TI-2026-30814 Aliases CVE-2026-42534 GHSA-xfcv-gp55-3wpf

Jostle logic bypass degrades resolution performance

LOW 37CWE-440Published 2026-05-20 · Updated 2026-09-01

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Attack requirements: None
Impact type: —
Confidentiality · integrity · availability: None · None · Low
Fix status: Partial Red Hat: 6 fixed, 3 without a fix

Attack profile from CVSS 4.0 · CNA. Fix status from CNA and Red Hat.

Summary

NLnet Labs Unbound up to and including version 1.25.0 has a vulnerability in the jostle logic that could defeat its purpose and degrade resolution performance. Retransmits of the same query could renew the age of slow running queries and not allow the jostle logic to see them as aged and potential targets for replacement with new queries. An adversary who can query a vulnerable Unbound and who can control a domain name server that replies slowly and/or maliciously to Unbound's queries can exploit the vulnerability and degrade the resolution performance of Unbound. When Unbound's 'num-queries-per-thread' reaches its limit, the jostle logic kicks in. When a new query comes in, half of the available queries that are also slow to resolve are candidates for replacement. The vulnerability then happens because duplicate queries that need resolution would skew the aging result by using the timestamp of the latest duplicate query instead of the original one that started the resolution effort. Cache and local data response performance remains unaffected. Coordinated attacks could raise this to a denial of resolution service. Unbound 1.25.1 contains a patch with a fix to attach an initial, non-updatable start time for incoming queries that allow the jostle logic to work as intended.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.00604 49th percentileScored 2026-11-07

Fix Partial Unbound (NLnet Labs): 1.25.1Red Hat: 4 advisoriesRed Hat: 6 fixed, 3 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: Yes
Technical impact: Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
NLnet Labs	Unbound	before 1.25.1	1.25.1	Patch available	CNA

Unbound VendorNLnet Labs Affected before 1.25.1 Fixed in 1.25.1 Patch available CNA

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:nlnetlabs:unbound::::::::	before 1.25.1	Vulnerable	NLNETLABS

cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:* Versions before 1.25.1 Vulnerable ·NLNETLABS

Remediation

Fix · CNA Unbound (NLnet Labs) Fixed in 1.25.1

Red Hat 4 advisories

RHSA-2026:37282 Released 2026-07-09 · Red Hat rating Important
unbound security update
- Red Hat Enterprise Linux AppStream (v. 8) python3-unbound-1.16.2-5.12.el8_10, unbound-1.16.2-5.12.el8_10, unbound-devel-1.16.2-5.12.el8_10 +1
RHSA-2026:36777 Released 2026-07-08 · Red Hat rating Important
unbound security update
- Red Hat Enterprise Linux AppStream (v. 9) python3-unbound-1.24.2-3.el9_8.2, unbound-1.24.2-3.el9_8.2, unbound-dracut-1.24.2-3.el9_8.2 +1
- Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) unbound-devel-1.24.2-3.el9_8.2
RHSA-2026:36320 Released 2026-07-07 · Red Hat rating Important
unbound security update
- Red Hat Enterprise Linux AppStream (v. 10) python3-unbound-1.24.2-7.el10_2.2, unbound-1.24.2-7.el10_2.2, unbound-anchor-1.24.2-7.el10_2.2 +3
- Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) unbound-devel-1.24.2-7.el10_2.2

Show 1 more Red Hat advisories

RHSA-2026:24013 Released 2026-06-07 · Red Hat rating Important
Red Hat Hardened Images RPMs bug fix and enhancement update
- Red Hat Hardened Images python3-unbound-1.25.1-2.hum1@aarch64, python3-unbound-1.25.1-2.hum1@x86_64, unbound-1.25.1-2.hum1@aarch64 +14

Fixed in the same release

Records fixed by the same vendor advisory or release, as the CNA lists them.

Release · 2026-05-20
NLnet Labs Unbound 1.25.1
11 records Highest priority Priority MEDIUM 3 MEDIUM, 8 LOW
Other records, highest priority first
- TI-2026-25690 Possible arbitrary code execution during DNSSEC validationPriority MEDIUM 50
- TI-2026-31146 Crash during DNSSEC validation of malicious contentPriority MEDIUM 45
- TI-2026-31135 Heap overflow with multiple NSID, COOKIE, PADDING EDNS optionsPriority MEDIUM 45
Show all 11 records →

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

Product	Status	Plan or fix
Red Hat Enterprise Linux 6	Affected	No fix yet
Red Hat Enterprise Linux 7	Affected	No fix yet
Red Hat OpenShift Container Platform 4	Affected	No fix yet
Red Hat Enterprise Linux AppStream (v. 10)	Fixed	RHSA-2026:36320
Red Hat Enterprise Linux AppStream (v. 8)	Fixed	RHSA-2026:37282
Red Hat Enterprise Linux AppStream (v. 9)	Fixed	RHSA-2026:36777
Red Hat Enterprise Linux CodeReady Linux Builder (v. 10)	Fixed	RHSA-2026:36320
Red Hat Enterprise Linux CodeReady Linux Builder (v. 9)	Fixed	RHSA-2026:36777
Red Hat Hardened Images	Fixed	RHSA-2026:24013

Timeline

2026-10-02 Threatist record created from CVE-2026-42534
2026-10-03 Alias added: GHSA-xfcv-gp55-3wpf
2026-10-25 EPSS moved to the below the 50th percentile

References

Advisory 1

https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-42534.txt

TI-2026-25690 Possible arbitrary code execution during DNSSEC validation CVSS 4.0CRITICAL 9.1
TI-2026-56302 Heap buffer overflow and possible Remote Code Execution when digesting DNSKEY CVSS 4.0CRITICAL 9.1
TI-2026-31146 Crash during DNSSEC validation of malicious content CVSS 4.0HIGH 8.7
TI-2026-31135 Heap overflow with multiple NSID, COOKIE, PADDING EDNS options CVSS 4.0HIGH 8.7
TI-2026-36436 Routinator crashes on specifically crafted RRDP XML files CVSS 4.0HIGH 8.7
TI-2026-36433 Routinator exits when accepting an incoming HTTP or RTR connection fails CVSS 4.0HIGH 8.7

See all 96 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences