Bug 2479808 (CVE-2026-33278)

Summary:	CVE-2026-33278 unbound: Unbound DNSSEC Validator Use-After-Free via Deep Copy Pointer Overwrite Leading to DoS and Possible Remote Code Execution
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	abhraj, rhel-process-autobot, security-response-team, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
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Doc Text:	A flaw was discovered in Unbound’s DNSSEC validator can leave it using an invalid memory pointer after certain DS sub-query validations fail due to NSEC3 budget exhaustion. This may cause crashes and could potentially allow arbitrary code execution.	Story Points:	---
Clone Of:		Environment:
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oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Bug Depends On:	2480119, 2481465
Bug Blocks:

Description OSIDB Bzimport 2026-05-19 11:56:28 UTC

Use After Free vulnerability in the DNSSEC validator of the Unbound DNS resolver. The flaw is caused by a struct-assignment bug during deep-copying of response messages when DS sub-queries need to suspend validation due to NSEC3 computational budget exhaustion (introduced in Unbound 1.19.1). The deep-copy operation overwrites the destination's rrsets pointer with the source's pointer. After the sub-query region is freed, the resumed validator dereferences this dangling pointer, triggering a crash or potentially enabling arbitrary code execution. An adversary can exploit this vulnerability by controlling a malicious DNSSEC-signed zone and querying a vulnerable Unbound instance.

Comment 2 errata-xmlrpc 2026-06-04 08:32:39 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 10

Via RHSA-2026:23231 https://access.redhat.com/errata/RHSA-2026:23231

Comment 3 errata-xmlrpc 2026-06-08 10:25:28 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9

Via RHSA-2026:24369 https://access.redhat.com/errata/RHSA-2026:24369