🛡️ CVE-2026-56444 on Alpine — unbound

⚪ Unknown ✅ No Known Exploit OSV
N/A
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

In NLnet Labs Unbound 1.20.0 up to and including 1.25.1, when Unbound is configured with 'serve-expired: yes' and 'serve-expired-client-timeout > discard-timeout > 0' (contrary to the suggested values), the discard-timeout branch during the serve expired logic drops an aged client reply without performing the correct accounting for the number of reply addresses for the query. Other identical branches outside of serve expired perform the correct decrement. Since the counter is never decremented in such scenario, it can reach the maximum limit and new clients for duplicate in-flight queries are silently dropped resulting in degradation of resolution service. A malicious actor can exploit the vulnerability by querying the resolver for a client-controlled slow-on-demand authoritative zone that can drive the counter past the threshold. Shipped defaults for 'serve-expired-client-timeout: 1800' and 'discard-timeout: 1900' make the branch unreachable.

Distribution advisory

This page covers CVE-2026-56444 as tracked by Alpine, for the package unbound. The fix is available in version 1.25.2-r0; earlier versions remain affected.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is high, an attacker needs no privileges on the target. No user interaction is required. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality none, integrity none, availability high.

Affected software

ALPINE-CVE-2026-56444 is recorded against 1 package.

  • unbound (from 1.20.0 up to 1.25.2-r0)

Timeline and source

Published on 22 July 2026 and last revised on 28 July 2026. No public exploit is currently recorded for this entry. Record sourced from OSV.

References

security.alpinelinux.org (Advisory)

Details

Severity Unknown
CVSS Score N/A
CVSS Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
CWE N/A
Public Exploit ✅ No
Source OSV
Published 2026-07-22
Updated 2026-08-11
Modified 2026-07-28
Fix URL N/A

Affected Packages

Software From version Fixed in
unbound 1.20.0 1.25.2-r0

Vulnerability Monitoring

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