Red Hat Bugzilla – Bug 963769
cracklib-check allows dictionary based passwords with simple modifications
Last modified: 2017-09-22 09:15:43 EDT
Description of problem:
When using simple English word list (from package words), cracklib-check doesn't recognize passwords with simple modifications as based on dictionary words.
Version-Release number of selected component (if applicable):
Steps to Reproduce:
1. create-cracklib-dict /usr/share/dict/words
2. echo "d.ncing" | cracklib-check
3. echo "d@ncing" | cracklib-check
4. echo "glo8ulin" | cracklib-check
5. echo "dancingdancing" | cracklib-check
6. echo "ancingd" | cracklib-check # "dancing" barrel-shifted by one letter
7. echo "1dancing1" | cracklib-check
8. echo "aca7alectic" | cracklib-check
d.ncing: it is based on a dictionary word
d@ncing: it is based on a dictionary word
glo8ulin: it is based on a dictionary word
dancingdancing: it is based on a dictionary word
ancingd: it is based on a dictionary word
1dancing1: it is based on a dictionary word
aca7alectic: it is based on a dictionary word
Considering that passwords such as "-*!dancing,-=" are rejected, not rejecting much simpler changes/substitutions is unexpected.
As most of those modifications are present in standard rules used by John The Ripper they should be rejected by cracklib.
While some of those cases are introducing completely new tests, the list of missing leetspeak substitutions is quite glaring.
Proposed list of substitutions:
@ -> a
4 -> a
8 -> b (B)
3 -> e (E)
6 -> g
9 -> g
! -> i or l
1 -> i or l
$ -> s
5 -> s
7 -> t (T)
+ -> t
| -> i or l
Created attachment 749442 [details]
partial fix: add roll-left and roll-right constructors
Created attachment 749443 [details]
partial fix: add more l33t-ish substitutions
These aren't integrated properly, but doing it in a way that wouldn't explode the destructors list would require redoing a few layers of logic.
Regarding patch in Comment #2: I don't know how the code later searches if the word is in wordlist or not, but I know that pam_cracklib does check if a password doesn't contain words as a substring of "passwordpassword". This finds not only repetitions but such simple barrel shifts like in the "ancingd" case.
Regarding patch in Comment #3: I'm not sure if I read the patch correctly, but the a -> . substitution was more to show that obfuscating a single character is enough to render cracklib useless, not an actual "l33t speak" substitution.
And second "I'm not sure if I read the patch correctly" is the 8 -> B substitution: doesn't cracklib do a case insensitive search over its wordlist?
(In reply to Hubert Kario from comment #4)
> Regarding patch in Comment #2: I don't know how the code later searches if
> the word is in wordlist or not, but I know that pam_cracklib does check if a
> password doesn't contain words as a substring of "passwordpassword". This
> finds not only repetitions but such simple barrel shifts like in the
> "ancingd" case.
The pam_cracklib module (and the cracklib python module, and apparently everything else that uses cracklib) implements additional logic beyond what cracklib does, so cracklib-check doesn't benefit from those efforts.
> Regarding patch in Comment #3: I'm not sure if I read the patch correctly,
> but the a -> . substitution was more to show that obfuscating a single
> character is enough to render cracklib useless, not an actual "l33t speak"
> And second "I'm not sure if I read the patch correctly" is the 8 -> B
> substitution: doesn't cracklib do a case insensitive search over its
So it does. That rule should be discarded from the patch, then. As for the larger point, you're right, cracklib's doesn't catch everything.
I don't think this is RHEL-6 material. This should be changed in Fedora and RHEL-7 if at all.
This request was evaluated by Red Hat Product Management for
inclusion in the current release of Red Hat Enterprise Linux.
Because the affected component is not scheduled to be updated
in the current release, Red Hat is unable to address this
request at this time.
Red Hat invites you to ask your support representative to
propose this request, if appropriate, in the next release of
Red Hat Enterprise Linux.
Red Hat Enterprise Linux 6 transitioned to the Production 3 Phase on May 10, 2017. During the Production 3 Phase, Critical impact Security Advisories (RHSAs) and selected Urgent Priority Bug Fix Advisories (RHBAs) may be released as they become available.
The official life cycle policy can be reviewed here:
This issue does not appear to meet the inclusion criteria for the Production Phase 3 and will be marked as CLOSED/WONTFIX. If this remains a critical requirement, please re-open the BZ and request a re-evaluation of the issue, citing a clear business justification.