CVE-2014-4343 (published 2014-08-14T05:01Z)

Double free vulnerability in the init_ctx_reselect function in the SPNEGO initiator in lib/gssapi/spnego/spnego_mech.c in MIT Kerberos 5 (aka krb5) 1.10.x through 1.12.x before 1.12.2 allows remote attackers to cause a denial of service (memory corruption) or possibly execute arbitrary code via network traffic that appears to come from an intended acceptor, but specifies a security mechanism different from the one proposed by the initiator.

Severity: HIGH
CVSS v2 base score: 7.6 (AV:N/AC:H/Au:N/C:C/I:C/A:C)

Weakness information:
cwe_id: CWE-415
cwe_name: Double Free
description: The product calls free() twice on the same memory address, potentially leading to modification of unexpected memory locations.
extended_description: When a program calls free() twice with the same argument, the program's memory management data structures become corrupted. This corruption can cause the program to crash or, in some circumstances, cause two later calls to malloc() to return the same pointer. If malloc() returns the same value twice and the program later gives the attacker control over the data that is written into this doubly-allocated memory, the program becomes vulnerable to a buffer overflow attack.
         

Fix information:
repo_url: https://github.com/krb5/krb5
commit_details: repo_url: https://github.com/krb5/krb5
author: David Woodhouse
author_date: 2014-07-15 12:54:15-04:00
msg: Fix double-free in SPNEGO [CVE-2014-4343]

In commit cd7d6b08 ("Verify acceptor's mech in SPNEGO initiator") the
pointer sc->internal_mech became an alias into sc->mech_set->elements,
which should be considered constant for the duration of the SPNEGO
context.  So don't free it.

CVE-2014-4343:

In MIT krb5 releases 1.10 and newer, an unauthenticated remote
attacker with the ability to spoof packets appearing to be from a
GSSAPI acceptor can cause a double-free condition in GSSAPI initiators
(clients) which are using the SPNEGO mechanism, by returning a
different underlying mechanism than was proposed by the initiator.  At
this stage of the negotiation, the acceptor is unauthenticated, and
the acceptor's response could be spoofed by an attacker with the
ability to inject traffic to the initiator.

Historically, some double-free vulnerabilities can be translated into
remote code execution, though the necessary exploits must be tailored
to the individual application and are usually quite
complicated. Double-frees can also be exploited to cause an
application crash, for a denial of service.  However, most GSSAPI
client applications are not vulnerable, as the SPNEGO mechanism is not
used by default (when GSS_C_NO_OID is passed as the mech_type argument
to gss_init_sec_context()).  The most common use of SPNEGO is for
HTTP-Negotiate, used in web browsers and other web clients.  Most such
clients are believed to not offer HTTP-Negotiate by default, instead
requiring a whitelist of sites for which it may be used to be
configured.  If the whitelist is configured to only allow
HTTP-Negotiate over TLS connections ("https://"), a successful
attacker must also spoof the web server's SSL certificate, due to the
way the WWW-Authenticate header is sent in a 401 (Unauthorized)
response message.  Unfortunately, many instructions for enabling
HTTP-Negotiate in common web browsers do not include a TLS
requirement.

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

[kaduk@mit.edu: CVE summary and CVSSv2 vector]

ticket: 7969 (new)
target_version: 1.12.2
tags: pullup
repository: repo_url: https://github.com/krb5/krb5
repo_name: krb5/krb5
description: mirror of MIT krb5 repository
repo_language: C
owner: krb5
file_changes: filename: spnego_mech.c
change_type: ModificationType.MODIFY
diff: @@ -818,7 +818,6 @@ init_ctx_reselect(OM_uint32 *minor_status, spnego_gss_ctx_id_t sc,
 	OM_uint32 tmpmin;
 	size_t i;
 
-	generic_gss_release_oid(&tmpmin, &sc->internal_mech);
 	gss_delete_sec_context(&tmpmin, &sc->ctx_handle,
 			       GSS_C_NO_BUFFER);
 

programming_language: C