Low [CVE-2026-42955] DNS cache integrity issue
This low-severity Red Hat Linux advisory covers CVE-2026-42955 affecting Red Hat Hardened Images, Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 8.
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Summary
In NLnet Labs Unbound 1.16.2 up to and including 1.25.1, a similar vulnerability as with CVE-2026-40622 in the 'ghost domain names' family of attacks was found in Unbound that could extend the ghost domain window by up to one cached TTL configured value for A/AAAA glue records.
Similar to other 'ghost domain names' attacks, an adversary needs to control a (ghost) zone and be able to query a vulnerable Unbound. A single client A/AAAA query can cause Unbound to overwrite the cached expired parent-side glue rrset and essentially extend the ghost domain window by up to one cached TTL configured value ('cache-max-ttl').
In configurations where 'harden-referral-path: yes' is used (non-default configuration), no client query is required since Unbound implicitly performs that query. This is a variant of CVE-2026-40622 which only addressed the NS query.
A "ghost domain names" flaw in Unbound allows a remote attacker controlling a domain to manipulate cached DNS records. By extending the lifetime of outdated DNS information, an attacker can cause clients to receive stale or misleading DNS responses.
This Low impact DNS cache integrity issue in Unbound allows an attacker to extend the window for serving outdated DNS information. The risk is elevated if the non-default `harden-referral-path: yes` configuration is enabled, as it removes the need for a client query.
- 1.16.2
- 1.25.1
Official advisory · high-confidence parse· fetched 1 day ago·verify at source
- unbound-main-1.25.2-0.1.hum1
- RHSA-2026:43588
Official advisory · high-confidence parse· fetched 1 day ago·verify at source
Mitigation checklist
- To mitigate this issue, ensure harden-referral-path is set to no (the default) to prevent Unbound from implicitly triggering the vulnerable cache overwrites. Additionally, restrict recursive DNS access strictly to trusted clients to prevent external attackers from manually triggering the flaw. Restart the Unbound service to apply these configuration changes.
Official advisory · high-confidence parse· fetched 1 day ago·verify at source
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