Bug 1869471 (CVE-2020-8621)

Summary: CVE-2020-8621 bind: Attempting QNAME minimization after forwarding can lead to an assertion failure in resolver.c
Product: [Other] Security Response Reporter: Huzaifa S. Sidhpurwala <huzaifas>
Component: vulnerabilityAssignee: Red Hat Product Security <security-response-team>
Status: CLOSED NOTABUG QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: aegorenk, anon.amish, mruprich, msehnout, pemensik, pzhukov, security-response-team, thozza, vonsch, zdohnal
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
Whiteboard:
Fixed In Version: bind 9.16.6, bind 9.17.4 Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2020-08-18 04:47:13 UTC Type: ---
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On:    
Bug Blocks: 1869469    

Description Huzaifa S. Sidhpurwala 2020-08-18 04:46:31 UTC 
As per upstream advisory:

While query forwarding and QNAME minimization are mutually incompatible, BIND did sometimes allow QNAME minimization when continuing with recursion after 'forward first' did not result in an answer.  In these cases the data used by QNAME minimization might be inconsistent, leading to an assertion failure, causing the server to exit.

If a server is configured with both QNAME minimization and 'forward first' then an attacker who can send queries to it may be able to trigger the condition that will cause the server to crash.

Servers that 'forward only' are not affected
Comment 1 Huzaifa S. Sidhpurwala 2020-08-18 04:46:34 UTC 
Acknowledgments:

Name: ISC
Upstream: Joseph Gullo
Comment 2 Huzaifa S. Sidhpurwala 2020-08-18 04:46:37 UTC 
Statement:

This flaw only affects bind >= 9.14.x. Therefore versions of bind package shipped with Red Hat Enterprise Linux are not affected by this flaw.
Comment 3 Huzaifa S. Sidhpurwala 2020-08-21 02:17:39 UTC 
External References:

https://kb.isc.org/docs/cve-2020-8621