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VulnerabilityPublished

CVE-2026-77860: NLnet Labs Unbound · Multiple Operations on Resource in Single-Operation Context

Affects NLnet Labs UnboundSource CVE Database V5

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Mentioned vulnerabilities

Not known to be exploited · CVSS 3.7 Low : upgrade to 1.26.1 when convenient.

Data as of 31 Oct 2026, 08:20 UTC

CVSS 3.1 base score
3.7Low
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.3% chance of exploitation in 30 days – higher than 22% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 1.26.1
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 16 Sep 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 30 Oct 2026.

What to do

Upgrade NLnet Labs Unbound to 1.26.1.

Affected software

ProductAffectedFixed in
NLnet LabsUnboundAffected
  • >=1.20.0 <1.26.1
Fixed in
  • 1.26.1

AI-suggested

No explicit patch or fix is stated in the provided data. Since this vulnerability is related to a specific code path and countermeasure bypass, generic mitigations unrelated to this context are not recommended.

Description

NLnet Labs Unbound versions 1.20.0 through 1.26.0 contain a vulnerability in the 'serve-expired' code path that allows a double decrement of the 'wait-limit' counter per client IP. This flaw can be exploited by an attacker controlling an authoritative zone with short TTLs to bypass a DNS query rate-limiting countermeasure introduced for DNSBomb (CVE-2024-33655). The attacker can maintain the per-client counter at or below the configured limit indefinitely, allowing an arbitrary number of pending queries from a single source IP. The vulnerability has a CVSS score of 3.7 and is classified as medium severity.

References

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