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fetchmail-SA-2010-02: Denial of service in debug mode w/ multichar locales

Topics:    Denial of service in debug output

Author:    Matthias Andree
Version:  1.0
Announced:  2010-05-06
Type:    Unbounded allocation of memory until exhaustion
Impact:    Denial of service
Danger:    low

CVE Name:  CVE-2010-1167
CVSSv2:    (AV:N/AC:M/Au:N/C:N/I:N/A:P/E:U/RL:O/RC:C)
CVSS scores:  3.2, Base 4.3 (Impact 2.9, Exploitability 8.6), Temporal 3.2
    This is calculated without Environmental Score.
URL:    http://www.fetchmail.info/fetchmail-SA-2010-02.txt
Project URL:  http://www.fetchmail.info/

Affects:  fetchmail releases 4.6.3 up to and including 6.3.16

Not affected:  fetchmail release 6.3.17 and newer

Corrected:  2010-04-24 Git, required commits:
    167fa2093e82f891eb2fcb6eaa0b1eb3685f44e3
    ec06293134b85876f9201d8a52b844c41581b2b3

    2010-04-30 fetchmail 6.3.17-pre1 tarball

    2010-05-06 fetchmail 6.3.17 release tarball


0. Release history
==================

2010-04-18 0.1  first draft (visible in SVN and through oss-security)
2010-04-19 0.2  add note announcements may appear before releases
2010-04-20 0.3  add CVE name, fix Type:
2010-04-24 0.4  revise patch
2010-04-29 0.5  add info on contributing/mitigating factors
2010-06-05 1.0  complete


1. Background
=============

fetchmail is a software package to retrieve mail from remote POP2, POP3,
IMAP, ETRN or ODMR servers and forward it to local SMTP, LMTP servers or
message delivery agents. It supports SSL and TLS security layers through
the OpenSSL library, if enabled at compile time and if also enabled at
run time.


2. Problem description and Impact
=================================

In debug mode (-v -v), fetchmail prints information that was obtained from the
upstream server (POP3 UIDL lists) or from message headers retrieved from it.
  If printing such information fails, for instance because there are invalid
multibyte character sequences in this information (message headers), fetchmail
will misinterpret this condition, and believe that the buffer was too small,
and reallocate a bigger one (with linearly increasing buffer size), and repeat,
until the allocation fails. At that point, fetchmail will abort.

The exact combination of contributing and mitigating factors is not
fully understood; GNU glibc 2.7 and 2.10.1 on i586 report EILSEQ when
printing invalid sequences through a %.*s format string in multibyte
locales such as de_DE.UTF-8; NetBSD 5, FreeBSD 8 and Solaris 10 do not.
However, the issue is a genuine fetchmail bug that deserves a fix.

Note that the "Affects:" line above may be inaccurate, and it may be that
versions before 5.6.6 are actually unaffected.  The author was unable to
compile such old fetchmail versions to verify the existence of the bug.
  Given that other security issues are present in such versions, those should
not be used, and the wider version range was listed as vulnerable to err
towards the safe.


3. Solution
===========

There are two alternatives, either of them by itself is sufficient:

a. Apply the patch found in section B of this announcement to
   fetchmail 6.3.14 or newer, recompile and reinstall it.

b. Install fetchmail 6.3.17 or newer after it will have become available.
   (Note that the announcements may be publicly visible quite some time
   before the release is made, particularly for minor bugs.)
   The fetchmail source code is always available from
   <http://developer.berlios.de/project/showfiles.php?group_id=1824>.


4. Workaround
=============

Run fetchmail with at most one -v (--verbose) option.


A. Copyright, License and Warranty
==================================

(C) Copyright 2010 by Matthias Andree, <matthias.andree@gmx.de>.
Some rights reserved.

This work is licensed under the Creative Commons
Attribution-Noncommercial-No Derivative Works 3.0 Germany License.
To view a copy of this license, visit
http://creativecommons.org/licenses/by-nc-nd/3.0/de/ or send a letter to

Creative Commons
171 Second Street
Suite 300
SAN FRANCISCO, CALIFORNIA 94105
USA


THIS WORK IS PROVIDED FREE OF CHARGE AND WITHOUT ANY WARRANTIES.
Use the information herein at your own risk.


B. Patch to remedy the problem
==============================

Note that when taking this from a GnuPG clearsigned file, the lines
starting with a "-" character are prefixed by another "- " (dash +
blank) combination. Either feed this file through GnuPG to strip them,
or strip them manually. You may want to use the "-p1" flag to patch.

