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sredird LogMsg() Format String Bug and HandleCPCCommand() Buffer Overflow May Let Remote Users Execute Arbitrary Code
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SecurityTracker Alert ID: 1011038
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SecurityTracker URL: http://securitytracker.com/id?1011038
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CVE Reference: GENERIC-MAP-NOMATCH
(Links to External Site)
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Date: Aug 24 2004
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Impact: Execution of arbitrary code via network, Root access via network, User access via network
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Version(s): 2.2.1
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Description: Two vulnerabilities were reported in sredird. A remote user can gain root access on the target system.
Max Vozeler reported that there is a format string flaw in the LogMsg() function in 'sredird.c'. User-supplied data can be passed
to the LogMsg() function without a formatting string by the HandleCPCCommand() function. A remote user can cause arbitrary code
to be executed with the privileges of the sredird process. On some distributions, this may be root privileges.
It is also reported
that there is a stack overflow in the HandleCPCCommand() function. A remote user may be able to trigger the overflow to execute
arbitrary code.
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Impact: A remote user can execute arbitrary code with the privileges of sredird.
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Solution: No upstream solution was available at the time of this entry.
A fix is pending for sredird on Debian GNU/Linux.
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Vendor URL: www.ibiblio.org/pub/Linux/system/serial/sredird-2.2.1.tar.gz (Links to External Site)
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Cause: Boundary error, Input validation error, State error
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Underlying OS: Linux (Any), UNIX (Any)
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Reported By: Max Vozeler <max@hinterhof.net>
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Message History:
None.
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Source Message Contents
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Date: Fri, 20 Aug 2004 20:00:22 +0200
From: Max Vozeler <max@hinterhof.net>
Subject: sredird: remote root vulnerabilities
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Package: sredird
Version: 2.2.1-1
Severity: critical
Tags: patch
Hi,
these bugs still apply.
Cheers,
Max
--
308E81E7B97963BCA0E6ED889D5BD511B7CDA2DC
----- Forwarded message from Max Vozeler <max@hinterhof.net> -----
From: Max Vozeler <max@hinterhof.net>
To: russell@coker.com.au
Cc: team@security.debian.org
Subject: sredird vulnerabilities
Date: Fri, 30 Jul 2004 14:52:24 +0200
User-Agent: Mutt/1.5.6+20040523i
Hi Russell,
[ CCing Security Team for vulns in the testing version ]
there are two bugs in sredird that can introduce security problems,
potentially leading to a remote root compromise. Affected in Debian is
the testing/unstable sredird 2.2.1-1.
Feel free to forward this info as you like. Unless you want me to delay
disclosure to the BTS for some reason, or the fixed package has already
entered testing by then, I'll file +security bugs in 10 days or so.
There are two bugs:
LogMsg() format string bug
--------------------------
sredird-2.2.1/sredird.c:
458 /* Generic log function with log level control. Uses the same log levels
459 of the syslog(3) system call */
460 void LogMsg(int LogLevel, const char * const Msg)
461 {
462 if (LogLevel <= MaxLogLevel)
463 syslog(LogLevel,Msg);
464 }
The log buffer in Msg is given to syslog() as format control string. This
can lead to overwriting of any memory locations in case the content of Msg
is controllable by an attacker. There is in fact one such place where the
input to LogMsg() is constructed from data as supplied by the client:
1365 /* Handling of COM Port Control specific commands */
1366 void HandleCPCCommand(BufferType *SockB, int PortFd, unsigned char * Command, size_t CSize)
1367 {
1368 char LogStr[TmpStrLen];
1369 char SigStr[TmpStrLen];
..
1376 /* Check wich command has been requested */
1377 switch (Command[3])
1378 {
1379 /* Signature */
1380 case TNCAS_SIGNATURE:
..
1391 /* Received client signature */
1392 strncpy(SigStr,(char *) &Command[4],CSize - 6);
1393 sprintf(LogStr,"Received client signature: %s",SigStr);
1394 LogMsg(LOG_INFO,LogStr);
The canonical fix would be to add an explicit "%s" format string to the
syslog() call in LogMsg(). (See attached sredird-log-fmt.diff)
HandleCPCCommand() stack overflow
---------------------------------
Affected is the last chunk of code in HandleCPCCommand() shown above.
LogStr is not large enough to store the largest possible output from
sprintf(). CSize is limited to 254 by the caller, minus 6, makes a max.
SigStr length of 248 bytes. After the sprintf() with 27 or so non-format
characters, the output can grow to
27 + 248 = 275 bytes
.. which is too much for LogStr[255], by 20 bytes or so. This may be
enough to overwrite precious stuff on the stack like saved eip depending
on stack layout.
Why not just replace it with snprintf()? This would solve this problem
for good. See attached patch sredird-hcpcc-bof.diff for example.
(There should be a LogStr[sizeof(LogStr)-1] = 0; after the snprintf in
the patch which I forgot to add)
Cheers,
Max
--
308E81E7B97963BCA0E6ED889D5BD511B7CDA2DC
--- sredird.c.orig 2004-05-01 21:45:49.000000000 +0200
+++ sredird.c 2004-05-01 21:46:05.000000000 +0200
@@ -460,7 +460,7 @@
void LogMsg(int LogLevel, const char * const Msg)
{
if (LogLevel <= MaxLogLevel)
- syslog(LogLevel,Msg);
+ syslog(LogLevel,"%s",Msg);
}
/* Try to lock the file given in LockFile as pid LockPid using the classical
--- sredird.c.orig 2004-05-01 22:09:28.000000000 +0200
+++ sredird.c 2004-05-01 22:10:10.000000000 +0200
@@ -1390,7 +1390,7 @@
{
/* Received client signature */
strncpy(SigStr,(char *) &Command[4],CSize - 6);
- sprintf(LogStr,"Received client signature: %s",SigStr);
+ snprintf(LogStr,sizeof(LogStr)-1,"Received client signature: %s",SigStr);
LogMsg(LOG_INFO,LogStr);
}
break;
----- End forwarded message -----
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