[28825] in CVS-changelog-for-Kerberos-V5
krb5 commit [krb5-1.13]: Fix krb5_read_message handling
daemon@ATHENA.MIT.EDU (Tom Yu)
Mon Mar 2 17:32:56 2015
Date: Mon, 2 Mar 2015 17:32:50 -0500
From: Tom Yu <tlyu@mit.edu>
Message-Id: <201503022232.t22MWoj6015850@drugstore.mit.edu>
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https://github.com/krb5/krb5/commit/21e4e653d8258d525f4b6ca87797d42a8bccc282
commit 21e4e653d8258d525f4b6ca87797d42a8bccc282
Author: Greg Hudson <ghudson@mit.edu>
Date: Tue Dec 9 12:37:44 2014 -0500
Fix krb5_read_message handling [CVE-2014-5355]
In recvauth_common, do not use strcmp against the data fields of
krb5_data objects populated by krb5_read_message(), as there is no
guarantee that they are C strings. Instead, create an expected
krb5_data value and use data_eq().
In the sample user-to-user server application, check that the received
client principal name is null-terminated before using it with printf
and krb5_parse_name.
CVE-2014-5355:
In MIT krb5, when a server process uses the krb5_recvauth function, an
unauthenticated remote attacker can cause a NULL dereference by
sending a zero-byte version string, or a read beyond the end of
allocated storage by sending a non-null-terminated version string.
The example user-to-user server application (uuserver) is similarly
vulnerable to a zero-length or non-null-terminated principal name
string.
The krb5_recvauth function reads two version strings from the client
using krb5_read_message(), which produces a krb5_data structure
containing a length and a pointer to an octet sequence. krb5_recvauth
assumes that the data pointer is a valid C string and passes it to
strcmp() to verify the versions. If the client sends an empty octet
sequence, the data pointer will be NULL and strcmp() will dereference
a NULL pointer, causing the process to crash. If the client sends a
non-null-terminated octet sequence, strcmp() will read beyond the end
of the allocated storage, possibly causing the process to crash.
uuserver similarly uses krb5_read_message() to read a client principal
name, and then passes it to printf() and krb5_parse_name() without
verifying that it is a valid C string.
The krb5_recvauth function is used by kpropd and the Kerberized
versions of the BSD rlogin and rsh daemons. These daemons are usually
run out of inetd or in a mode which forks before processing incoming
connections, so a process crash will generally not result in a
complete denial of service.
Thanks to Tim Uglow for discovering this issue.
CVSSv2: AV:N/AC:L/Au:N/C:N/I:N/A:P/E:POC/RL:OF/RC:C
[tlyu@mit.edu: CVSS score]
(cherry picked from commit 102bb6ebf20f9174130c85c3b052ae104e5073ec)
ticket: 8050
version_fixed: 1.13.2
status: resolved
src/appl/user_user/server.c | 4 +++-
src/lib/krb5/krb/recvauth.c | 9 ++++++---
2 files changed, 9 insertions(+), 4 deletions(-)
diff --git a/src/appl/user_user/server.c b/src/appl/user_user/server.c
index 09ea4e0..f2b5b61 100644
--- a/src/appl/user_user/server.c
+++ b/src/appl/user_user/server.c
@@ -111,8 +111,10 @@ int main(argc, argv)
}
#endif
+ /* principal name must be sent null-terminated. */
retval = krb5_read_message(context, (krb5_pointer) &sock, &pname_data);
- if (retval) {
+ if (retval || pname_data.length == 0 ||
+ pname_data.data[pname_data.length - 1] != '\0') {
com_err ("uu-server", retval, "reading pname");
return 2;
}
diff --git a/src/lib/krb5/krb/recvauth.c b/src/lib/krb5/krb/recvauth.c
index da836283..5adc6dd 100644
--- a/src/lib/krb5/krb/recvauth.c
+++ b/src/lib/krb5/krb/recvauth.c
@@ -59,6 +59,7 @@ recvauth_common(krb5_context context,
krb5_rcache rcache = 0;
krb5_octet response;
krb5_data null_server;
+ krb5_data d;
int need_error_free = 0;
int local_rcache = 0, local_authcon = 0;
@@ -77,7 +78,8 @@ recvauth_common(krb5_context context,
*/
if ((retval = krb5_read_message(context, fd, &inbuf)))
return(retval);
- if (strcmp(inbuf.data, sendauth_version)) {
+ d = make_data((char *)sendauth_version, strlen(sendauth_version) + 1);
+ if (!data_eq(inbuf, d)) {
problem = KRB5_SENDAUTH_BADAUTHVERS;
response = 1;
}
@@ -93,8 +95,9 @@ recvauth_common(krb5_context context,
*/
if ((retval = krb5_read_message(context, fd, &inbuf)))
return(retval);
- if (appl_version && strcmp(inbuf.data, appl_version)) {
- if (!problem) {
+ if (appl_version != NULL && !problem) {
+ d = make_data(appl_version, strlen(appl_version) + 1);
+ if (!data_eq(inbuf, d)) {
problem = KRB5_SENDAUTH_BADAPPLVERS;
response = 2;
}
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