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TI-2026-40374 Aliases CVE-2026-55973GHSA-g479-fg97-pf5w

'dns-error-reporting: yes' leads to stack buffer overflow

Priority LOW 39CWE-20Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
None · None · High
Fix status
Partial Red Hat: 6 fixed, 1 without a fix

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat.

Summary

In NLnet Labs Unbound 1.23.0 up to and including 1.25.1, when 'dns-error-reporting: yes' is set, the EDNS Report-Channel option (code 18) from the last upstream response is read and uses the option's length as the length of the agent domain. When a domain name check is performed on the agent domain, the returned lenght is not used and if the agent domain is followed by garbage, those bytes are moved onto the tail of the synthetic '_er.' report query name. That query name is later used in the iterator via a subquery to send out the DNS Error Report and when Unbound tries to walk that query name during 'find_closest_of_type()', it strips labels using the query name length rather than stopping at the embedded root, walks one byte past it, and feeds the first garbage byte to 'dname_query_hash()' as a label length writing over the stack variable 'labuf'. One ordinary upstream response from a delegated zone the attacker controls is sufficient to terminate the daemon.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00281 20th percentileScored 2026-11-07
Fix Partial Unbound (NLnet Labs): 1.25.2Red Hat: 5 advisoriesRed Hat: 6 fixed, 1 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

VendorProductAffected versionsFixed inStatusSource
NLnet LabsUnbound1.23.0 to before 1.25.21.25.2Patch availableCNA
  • Unbound VendorNLnet Labs Affected 1.23.0 to before 1.25.2 Fixed in 1.25.2 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*1.23.0 to before 1.25.2VulnerableNLNETLABS
  • cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:* Versions 1.23.0 to before 1.25.2 Vulnerable ·NLNETLABS

Remediation

  • Fix · CNA Unbound (NLnet Labs) Fixed in 1.25.2

Red Hat 5 advisories

  • RHSA-2026:66357 Released 2026-09-15 · Red Hat rating Important
    OpenShift Container Platform 4.22.14 bug fix and security update
    • Red Hat OpenShift Container Platform 4.22 rhcos-aarch64-4.22.9.8.202609081748-0, rhcos-ppc64le-4.22.9.8.202609081748-0, rhcos-s390x-4.22.9.8.202609081748-0 +1
  • RHSA-2026:60440 Released 2026-09-01 · Red Hat rating Important
    OpenShift Container Platform 4.22.12 bug fix and security update
    • Red Hat OpenShift Container Platform 4.22 rhcos-aarch64-4.22.9.8.202608251819-0, rhcos-ppc64le-4.22.9.8.202608251819-0, rhcos-s390x-4.22.9.8.202608251819-0 +1
  • RHSA-2026:55892 Released 2026-08-17 · Red Hat rating Important
    unbound security update
    • Red Hat Enterprise Linux AppStream (v. 10) python3-unbound-1.24.2-7.el10_2.4, unbound-1.24.2-7.el10_2.4, unbound-anchor-1.24.2-7.el10_2.4 +3
    • Red Hat Enterprise Linux CodeReady Linux Builder (v. 10) unbound-devel-1.24.2-7.el10_2.4
Show 2 more Red Hat advisories
  • RHSA-2026:55841 Released 2026-08-17 · Red Hat rating Important
    unbound security update
    • Red Hat Enterprise Linux AppStream (v. 9) python3-unbound-1.24.2-3.el9_8.4, unbound-1.24.2-3.el9_8.4, unbound-dracut-1.24.2-3.el9_8.4 +1
    • Red Hat Enterprise Linux CodeReady Linux Builder (v. 9) unbound-devel-1.24.2-3.el9_8.4
  • RHSA-2026:43588 Released 2026-07-22 · Red Hat rating Important
    Red Hat Hardened Images RPMs bug fix and enhancement update
    • Red Hat Hardened Images python3-unbound-1.25.2-0.1.hum1@aarch64, python3-unbound-1.25.2-0.1.hum1@x86_64, unbound-1.25.2-0.1.hum1@aarch64 +14

Fixed in the same release

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

  • Release ·

    NLnet Labs Unbound 1.25.2

    24 records Highest priority Priority LOW 24 LOW

    Other records, highest priority first

    • TI-2026-29375 Packet of death for DNSCrypt over TCPPriority LOW 39
    • TI-2026-25166 Remote DNS-over-QUIC denial of service due to `quic-size` budget bypassPriority LOW 39
    • TI-2026-32581 Cross-zone wildcard cache poisoning via RRSIG.labels manipulationPriority LOW 38
    Show all 24 records →

Vendor assessments

Red Hat

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

ProductStatusPlan or fix
Red Hat OpenShift Container Platform 5AffectedNo fix yet
Red Hat Enterprise Linux AppStream (v. 10)Fixed RHSA-2026:55892
Red Hat Enterprise Linux AppStream (v. 9)Fixed RHSA-2026:55841
Red Hat Enterprise Linux CodeReady Linux Builder (v. 10)Fixed RHSA-2026:55892
Red Hat Enterprise Linux CodeReady Linux Builder (v. 9)Fixed RHSA-2026:55841
Red Hat Hardened ImagesFixed RHSA-2026:43588
Red Hat OpenShift Container Platform 4.22Fixed RHSA-2026:60440, RHSA-2026:66357
Not affected: 4 products
  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 7
  • Red Hat Enterprise Linux 8
  • Red Hat OpenShift Container Platform 4

Timeline

  1. 2026-10-02 Threatist record created from CVE-2026-55973
  2. 2026-10-03 Alias added: GHSA-g479-fg97-pf5w
  3. 2026-11-02 Affected versions changed · Red Hat

References

Advisory 1

  • 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

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