Re: (ITS#9124) Unauthenticated remote denial-of-service (Null pointer dereference in ber_skip_tag)

[stephan@srlabs.de]

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Hi Ond=C5=99ej =E2=80=94

The commit 1dbf0e9441def3d6dbc0fa8fba3c2e86fa50fa19 seems to fix the null=
 pointer dereference issue.

Using honggfuzz netdriver module, fuzzing of slapd can be accomplished re=
latively easy. You can follow the below instructions to fuzz the server:

1. Install honggfuzz (stable)

$ export CC=3Dhfuzz-clang
$ export CXX=3Dhfuzz-clang++

2. Apply attached patch (fuzz.patch)

3. Compile openldap

$ ./configure
$ make depend
$ make
$ make install

4. Create testcase directory including seeds (probably you have way bette=
r seeds then I have :), I just used ldap payloads extracted from some pca=
p's)

$ mkdir testcases

5. Start fuzzing

$ HFND_TCP_PORT=3D9090 honggfuzz -w ldap.wordlist -f testcases/ -- ./libe=
xec/slapd -d 1 -h ldap://127.0.0.1:9090

As you see, the fuzzing setup is relatively simple thanks to honggfuzz.

Hope this helps!

Note: After Cyrus SASL fixes the other issue #9123, I will request CVE id=
's for the two bugs and share them as a reference in the relevant issues =
(#9123, #9124)

Cheers

=C2=A0=C2=A0=C2=A0 -Stephan

On 11/29/19 1:06 PM, Ond=C5=99ej Kuzn=C3=ADk wrote:
> On Fri, Nov 29, 2019 at 09:08:15AM +0000, stephan@srlabs.de wrote:
>> Unauthenticated remote denial-of-service through malformed ldap packet=

>> caused by a null pointer dereference in ber_skip_tag function
>> (libraries/liblber/decode.c).
>>
>> =3D=3D4066091=3D=3D    by 0x4FD051: cancel_extop (cancel.c:52)
> Hi Stephan,
> thanks for the report, this should be fixed by commit
> 1dbf0e9441def3d6dbc0fa8fba3c2e86fa50fa19 in master.
>
> Looks like you are fuzzing the server which has been on my to do list
> for a while, many thanks for that and I'm looking forward to reading
> how you did it. Would you be willing to help the project integrate your=

> work in its testing process after you've finished?
>
> Thanks,
>

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diff --git a/servers/slapd/main.c b/servers/slapd/main.c
index f528aa951..1941ae3de 100644
--- a/servers/slapd/main.c
+++ b/servers/slapd/main.c
@@ -349,12 +349,14 @@ usage( char *name )
     );
 }
=20
-#ifdef HAVE_NT_SERVICE_MANAGER
-void WINAPI ServiceMain( DWORD argc, LPTSTR *argv )
+//#ifdef HAVE_NT_SERVICE_MANAGER
+//void WINAPI ServiceMain( DWORD argc, LPTSTR *argv )
+//#else
+#ifdef HFND_FUZZING_ENTRY_FUNCTION
+HFND_FUZZING_ENTRY_FUNCTION(int argc, char **argv) {
 #else
-int main( int argc, char **argv )
+int main( int argc, char **argv ) {
 #endif
-{
 	int		i, no_detach =3D 0;
 	int		rc =3D 1;
 	char *urls =3D NULL;

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