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From 6a7edbf6608d10ef0c707c426511e667849518d7 Mon Sep 17 00:00:00 2001
From: Jeremy Harris <jgh146exb@wizmail.org>
Date: Tue, 5 May 2020 21:15:34 +0100
Subject: [PATCH 1/2] Fix SPA authenticator, checking client-supplied data
before using it. Bug 2571
(cherry picked from commit 57aa14b216432be381b6295c312065b2fd034f86)
---
doc/ChangeLog | 5 +++++
src/auths/spa.c | 22 ++++++++++++++++------
2 files changed, 21 insertions(+), 6 deletions(-)
--- a/doc/ChangeLog
+++ b/doc/ChangeLog
@@ -62,6 +62,11 @@ JH/28 Fix the timeout on smtp response t
[from GIT master]
+JH/41 Bug 2571: Fix SPA authenticator. Running as a server, an offset supplied
+ by the client was not checked as pointing within response data before
+ being used. A malicious client could thus cause an out-of-bounds read and
+ possibly gain authentication. Fix by adding the check.
+
Exim version 4.92
-----------------
--- a/src/auths/spa.c
+++ b/src/auths/spa.c
@@ -139,7 +139,7 @@ SPAAuthChallenge challenge;
SPAAuthResponse response;
SPAAuthResponse *responseptr = &response;
uschar msgbuf[2048];
-uschar *clearpass;
+uschar *clearpass, *s;
/* send a 334, MS Exchange style, and grab the client's request,
unless we already have it via an initial response. */
@@ -197,6 +197,13 @@ that causes failure if the size of msgbu
char *p = ((char*)responseptr) + IVAL(&responseptr->uUser.offset,0);
int len = SVAL(&responseptr->uUser.len,0)/2;
+ if (p + len*2 >= CS (responseptr+1))
+ {
+ DEBUG(D_auth)
+ debug_printf("auth_spa_server(): bad uUser spec in response\n");
+ return FAIL;
+ }
+
if (len + 1 >= sizeof(msgbuf)) return FAIL;
for (i = 0; i < len; ++i)
{
@@ -245,14 +252,17 @@ spa_smb_nt_encrypt (clearpass, challenge
/* compare NT hash (LM may not be available) */
-if (memcmp(ntRespData,
- ((unsigned char*)responseptr)+IVAL(&responseptr->ntResponse.offset,0),
- 24) == 0)
- /* success. we have a winner. */
+s = (US responseptr) + IVAL(&responseptr->ntResponse.offset,0);
+if (s + 24 >= US (responseptr+1))
{
- return auth_check_serv_cond(ablock);
+ DEBUG(D_auth)
+ debug_printf("auth_spa_server(): bad ntRespData spec in response\n");
+ return FAIL;
}
+if (memcmp(ntRespData, s, 24) == 0)
+ return auth_check_serv_cond(ablock); /* success. we have a winner. */
+
/* Expand server_condition as an authorization check (PH) */
return FAIL;
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