Bug 2458516 (CVE-2026-4890)

Summary:	CVE-2026-4890 dnsmasq: NSEC bitmap parsing infinite loop
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security DevOps Team <prodsec-dev>
Status:	NEW ---	QA Contact:
Severity:	high	Docs Contact:
Priority:	high
Version:	unspecified	CC:	rhel-process-autobot, security-response-team, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:	A denial of service vulnerability was discovered in dnsmasq's DNSSEC validation. When parsing NSEC and NSEC3 bitmap records, the window iteration logic fails to account for the 2-byte window header when advancing through the bitmap data. A specially crafted DNS response with a zero-length bitmap can cause an infinite loop, making dnsmasq unresponsive to all queries.	Story Points:	---
Clone Of:		Environment:
Last Closed:		Type:	---
Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Deadline:	2026-05-09

Description OSIDB Bzimport 2026-04-14 22:39:35 UTC

NSEC/NSEC3 bitmap window iteration in dnssec.c advances by p[1] instead of p[1] + 2, missing the 2-byte window header. When bitmap_length=0, neither rdlen nor p change, creating an infinite loop. Two instances at dnssec.c:1290 and dnssec.c:1450. Reachable before RRSIG validation so no valid signatures are needed. One of the two sites was coincidentally fixed in 2.92. Fix: add +2 to both the pointer advance and rdlen decrement.

Comment 2 errata-xmlrpc 2026-05-19 16:10:31 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 10

Via RHSA-2026:19158 https://access.redhat.com/errata/RHSA-2026:19158

Comment 3 errata-xmlrpc 2026-05-19 21:41:08 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9

Via RHSA-2026:19373 https://access.redhat.com/errata/RHSA-2026:19373

Comment 4 errata-xmlrpc 2026-05-26 04:57:23 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 8

Via RHSA-2026:20589 https://access.redhat.com/errata/RHSA-2026:20589

Comment 5 errata-xmlrpc 2026-07-01 21:09:39 UTC

This issue has been addressed in the following products:

  Red Hat Enterprise Linux 9.6 Extended Update Support

Via RHSA-2026:34508 https://access.redhat.com/errata/RHSA-2026:34508

Comment 6 errata-xmlrpc 2026-07-22 12:54:56 UTC

This issue has been addressed in the following products:

  Red Hat OpenShift Container Platform 4.19

Via RHSA-2026:40762 https://access.redhat.com/errata/RHSA-2026:40762