CVEvulnerability

CVE-2026-77860

3.7 LOW Published 2026-09-16 Modified 2026-09-23 Official page ↗
Status
Analyzed
Published
2026-09-16
Last modified
2026-09-23
Assigner
[email protected]
CVSS 3.1 ([email protected])
3.7 LOW — CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L
Weaknesses
CWE-675

Description

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.

Affected configurations

• nlnetlabs unbound (>= 1.20.0 < 1.26.1)

Related

Weakness · CWE (1)

  • CWE-675 Multiple Operations on Resource in Single-Operation Context weakness

References