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+Date: Sun, 1 Oct 2023 11:33:26 +0200
+From: Florian Zumbiehl <florz@florz.de>
+To: exim-dev@lists.exim.org
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+Subject: [exim-dev] Hotfix for some of the ZDI vulnerabilities
+List-Id: Exim MTA development list <exim-dev.lists.exim.org>
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+Message: 1
+Status: RO
+Content-Length: 5347
+
+Hi,
+
+below you find a patch that fixes some (probably three?) of what I guess are
+the vulnerabilities reported by ZDI.
+
+Please note that the patch is only mildly tested, it is developed based on
+the git master branch, but can be applied to older versions with minor
+massaging. If you go back far enough, proxy.c was part of smtp_in.c, but if
+you adjust for that, the patch can be made to apply there, too.
+
+Obviously, I have no idea whether this actually addresses what ZDI has
+reported, but if not, these probably should be fixed, too, and if so, given
+the fact that I managed to rather easily find these vulnerabilities based
+on the information that's publicly available, I don't think there is much
+point to trying to keep this secret any longer--if anything, it's
+counterproductive.
+
+Also mind you that this is a hot fix, it's neither elegant, nor does it do
+any useful error reporting, the goal was simply to prevent out of bounds
+accesses.
+
+Florian
+
+---
+
+--- a/src/auths/external.c
++++ b/src/auths/external.c
+@@ -100,6 +100,9 @@ if (expand_nmax == 0) /* skip if rxd da
+ if ((rc = auth_prompt(CUS"")) != OK)
+ return rc;
+
++if (expand_nmax != 1)
++ return FAIL;
++
+ if (ob->server_param2)
+ {
+ uschar * s = expand_string(ob->server_param2);
+--- a/src/auths/spa.c
++++ b/src/auths/spa.c
+@@ -165,12 +165,18 @@ if (auth_get_no64_data(&data, msgbuf) !=
+ return FAIL;
+
+ /* dump client response */
+-if (spa_base64_to_bits(CS &response, sizeof(response), CCS data) < 0)
++int l = spa_base64_to_bits(CS &response, sizeof(response), CCS data);
++if (l < 0)
+ {
+ DEBUG(D_auth) debug_printf("auth_spa_server(): bad base64 data in "
+ "response: %s\n", data);
+ return FAIL;
+ }
++if(l < (char *)&response.buffer - (char *)&response)return FAIL;
++unsigned long o = IVAL(&response.uUser.offset, 0);
++if((l < o) || (l - o < SVAL(&response.uUser.len, 0)))return FAIL;
++o = IVAL(&response.ntResponse.offset, 0);
++if((l < o) || (l - o < 24))return FAIL;
+
+ /***************************************************************
+ PH 07-Aug-2003: The original code here was this:
+@@ -345,7 +351,10 @@ if (!smtp_read_response(sx, US buffer, b
+
+ /* convert the challenge into the challenge struct */
+ DSPA("\n\n%s authenticator: challenge (%s)\n\n", ablock->name, buffer + 4);
+-spa_base64_to_bits(CS (&challenge), sizeof(challenge), CCS (buffer + 4));
++int l = spa_base64_to_bits(CS (&challenge), sizeof(challenge), CCS (buffer + 4));
++if((l < 0) || (l < (char *)&challenge.buffer - (char *)&challenge))return FAIL;
++unsigned long o = IVAL(&challenge.uDomain.offset, 0);
++if((l < o) || (l - o < SVAL(&challenge.uDomain.len, 0)))return FAIL;
+
+ spa_build_auth_response(&challenge, &response, CS username, CS password);
+ spa_bits_to_base64(US msgbuf, US &response, spa_request_length(&response));
+--- a/src/smtp_in.c
++++ b/src/smtp_in.c
+@@ -1172,6 +1172,8 @@ while (capacity > 0)
+ do { ret = read(fd, to, 1); } while (ret == -1 && errno == EINTR && !had_command_timeout);
+ if (ret == -1)
+ return -1;
++ if (!ret)
++ break;
+ have++;
+ if (last)
+ return have;
+@@ -1320,6 +1322,8 @@ if ((ret == PROXY_INITIAL_READ) && (memc
+ goto proxyfail;
+ }
+
++ if (ret < 16)
++ goto proxyfail;
+ /* The v2 header will always be 16 bytes per the spec. */
+ size = 16 + ntohs(hdr.v2.len);
+ DEBUG(D_receive) debug_printf("Detected PROXYv2 header, size %d (limit %d)\n",
+@@ -1340,7 +1344,7 @@ if ((ret == PROXY_INITIAL_READ) && (memc
+ {
+ retmore = read(fd, (uschar*)&hdr + ret, size-ret);
+ } while (retmore == -1 && errno == EINTR && !had_command_timeout);
+- if (retmore == -1)
++ if (retmore < 1)
+ goto proxyfail;
+ ret += retmore;
+ DEBUG(D_receive) debug_printf("PROXYv2: have %d/%d required octets\n", ret, size);
+@@ -1362,6 +1366,8 @@ if (ret >= 16 && memcmp(&hdr.v2, v2sig,
+ switch (hdr.v2.fam)
+ {
+ case 0x11: /* TCPv4 address type */
++ if (ret < 28)
++ goto proxyfail;
+ iptype = US"IPv4";
+ tmpaddr.sin_addr.s_addr = hdr.v2.addr.ip4.src_addr;
+ inet_ntop(AF_INET, &tmpaddr.sin_addr, CS &tmpip, sizeof(tmpip));
+@@ -1388,6 +1394,8 @@ if (ret >= 16 && memcmp(&hdr.v2, v2sig,
+ proxy_external_port = tmpport;
+ goto done;
+ case 0x21: /* TCPv6 address type */
++ if (ret < 52)
++ goto proxyfail;
+ iptype = US"IPv6";
+ memmove(tmpaddr6.sin6_addr.s6_addr, hdr.v2.addr.ip6.src_addr, 16);
+ inet_ntop(AF_INET6, &tmpaddr6.sin6_addr, CS &tmpip6, sizeof(tmpip6));
+@@ -1446,10 +1454,13 @@ else if (ret >= 8 && memcmp(hdr.v1.line,
+ goto proxyfail;
+ ret += r2;
+
++ if(ret > 107)
++ goto proxyfail;
++ hdr.v1.line[ret] = 0;
+ p = string_copy(hdr.v1.line);
+ end = memchr(p, '\r', ret - 1);
+
+- if (!end || (end == (uschar*)&hdr + ret) || end[1] != '\n')
++ if (!end || end[1] != '\n')
+ {
+ DEBUG(D_receive) debug_printf("Partial or invalid PROXY header\n");
+ goto proxyfail;
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