Two relatively minor (IMHO) security issues in Exim were raised over the
Christmas break. The patches below address them for the 4.43 release. The same
patches will probably easily retrofit onto quite a number of prior releases. I
have also put these fixes into the current source, and made a new snapshot for
testing in
ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/Testing/exim-snapshot.tar.gz
ftp://ftp.csx.cam.ac.uk/pub/software/email/exim/Testing/exim-snapshot.tar.gz.sig
In addition to the security patches, this snapshot contains some bug fixes and
tidies that were reported by testers of the previous snapshot.
Discussion of security issues
- -----------------------------
1. The function host_aton() can overflow a buffer if it is presented with an
illegal IPv6 address that has more than 8 components. The input to this
function is supposed to be checked; the report said that an unchecked value
could be passed via the command line (without specifying which command line
option, annoyingly). I found one such case, which was a call do a dnsdb
lookup for a PTR record, as part of testing expansions using -be. The first
patch below fixes this - as it happens, this change had already been made to
the current source.
The report stated that Exim was running as "exim" when the problem occurred:
with -be, Exim runs as the calling user. Therefore, either the report was
wrong, or there is another case that I could not find. However, if there is
another case, it will now be covered by the second patch below, which puts a
test into the host_aton() function itself. (This should, of course, have
been there all the time, as a bit of defensive programming, but hey, I'm
only human. :-)
2. The second report described a buffer overflow in the function
spa_base64_to_bits(), which is part of the code for SPA authentication. This
code originated in the Samba project. The overflow can be exploited only if
you are using SPA authentication. The remaining patches below fix this
problem by adding a buffer length parameter to the problem function. I have
tested that SPA authentication still works, but I don't have the tools to
test that an attempt to exploit the overflow is now detected.
- --
Philip Hazel University of Cambridge Computing Service,
ph10@??? Cambridge, England. Phone: +44 1223 334714.
- -----PATCHES-------------------------------------------------------------
*** exim-4.43/src/lookups/dnsdb.c Tue Oct 5 09:32:08 2004
- --- dnsdb.c Wed Dec 29 09:36:13 2004
***************
*** 125,131 ****
/* If the type is PTR, we have to construct the relevant magic lookup
key. This code is now in a separate function. */
! if (type == T_PTR)
{
dns_build_reverse(keystring, buffer);
keystring = buffer;
- --- 125,131 ----
/* If the type is PTR, we have to construct the relevant magic lookup
key. This code is now in a separate function. */
! if (type == T_PTR && string_is_ip_address(keystring, NULL))
{
dns_build_reverse(keystring, buffer);
keystring = buffer;
*** exim-4.43/src/host.c Tue Oct 5 09:32:08 2004
- --- host.c Wed Dec 29 09:43:17 2004
***************
*** 710,721 ****
if (*p == ':') p++;
! /* Split the address into components separated by colons. */
while (*p != 0)
{
int len = Ustrcspn(p, ":");
if (len == 0) nulloffset = ci;
component[ci++] = p;
p += len;
if (*p == ':') p++;
- --- 754,771 ----
if (*p == ':') p++;
! /* Split the address into components separated by colons. The input address
! is supposed to be checked for syntax. There was a case where this was
! overlooked; to guard against that happening again, check here and crash if
! there is a violation. */
while (*p != 0)
{
int len = Ustrcspn(p, ":");
if (len == 0) nulloffset = ci;
+ if (ci > 7) log_write(0, LOG_MAIN|LOG_PANIC_DIE,
+ "Internal error: invalid IPv6 address \"%s\" passed to host_aton()",
+ address);
component[ci++] = p;
p += len;
if (*p == ':') p++;
*** exim-4.43/src/auths/auth-spa.c Tue Oct 5 09:32:08 2004
- --- auth-spa.c Wed Dec 29 10:55:58 2004
***************
*** 404,411 ****
*out = '\0';
}
int
! spa_base64_to_bits (char *out, const char *in)
/* base 64 to raw bytes in quasi-big-endian order, returning count of bytes */
{
int len = 0;
- --- 406,416 ----
*out = '\0';
}
+
+ /* The outlength parameter was added by PH, December 2004 */
+
int
! spa_base64_to_bits (char *out, int outlength, const char *in)
/* base 64 to raw bytes in quasi-big-endian order, returning count of bytes */
{
int len = 0;
***************
*** 418,423 ****
- --- 423,430 ----
do
{
+ if (len >= outlength) /* Added by PH */
+ return (-1); /* Added by PH */
digit1 = in[0];
if (DECODE64 (digit1) == BAD)
return (-1);
***************
*** 435,445 ****
- --- 442,456 ----
++len;
if (digit3 != '=')
{
+ if (len >= outlength) /* Added by PH */
+ return (-1); /* Added by PH */
*out++ =
((DECODE64 (digit2) << 4) & 0xf0) | (DECODE64 (digit3) >> 2);
++len;
if (digit4 != '=')
{
+ if (len >= outlength) /* Added by PH */
+ return (-1); /* Added by PH */
*out++ = ((DECODE64 (digit3) << 6) & 0xc0) | DECODE64 (digit4);
++len;
}
*** exim-4.43/src/auths/auth-spa.h Tue Oct 5 09:32:08 2004
- --- auth-spa.h Wed Dec 29 10:55:58 2004
***************
*** 9,14 ****
- --- 11,19 ----
* All the code used here was torn by Marc Prud'hommeaux out of the
* Samba project (by Andrew Tridgell, Jeremy Allison, and others).
