Code: iakerb_gss_accept_sec_context(OM_uint32 *minor_status,
                              gss_ctx_id_t *context_handle,
                              gss_cred_id_t verifier_cred_handle,
                              gss_buffer_t input_token,
                              gss_channel_bindings_t input_chan_bindings,
                              gss_name_t *src_name,
                              gss_OID *mech_type,
                              gss_buffer_t output_token,
                              OM_uint32 *ret_flags,
                              OM_uint32 *time_rec,
                              gss_cred_id_t *delegated_cred_handle)
{
    OM_uint32 major_status = GSS_S_FAILURE;
    OM_uint32 code;
    iakerb_ctx_id_t ctx;
     int initialContextToken = (*context_handle == GSS_C_NO_CONTEXT);
 
     if (initialContextToken) {
        code = iakerb_alloc_context(&ctx);
         if (code != 0)
             goto cleanup;
 
    } else
        ctx = (iakerb_ctx_id_t)*context_handle;

    if (iakerb_is_iakerb_token(input_token)) {
        if (ctx->gssc != GSS_C_NO_CONTEXT) {
            /* We shouldn't get an IAKERB token now. */
            code = G_WRONG_TOKID;
            major_status = GSS_S_DEFECTIVE_TOKEN;
            goto cleanup;
        }
        code = iakerb_acceptor_step(ctx, initialContextToken,
                                    input_token, output_token);
        if (code == (OM_uint32)KRB5_BAD_MSIZE)
            major_status = GSS_S_DEFECTIVE_TOKEN;
        if (code != 0)
            goto cleanup;
        if (initialContextToken) {
            *context_handle = (gss_ctx_id_t)ctx;
            ctx = NULL;
        }
        if (src_name != NULL)
            *src_name = GSS_C_NO_NAME;
        if (mech_type != NULL)
            *mech_type = (gss_OID)gss_mech_iakerb;
        if (ret_flags != NULL)
            *ret_flags = 0;
        if (time_rec != NULL)
            *time_rec = 0;
        if (delegated_cred_handle != NULL)
            *delegated_cred_handle = GSS_C_NO_CREDENTIAL;
        major_status = GSS_S_CONTINUE_NEEDED;
    } else {
        krb5_gss_ctx_ext_rec exts;

        iakerb_make_exts(ctx, &exts);

        major_status = krb5_gss_accept_sec_context_ext(&code,
                                                       &ctx->gssc,
                                                       verifier_cred_handle,
                                                       input_token,
                                                       input_chan_bindings,
                                                       src_name,
                                                       NULL,
                                                       output_token,
                                                       ret_flags,
                                                        time_rec,
                                                        delegated_cred_handle,
                                                        &exts);
        if (major_status == GSS_S_COMPLETE) {
            *context_handle = ctx->gssc;
            ctx->gssc = NULL;
            iakerb_release_context(ctx);
        }
         if (mech_type != NULL)
             *mech_type = (gss_OID)gss_mech_krb5;
     }

cleanup:
    if (initialContextToken && GSS_ERROR(major_status)) {
        iakerb_release_context(ctx);
        *context_handle = GSS_C_NO_CONTEXT;
    }

    *minor_status = code;
    return major_status;
}

Vulnerability Type: DoS 
CWE ID: CWE-18
Summary: lib/gssapi/krb5/iakerb.c in MIT Kerberos 5 (aka krb5) before 1.14 relies on an inappropriate context handle, which allows remote attackers to cause a denial of service (incorrect pointer read and process crash) via a crafted IAKERB packet that is mishandled during a gss_inquire_context call.
Commit Message: Fix IAKERB context aliasing bugs [CVE-2015-2696]

The IAKERB mechanism currently replaces its context handle with the
krb5 mechanism handle upon establishment, under the assumption that
most GSS functions are only called after context establishment.  This
assumption is incorrect, and can lead to aliasing violations for some
programs.  Maintain the IAKERB context structure after context
establishment and add new IAKERB entry points to refer to it with that
type.  Add initiate and established flags to the IAKERB context
structure for use in gss_inquire_context() prior to context
establishment.

CVE-2015-2696:

In MIT krb5 1.9 and later, applications which call
gss_inquire_context() on a partially-established IAKERB context can
cause the GSS-API library to read from a pointer using the wrong type,
generally causing a process crash.  Java server applications using the
native JGSS provider are vulnerable to this bug.  A carefully crafted
IAKERB packet might allow the gss_inquire_context() call to succeed
with attacker-determined results, but applications should not make
access control decisions based on gss_inquire_context() results prior
to context establishment.

    CVSSv2 Vector: AV:N/AC:M/Au:N/C:N/I:N/A:C/E:POC/RL:OF/RC:C

[ghudson@mit.edu: several bugfixes, style changes, and edge-case
behavior changes; commit message and CVE description]

ticket: 8244
target_version: 1.14
tags: pullup