Bug 1275863 (CVE-2015-2697)

Summary: CVE-2015-2697 krb5: build_principal() memory flaw
Product: [Other] Security Response Reporter: Kurt Seifried <kseifried>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED WONTFIX QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: dpal, jplans, jrusnack, nalin, pkis, rharwood, slawomir, slong
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: Doc Type: Bug Fix
Doc Text:
An out-of-bounds flaw was discovered in MIT Kerberos; the build_principal_va() function did not properly duplicate the realm. An authenticated remote attacker could possibly exploit this flaw by sending a TGS request containing a specially crafted realm field and crashing the KDC (denial of service).
Story Points: ---
Clone Of: Environment:
Last Closed: 2015-12-10 10:27:37 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Bug Depends On: 1275872    
Bug Blocks: 1275873    

Description Kurt Seifried 2015-10-28 00:53:52 UTC
The kerberos project reports:

In build_principal_va(), use k5memdup0() instead of strdup() to make a
copy of the realm, to ensure that we allocate the correct number of
bytes and do not read past the end of the input string.  This bug
affects krb5_build_principal(), krb5_build_principal_va(), and
krb5_build_principal_alloc_va().  krb5_build_principal_ext() is not
affected.

CVE-2015-2697:

In MIT krb5 1.7 and later, an authenticated attacker may be able to
cause a KDC to crash using a TGS request with a large realm field
beginning with a null byte.  If the KDC attempts to find a referral to
answer the request, it constructs a principal name for lookup using
krb5_build_principal() with the requested realm.  Due to a bug in this
function, the null byte causes only one byte be allocated for the
realm field of the constructed principal, far less than its length.
Subsequent operations on the lookup principal may cause a read beyond
the end of the mapped memory region, causing the KDC process to crash.

External reference:
https://github.com/krb5/krb5/commit/f0c094a1b745d91ef2f9a4eae2149aac026a5789

Comment 1 Kurt Seifried 2015-10-28 01:36:46 UTC
Created krb5 tracking bugs for this issue:

Affects: fedora-all [bug 1275872]