->get_msk(this->method, &this->msk))
{
this->msk = chunk_clone(this->msk);
case SUCCESS:
this->msk = chunk_clone(this->msk);
break;
case NOT_SUPPORTED:
break;
case FAILED:
default:
DBG1(DBG_IKE, "failed to establish MSK");
goto failure;
}
if (vendor)
{
@ -326,6 +334,7 @@ static eap_payload_t* server_process_eap(private_eap_authenticator_t *this,
return eap_payload_create_code(EAP_SUCCESS, in->get_identifier(in));
case FAILED:
default:
failure:
/* type might have changed for virtual methods */
type = this->method->get_type(this->method, &vendor);
if (vendor)
@ -661,9 +670,24 @@ METHOD(authenticator_t, process_client, status_t,
uint32_t vendor;
auth_cfg_t *cfg;
if (this->method->get_msk(this->method, &this->msk) == SUCCESS)
if (!this->method)
{
this->msk = chunk_clone(this->msk);
DBG1(DBG_IKE, "received unexpected %N",
eap_code_names, eap_payload->get_code(eap_payload));
return FAILED;
}
switch (this->method->get_msk(this->method, &this->msk))
{
case SUCCESS:
this->msk = chunk_clone(this->msk);
break;
case NOT_SUPPORTED:
break;
case FAILED:
default:
DBG1(DBG_IKE, "received %N but failed to establish MSK",
eap_code_names, eap_payload->get_code(eap_payload));
return FAILED;
}
type = this->method->get_type(this->method, &vendor);
if (vendor)