*/
+
+ /* December 2004: The spa_base64_to_bits() function has no length checking in
+ it. I have added a check. PH */
/* It seems that some systems have existing but different definitions of some
of the following types. I received a complaint about "int16" causing
***************
*** 75,81 ****
#define spa_request_length(ptr) (((ptr)->buffer - (uint8x*)(ptr)) + (ptr)->bufIndex)
void spa_bits_to_base64 (unsigned char *, const unsigned char *, int);
! int spa_base64_to_bits(char *, const char *);
void spa_build_auth_response (SPAAuthChallenge *challenge,
SPAAuthResponse *response, char *user, char *password);
void spa_build_auth_request (SPAAuthRequest *request, char *user,
- --- 80,86 ----
#define spa_request_length(ptr) (((ptr)->buffer - (uint8x*)(ptr)) + (ptr)->bufIndex)
void spa_bits_to_base64 (unsigned char *, const unsigned char *, int);
! int spa_base64_to_bits(char *, int, const char *);
void spa_build_auth_response (SPAAuthChallenge *challenge,
SPAAuthResponse *response, char *user, char *password);
void spa_build_auth_request (SPAAuthRequest *request, char *user,
*** exim-4.43/src/auths/spa.c Tue Oct 5 09:32:08 2004
- --- spa.c Wed Dec 29 10:55:58 2004
***************
*** 133,139 ****
return FAIL;
}
! if (spa_base64_to_bits((char *)(&request), (const char *)(data)) < 0)
{
DEBUG(D_auth) debug_printf("auth_spa_server(): bad base64 data in "
"request: %s\n", data);
- --- 135,141 ----
return FAIL;
}
! if (spa_base64_to_bits((char *)(&request), sizeof(request), (const char *)(data)) < 0)
{
DEBUG(D_auth) debug_printf("auth_spa_server(): bad base64 data in "
"request: %s\n", data);
***************
*** 153,159 ****
}
/* dump client response */
! if (spa_base64_to_bits((char *)(&response), (const char *)(data)) < 0)
{
DEBUG(D_auth) debug_printf("auth_spa_server(): bad base64 data in "
"response: %s\n", data);
- --- 155,161 ----
}
/* dump client response */
! if (spa_base64_to_bits((char *)(&response), sizeof(response), (const char *)(data)) < 0)
{
DEBUG(D_auth) debug_printf("auth_spa_server(): bad base64 data in "
"response: %s\n", data);
***************
*** 319,325 ****
/* convert the challenge into the challenge struct */
DSPA("\n\n%s authenticator: challenge (%s)\n\n",
ablock->name, buffer + 4);
! spa_base64_to_bits ((char *)(&challenge), (const char *)(buffer + 4));
spa_build_auth_response (&challenge, &response,
CS username, CS password);
- --- 324,330 ----
/* convert the challenge into the challenge struct */
DSPA("\n\n%s authenticator: challenge (%s)\n\n",
ablock->name, buffer + 4);
! spa_base64_to_bits ((char *)(&challenge), sizeof(challenge), (const char *)(buffer + 4));
spa_build_auth_response (&challenge, &response,
CS username, CS password);