Whitespace differences can usually be ignored by invoking "patch -l",
so try this if the patch does not apply.

diff --git a/rfc822.c b/rfc822.c
index 6f2dbf3..dbcda32 100644
- --- a/rfc822.c
+++ b/rfc822.c
@@ -25,6 +25,7 @@ MIT license.  Compile with -DMAIN to build the demonstrator.
 #include  <stdlib.h>
 
 #include "fetchmail.h"
+#include "sdump.h"
 
 #ifndef MAIN
 #include "i18n.h"
@@ -74,9 +75,10 @@ char *reply_hack(
     }
 
 #ifndef MAIN
- -    if (outlevel >= O_DEBUG)
- -  report_build(stdout, GT_("About to rewrite %.*s...\n"),
- -      (int)BEFORE_EOL(buf), buf);
+    if (outlevel >= O_DEBUG) {
+  report_build(stdout, GT_("About to rewrite %s...\n"), (cp = sdump(buf, BEFORE_EOL(buf))));
+  xfree(cp);
+    }
 
     /* make room to hack the address; buf must be malloced */
     for (cp = buf; *cp; cp++)
@@ -211,9 +213,12 @@ char *reply_hack(
     }
 
 #ifndef MAIN
- -    if (outlevel >= O_DEBUG)
- -  report_complete(stdout, GT_("...rewritten version is %.*s.\n"),
- -      (int)BEFORE_EOL(buf), buf);
+    if (outlevel >= O_DEBUG) {
+  report_complete(stdout, GT_("...rewritten version is %s.\n"),
+      (cp = sdump(buf, BEFORE_EOL(buf))));
+  xfree(cp)
+    }
+
 #endif /* MAIN */
     *length = strlen(buf);
     return(buf);
diff --git a/uid.c b/uid.c
index fdc6f5d..9a62ee2 100644
- --- a/uid.c
+++ b/uid.c
@@ -20,6 +20,7 @@
 
 #include "fetchmail.h"
 #include "i18n.h"
+#include "sdump.h"
 
 /*
  * Machinery for handling UID lists live here.  This is mainly to support
@@ -249,8 +250,11 @@ void initialize_saved_lists(struct query *hostlist, const char *idfile)
       {
     report_build(stdout, GT_("Old UID list from %s:"), 
            ctl->server.pollname);
- -    for (idp = ctl->oldsaved; idp; idp = idp->next)
- -        report_build(stdout, " %s", idp->id);
+    for (idp = ctl->oldsaved; idp; idp = idp->next) {
+        char *t = sdump(idp->id, strlen(idp->id));
+        report_build(stdout, " %s", t);
+        free(t);
+    }
     if (!idp)
         report_build(stdout, GT_(" <empty>"));
     report_complete(stdout, "\n");
@@ -260,8 +264,11 @@ void initialize_saved_lists(struct query *hostlist, const char *idfile)
   if (uidlcount)
   {
       report_build(stdout, GT_("Scratch list of UIDs:"));
- -      for (idp = scratchlist; idp; idp = idp->next)
- -    report_build(stdout, " %s", idp->id);
+      for (idp = scratchlist; idp; idp = idp->next) {
+    char *t = sdump(idp->id, strlen(idp->id));
+    report_build(stdout, " %s", t);
+    free(t);
+      }
       if (!idp)
     report_build(stdout, GT_(" <empty>"));
       report_complete(stdout, "\n");
@@ -517,8 +524,11 @@ void uid_swap_lists(struct query *ctl)
       report_build(stdout, GT_("Merged UID list from %s:"), ctl->server.pollname);
   else
       report_build(stdout, GT_("New UID list from %s:"), ctl->server.pollname);
- -  for (idp = dofastuidl ? ctl->oldsaved : ctl->newsaved; idp; idp = idp->next)
- -      report_build(stdout, " %s = %d", idp->id, idp->val.status.mark);
+  for (idp = dofastuidl ? ctl->oldsaved : ctl->newsaved; idp; idp = idp->next) {
+      char *t = sdump(idp->id, strlen(idp->id));
+      report_build(stdout, " %s = %d", t, idp->val.status.mark);
+      free(t);
+        }
   if (!idp)
       report_build(stdout, GT_(" <empty>"));
   report_complete(stdout, "\n");
@@ -567,8 +577,11 @@ void uid_discard_new_list(struct query *ctl)
   /* this is now a merged list! the mails which were seen in this
    * poll are marked here. */
   report_build(stdout, GT_("Merged UID list from %s:"), ctl->server.pollname);
- -  for (idp = ctl->oldsaved; idp; idp = idp->next)
- -      report_build(stdout, " %s = %d", idp->id, idp->val.status.mark);
+  for (idp = ctl->oldsaved; idp; idp = idp->next) {
+      char *t = sdump(idp->id, strlen(idp->id));
+      report_build(stdout, " %s = %d", t, idp->val.status.mark);
+      free(t);
+  }
   if (!idp)
       report_build(stdout, GT_(" <empty>"));
   report_complete(stdout, "\n");
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