# CVE-2026-109125: unbound: In NLnet Labs Unbound up to and including version 1.26.1, an observable cache-level side-channel can be exposed with... CVE-2026-109125 is fixed in 12 products on 1 platform, first by DEBIAN-CVE-2026-109125, released October 24, 2026. It is not reported as exploited. Patch Radar priority: Routine. - Web page: https://patchblox.com/security/cve/CVE-2026-109125 - Priority: Routine - CVSS: 5.3 (medium) - EPSS: 0.0017 - CISA KEV: not listed - Exploited (vendor report): no - Publicly disclosed: no - Published: Oct 21, 2026 ## Description In NLnet Labs Unbound up to and including version 1.26.1, an observable cache-level side-channel can be exposed with 'unwanted-reply-threshold > 0' configurations (not a default configuration). If a response-like UDP datagram reaches the upstream source port currently used by a recursive query, but its TXID does not match any pending query, Unbound counts the packet as an unwanted reply. When the accumulated count reaches the configured threshold, Unbound clears the worker's RRset cache and message cache. This cache clear action does not destroy the current upstream UDP pending query. Therefore, an external observer can distinguish whether a candidate port matches the current upstream source port by checking whether an existing cached item has been cleared. This is a cache side-channel vulnerability that can be used to probe the upstream source port. Although the attack is not feasible on default configurations and the suggested value (10 million) makes it an ureliable attack on a public resolver, in scenarios where the attacker can keep a concurrent query window alive, the attacker can first filter the source port and then perform birthday-style guessing against the TXID, making cache poisoning a feasible attack path. ## Where it's fixed | Platform | Product | Fixed in | Fix | Released | |---|---|---|---|---| | Linux | python3-unbound amzn 2023 | 1.17.1-1.amzn2023.0.17 | [ALAS2023-2026-3313](https://patchblox.com/security/data/fix/linux/alas2023-2026-3313.md) | Nov 7, 2026 | | Linux | python3-unbound-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.17 | [ALAS2023-2026-3313](https://patchblox.com/security/data/fix/linux/alas2023-2026-3313.md) | Nov 7, 2026 | | Linux | unbound Debian 13.5 (trixie) | 1.26.2-0+deb13u1 | [DEBIAN-CVE-2026-109125](https://patchblox.com/security/data/fix/linux/debian-cve-2026-109125.md) | Oct 24, 2026 | | Linux | unbound Debian 14 | 1.26.2-1 | [DEBIAN-CVE-2026-109125](https://patchblox.com/security/data/fix/linux/debian-cve-2026-109125.md) | Oct 24, 2026 | | Linux | unbound amzn 2023 | 1.17.1-1.amzn2023.0.17 | [ALAS2023-2026-3313](https://patchblox.com/security/data/fix/linux/alas2023-2026-3313.md) | Nov 7, 2026 | | Linux | unbound-anchor amzn 2023 | 1.17.1-1.amzn2023.0.17 | [ALAS2023-2026-3313](https://patchblox.com/security/data/fix/linux/alas2023-2026-3313.md) | Nov 7, 2026 | | Linux | unbound-anchor-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.17 | [ALAS2023-2026-3313](https://patchblox.com/security/data/fix/linux/alas2023-2026-3313.md) | Nov 7, 2026 | | Linux | unbound-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.17 | [ALAS2023-2026-3313](https://patchblox.com/security/data/fix/linux/alas2023-2026-3313.md) | Nov 7, 2026 | | Linux | unbound-debugsource amzn 2023 | 1.17.1-1.amzn2023.0.17 | [ALAS2023-2026-3313](https://patchblox.com/security/data/fix/linux/alas2023-2026-3313.md) | Nov 7, 2026 | | Linux | unbound-devel amzn 2023 | 1.17.1-1.amzn2023.0.17 | [ALAS2023-2026-3313](https://patchblox.com/security/data/fix/linux/alas2023-2026-3313.md) | Nov 7, 2026 | | Linux | unbound-libs amzn 2023 | 1.17.1-1.amzn2023.0.17 | [ALAS2023-2026-3313](https://patchblox.com/security/data/fix/linux/alas2023-2026-3313.md) | Nov 7, 2026 | | Linux | unbound-libs-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.17 | [ALAS2023-2026-3313](https://patchblox.com/security/data/fix/linux/alas2023-2026-3313.md) | Nov 7, 2026 | | Linux | unbound-utils amzn 2023 | 1.17.1-1.amzn2023.0.17 | [ALAS2023-2026-3313](https://patchblox.com/security/data/fix/linux/alas2023-2026-3313.md) | Nov 7, 2026 | | Linux | unbound-utils-debuginfo amzn 2023 | 1.17.1-1.amzn2023.0.17 | [ALAS2023-2026-3313](https://patchblox.com/security/data/fix/linux/alas2023-2026-3313.md) | Nov 7, 2026 | --- Data as of 2026-11-09T13:31:49Z UTC. 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