TI-2026-56296 Aliases CVE-2026-81634 GHSA-x9ff-rj4v-x6mq

Possible heap buffer overflow during DNSSEC canonicalization

LOW 39CWE-122Published 2026-09-16 · Updated 2026-09-16

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Impact type: Denial of service
Confidentiality · integrity · availability: None · None · High
Fix status: Partial Red Hat: 7 fixed, 4 without a fix

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat. Impact type from CWE-122 and the CVSS impact.

Summary

In NLnet Labs Unbound up to and including 1.26.0, a 255 length query name with a large TCP response can lead to a heap buffer overflow during the RRSet canonicalisation routine. This is caused by missing to add the first owner name into the buffer length check. A malicious actor operating a malicious name server or tampering with an incoming response to Unbound (canonicalisation happens before DNSSEC validation), can trigger the vulnerability.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.0048 41st percentileScored 2026-11-07

Fix Partial Unbound (NLnet Labs): 1.26.1Red Hat: 5 advisoriesRed Hat: 7 fixed, 4 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 1.26.1	1.26.1	Patch available	CNA

Unbound VendorNLnet Labs Affected before 1.26.1 Fixed in 1.26.1 Patch available CNA

CPE configurations NVD · 1

CPE	Versions	Role	Vendor
cpe:2.3:a:nlnetlabs:unbound::::::::	before 1.26.1	Vulnerable	NLNETLABS

cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:* Versions before 1.26.1 Vulnerable ·NLNETLABS

Remediation

Fix · CNA Unbound (NLnet Labs) Fixed in 1.26.1

Red Hat 5 advisories

RHSA-2026:74428 Released 2026-10-06 · Red Hat rating Important
OpenShift Container Platform 4.22.17 bug fix and security update
- Red Hat OpenShift Container Platform 4.22 rhcos-aarch64-4.22.9.8.202609291947-0, rhcos-ppc64le-4.22.9.8.202609291947-0, rhcos-s390x-4.22.9.8.202609291947-0 +1
RHSA-2026:71487 Released 2026-09-24 · Red Hat rating Critical
unbound security update
- Red Hat Enterprise Linux AppStream (v. 9) python3-unbound-1.24.2-3.el9_8.8, unbound-1.24.2-3.el9_8.8, unbound-dracut-1.24.2-3.el9_8.8 +1
- Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) unbound-devel-1.24.2-3.el9_8.8
RHSA-2026:71419 Released 2026-09-24 · Red Hat rating Critical
unbound security update
- Red Hat Enterprise Linux AppStream (v. 10) python3-unbound-1.24.2-7.el10_2.6, unbound-1.24.2-7.el10_2.6, unbound-anchor-1.24.2-7.el10_2.6 +3
- Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) unbound-devel-1.24.2-7.el10_2.6

Show 2 more Red Hat advisories

RHSA-2026:70754 Released 2026-09-23 · Red Hat rating Critical
unbound security update
- Red Hat Enterprise Linux AppStream (v. 8) python3-unbound-1.16.2-5.14.el8_10.4, unbound-1.16.2-5.14.el8_10.4, unbound-devel-1.16.2-5.14.el8_10.4 +1
RHSA-2026:68590 Released 2026-09-17 · Red Hat rating Critical
Red Hat Hardened Images RPMs bug fix and enhancement update
- Red Hat Hardened Images python3-unbound-1.26.1-1.hum1@aarch64, python3-unbound-1.26.1-1.hum1@x86_64, unbound-1.26.1-1.hum1@aarch64 +14

Fixed in the same release

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

Release · 2026-09-16
NLnet Labs Unbound 1.26.1
9 records Highest priority Priority MEDIUM 2 MEDIUM, 7 LOW
Other records, highest priority first
- TI-2026-56302 Heap buffer overflow and possible Remote Code Execution when digesting DNSKEYPriority MEDIUM 49
- TI-2026-57038 CNAME synthesis could lead to heap corruptionPriority MEDIUM 40
- TI-2026-58665 Retrap: Novel Vulnerabilities to launch Algorithmic Complexity Attacks on DNSSECPriority LOW 39
Show all 9 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 planned: Out of support scope
Red Hat Enterprise Linux 7	Affected	No fix yet
Red Hat OpenShift Container Platform 4	Affected	No fix yet
Red Hat OpenShift Container Platform 5	Affected	No fix yet
Red Hat Enterprise Linux AppStream (v. 10)	Fixed	RHSA-2026:71419
Red Hat Enterprise Linux AppStream (v. 8)	Fixed	RHSA-2026:70754
Red Hat Enterprise Linux AppStream (v. 9)	Fixed	RHSA-2026:71487
Red Hat Enterprise Linux CodeReady Linux Builder (v. 10)	Fixed	RHSA-2026:71419
Red Hat Enterprise Linux CodeReady Linux Builder (v. 9)	Fixed	RHSA-2026:71487
Red Hat Hardened Images	Fixed	RHSA-2026:68590
Red Hat OpenShift Container Platform 4.22	Fixed	RHSA-2026:74428

Timeline

2026-10-02 Threatist record created from CVE-2026-81634
2026-10-03 Alias added: GHSA-x9ff-rj4v-x6mq
2026-10-07 Fix available: RHSA-2026:74428 · Red Hat
2026-10-07 Fix available: Red Hat OpenShift Container Platform 4.22 · Red Hat
2026-10-30 Affected versions changed · Red Hat

References

Patch 1

https://www.nlnetlabs.nl/downloads/unbound/CVE-2026-81634.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