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TI-2026-54211 Aliases CVE-2026-77860GHSA-8483-8qxh-jcf2

'serve-expired' can bypass Unbound 'wait-limit'

Priority LOW 17CWE-675Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
High
Impact type
—
Confidentiality · integrity · availability
None · None · Low
Fix status
Partial Red Hat: 1 fixed, 4 without a fix

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

Summary

In NLnetLabs Unbound 1.20.0 up to and including 1.26.0, a vulnerability on the 'serve-expired' code path can cause a double decrement on the 'wait-limit' counter per client IP essentially bypassing one of the counter measures that was introduced for DNSBomb (CVE-2024-33655). A malicious actor can exploit this by controlling an authoritative zone with short TTL, so cached entries expire quickly. Each 'slow' query, one the attacker's authoritative never answers, is followed by one query for an expired cached name, which is answered immediately via the 'serve-expired' path and decrements the counter twice. This second query was named 'pump'. By alternating slow queries and pumps, the attacker keeps the per-client counter at or below the configured 'wait-limit' indefinitely, and can hold an arbitrary number of pending queries from a single source IP, up to the global mesh quota (num-queries-per-thread); eventually bypassing one of the counter measures introduced for DNSBomb (CVE-2024-33655). This vulnerability is present on the 'serve-expired' code path.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV
EPSS 0.00301 22nd percentileScored 2026-11-07
Fix Partial Unbound (NLnet Labs): 1.26.1Red Hat: 1 advisoryRed Hat: 1 fixed, 4 without a fix

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
None
Automatable
No
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 LabsUnbound1.20.0 to before 1.26.11.26.1Patch availableCNA
  • Unbound VendorNLnet Labs Affected 1.20.0 to before 1.26.1 Fixed in 1.26.1 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:*1.20.0 to before 1.26.1VulnerableNLNETLABS
  • cpe:2.3:a:nlnetlabs:unbound:*:*:*:*:*:*:*:* Versions 1.20.0 to before 1.26.1 Vulnerable ·NLNETLABS

Remediation

  • Fix · CNA Unbound (NLnet Labs) Fixed in 1.26.1

Red Hat 1 advisory

  • 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 ·

    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: Low. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat Enterprise Linux 10AffectedNo fix yet: Fix deferred
Red Hat Enterprise Linux 9AffectedNo fix yet: Fix deferred
Red Hat OpenShift Container Platform 4AffectedNo fix yet: Fix deferred
Red Hat OpenShift Container Platform 5AffectedNo fix yet: Fix deferred
Red Hat Hardened ImagesFixed RHSA-2026:68590
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-2026-77860
  2. 2026-10-03 Alias added: GHSA-8483-8qxh-jcf2
  3. 2026-11-07 Affected versions changed · Red Hat

References

Patch 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

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