CVE-2026-77860 Affecting unbound-devel package, versions <1.26.1-150100.10.31.1


Severity

Recommended
medium

Based on SUSE Linux Enterprise Server security rating.

Threat Intelligence

EPSS
0.3% (21st percentile)

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  • Snyk IDSNYK-SLES154-UNBOUNDDEVEL-20876238
  • published13 Oct 2026
  • disclosed12 Oct 2026

Introduced: 12 Oct 2026

NewCVE-2026-77860  (opens in a new tab)

How to fix?

Upgrade SLES:15.4 unbound-devel to version 1.26.1-150100.10.31.1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream unbound-devel package and not the unbound-devel package as distributed by SLES. See How to fix? for SLES:15.4 relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1