From: kevin lyda (kevin at domain ie.suberic.net)
Date: Wed 26 Jun 2002 - 22:55:53 IST
oh wait, there's more. the default to PAMAuthenticationViaKbdInt is yes,
that appears to be bad. set it to no.
----- Forwarded message from Markus Friedl <markus at domain openbsd.org> -----
Date: Wed, 26 Jun 2002 21:08:14 +0200
From: Markus Friedl <markus at domain openbsd.org>
To: misc at domain openbsd.org
Subject: Revised OpenSSH Security Advisory (adv.iss)
This is the 2nd revision of the Advisory.
1. Versions affected:
Serveral versions of OpenSSH's sshd between 2.3.1 and 3.3
contain an input validation error that can result in an
integer overflow and privilege escalation.
All versions between 2.3.1 and 3.3 contain a bug in the
PAMAuthenticationViaKbdInt code.
All versions between 2.9.9 and 3.3 contain a bug in the
ChallengeResponseAuthentication code.
OpenSSH 3.4 and later are not affected.
OpenSSH 3.2 and later prevent privilege escalation if
UsePrivilegeSeparation is enabled in sshd_config. OpenSSH
3.3 enables UsePrivilegeSeparation by default.
Although some earlier versions are not affected upgrading
to OpenSSH 3.4 is recommended, because OpenSSH 3.4 adds
checks for a class of potential bugs.
2. Impact:
This bug can be exploited remotely if
ChallengeResponseAuthentication
is enabled in sshd_config.
Affected are at least systems supporting s/key over
SSH protocol version 2 (OpenBSD, FreeBSD and NetBSD
as well as other systems supporting s/key with SSH).
Exploitablitly of systems using
PAMAuthenticationViaKbdInt
has not been verified.
3. Short-Term Solution:
Disable ChallengeResponseAuthentication in sshd_config.
and
Disable PAMAuthenticationViaKbdInt in sshd_config.
Alternatively you can prevent privilege escalation
if you enable UsePrivilegeSeparation in sshd_config.
4. Solution:
Upgrade to OpenSSH 3.4 or apply the following patches.
5. Credits:
ISS.
Appendix:
A:
Index: auth2-chall.c
===================================================================
RCS file: /cvs/src/usr.bin/ssh/auth2-chall.c,v
retrieving revision 1.18
diff -u -r1.18 auth2-chall.c
--- auth2-chall.c 19 Jun 2002 00:27:55 -0000 1.18
+++ auth2-chall.c 26 Jun 2002 09:37:03 -0000
at domain at domain -256,6 +256,8 at domain at domain
authctxt->postponed = 0; /* reset */
nresp = packet_get_int();
+ if (nresp > 100)
+ fatal("input_userauth_info_response: nresp too big %u", nresp);
if (nresp > 0) {
response = xmalloc(nresp * sizeof(char*));
for (i = 0; i < nresp; i++)
B:
Index: auth2-pam.c
===================================================================
RCS file: /var/cvs/openssh/auth2-pam.c,v
retrieving revision 1.12
diff -u -r1.12 auth2-pam.c
--- auth2-pam.c 22 Jan 2002 12:43:13 -0000 1.12
+++ auth2-pam.c 26 Jun 2002 10:12:31 -0000
at domain at domain -140,6 +140,15 at domain at domain
nresp = packet_get_int(); /* Number of responses. */
debug("got %d responses", nresp);
+
+ if (nresp != context_pam2.num_expected)
+ fatal("%s: Received incorrect number of responses "
+ "(expected %u, received %u)", __func__, nresp,
+ context_pam2.num_expected);
+
+ if (nresp > 100)
+ fatal("%s: too many replies", __func__);
+
for (i = 0; i < nresp; i++) {
int j = context_pam2.prompts[i];
----- End forwarded message -----
-- kevin at domain suberic.net that a believer is happier than a skeptic is no more to fork()'ed on 37058400 the point than the fact that a drunken man is happier meatspace place: inle than a sober one. the happiness of credulity is a http://suberic.net/~kevin cheap & dangerous quality -- g.b. shaw
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